diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d0f9597..9634de3 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -55,6 +55,12 @@ is documented. At the minimum document all the exported symbols.
 Make sure you commit `go.mod` and `go.sum` changes. Make sure you
 run `go mod tidy` to minimize such changes.
 
+## Implementation requirements
+
+Please, use `./internal/atomicx` rather than `atomic/sync`.
+
+Do now use `os/exec`, use `x/sys/execabs`.
+
 ## Code testing requirements
 
 Make sure all tests pass with `go test -race ./...` run from the
diff --git a/cmd/ooniprobe/internal/autorun/autorun_darwin.go b/cmd/ooniprobe/internal/autorun/autorun_darwin.go
index 80225f3..4f2499b 100644
--- a/cmd/ooniprobe/internal/autorun/autorun_darwin.go
+++ b/cmd/ooniprobe/internal/autorun/autorun_darwin.go
@@ -13,7 +13,7 @@ import (
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/cmd/ooniprobe/internal/utils"
-	"github.com/ooni/probe-cli/v3/internal/engine/shellx"
+	"github.com/ooni/probe-cli/v3/internal/shellx"
 	"golang.org/x/sys/execabs"
 	"golang.org/x/sys/unix"
 )
diff --git a/cmd/ooniprobe/internal/nettests/dnscheck.go b/cmd/ooniprobe/internal/nettests/dnscheck.go
index 02cf963..5fba9a9 100644
--- a/cmd/ooniprobe/internal/nettests/dnscheck.go
+++ b/cmd/ooniprobe/internal/nettests/dnscheck.go
@@ -5,7 +5,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/dnscheck"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/run"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // DNSCheck nettest implementation.
diff --git a/cmd/ooniprobe/internal/ooni/ooni.go b/cmd/ooniprobe/internal/ooni/ooni.go
index 41fd682..34658dd 100644
--- a/cmd/ooniprobe/internal/ooni/ooni.go
+++ b/cmd/ooniprobe/internal/ooni/ooni.go
@@ -6,7 +6,6 @@ import (
 	"io/ioutil"
 	"os"
 	"os/signal"
-	"sync/atomic"
 	"syscall"
 
 	"github.com/apex/log"
@@ -14,8 +13,10 @@ import (
 	"github.com/ooni/probe-cli/v3/cmd/ooniprobe/internal/database"
 	"github.com/ooni/probe-cli/v3/cmd/ooniprobe/internal/enginex"
 	"github.com/ooni/probe-cli/v3/cmd/ooniprobe/internal/utils"
-	engine "github.com/ooni/probe-cli/v3/internal/engine"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/engine"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/assetsdir"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/pkg/errors"
 	"upper.io/db.v3/lib/sqlbuilder"
 )
@@ -53,11 +54,7 @@ type Probe struct {
 	dbPath     string
 	configPath string
 
-	// We need to use a int32 in order to use the atomic.AddInt32/LoadInt32
-	// operations to ensure consistent reads of the variables. We do not use
-	// a 64 bit integer here because that may lead to crashes with 32 bit
-	// OSes as documented in https://golang.org/pkg/sync/atomic/#pkg-note-BUG.
-	isTerminatedAtomicInt int32
+	isTerminated *atomicx.Int64
 
 	softwareName    string
 	softwareVersion string
@@ -96,13 +93,12 @@ func (p *Probe) TempDir() string {
 // IsTerminated checks to see if the isTerminatedAtomicInt is set to a non zero
 // value and therefore we have received the signal to shutdown the running test
 func (p *Probe) IsTerminated() bool {
-	i := atomic.LoadInt32(&p.isTerminatedAtomicInt)
-	return i != 0
+	return p.isTerminated.Load() != 0
 }
 
 // Terminate interrupts the running context
 func (p *Probe) Terminate() {
-	atomic.AddInt32(&p.isTerminatedAtomicInt, 1)
+	p.isTerminated.Add(1)
 }
 
 // ListenForSignals will listen for SIGINT and SIGTERM. When it receives those
@@ -203,7 +199,7 @@ func (p *Probe) Init(softwareName, softwareVersion string) error {
 // current configuration inside the context. The caller must close
 // the session when done using it, by calling sess.Close().
 func (p *Probe) NewSession(ctx context.Context) (*engine.Session, error) {
-	kvstore, err := engine.NewFileSystemKVStore(
+	kvstore, err := kvstore.NewFS(
 		utils.EngineDir(p.home),
 	)
 	if err != nil {
@@ -234,10 +230,10 @@ func (p *Probe) NewProbeEngine(ctx context.Context) (ProbeEngine, error) {
 // NewProbe creates a new probe instance.
 func NewProbe(configPath string, homePath string) *Probe {
 	return &Probe{
-		home:                  homePath,
-		config:                &config.Config{},
-		configPath:            configPath,
-		isTerminatedAtomicInt: 0,
+		home:         homePath,
+		config:       &config.Config{},
+		configPath:   configPath,
+		isTerminated: &atomicx.Int64{},
 	}
 }
 
diff --git a/internal/atomicx/atomicx.go b/internal/atomicx/atomicx.go
new file mode 100644
index 0000000..33ddf1a
--- /dev/null
+++ b/internal/atomicx/atomicx.go
@@ -0,0 +1,43 @@
+// Package atomicx extends sync/atomic.
+//
+// Sync/atomic fails when using int64 atomic operations on 32 bit platforms
+// when the access is not aligned. As specified in the documentation, in
+// fact, "it is the caller's responsibility to arrange for 64-bit alignment
+// of 64-bit words accessed atomically". For more information on this
+// issue, see https://golang.org/pkg/sync/atomic/#pkg-note-BUG.
+//
+// As explained in CONTRIBUTING.md, probe-cli SHOULD use this package rather
+// than sync/atomic to avoid these alignment issues on 32 bit.
+//
+// It is of course possible to write atomic code using 64 bit variables on a
+// 32 bit platform, but that's difficult to do correctly. This package
+// provides an easier-to-use interface. We use allocated
+// structures protected by a mutex that encapsulate a int64 value.
+//
+// While there we also added support for atomic float64 operations, again
+// by using structures protected by a mutex variable.
+package atomicx
+
+import "sync"
+
+// Int64 is an int64 with atomic semantics.
+type Int64 struct {
+	// mu provides mutual exclusion.
+	mu sync.Mutex
+
+	// v is the underlying value.
+	v int64
+}
+
+// Add behaves like atomic.AddInt64.
+func (i64 *Int64) Add(delta int64) int64 {
+	i64.mu.Lock()
+	defer i64.mu.Unlock()
+	i64.v += delta
+	return i64.v
+}
+
+// Load behaves like atomic.LoadInt64.
+func (i64 *Int64) Load() (v int64) {
+	return i64.Add(0)
+}
diff --git a/internal/atomicx/atomicx_test.go b/internal/atomicx/atomicx_test.go
new file mode 100644
index 0000000..fec8d87
--- /dev/null
+++ b/internal/atomicx/atomicx_test.go
@@ -0,0 +1,28 @@
+package atomicx_test
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+)
+
+func TestInt64(t *testing.T) {
+	v := &atomicx.Int64{}
+	var wg sync.WaitGroup
+	// many goroutines update the value in parallel
+	for i := 0; i < 31; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			v.Add(1)
+		}()
+	}
+	wg.Wait()
+	if v.Add(3) != 34 {
+		t.Fatal("unexpected result")
+	}
+	if v.Load() != 34 {
+		t.Fatal("unexpected result")
+	}
+}
diff --git a/internal/cmd/apitool/main.go b/internal/cmd/apitool/main.go
index 61e1e44..69a8eff 100644
--- a/internal/cmd/apitool/main.go
+++ b/internal/cmd/apitool/main.go
@@ -16,11 +16,11 @@ import (
 	"os"
 
 	"github.com/apex/log"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpx"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
 
@@ -34,9 +34,9 @@ func newclient() probeservices.Client {
 			Logger:     log.Log,
 			UserAgent:  ua,
 		},
-		LoginCalls:    atomicx.NewInt64(),
-		RegisterCalls: atomicx.NewInt64(),
-		StateFile:     probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore()),
+		LoginCalls:    &atomicx.Int64{},
+		RegisterCalls: &atomicx.Int64{},
+		StateFile:     probeservices.NewStateFile(&kvstore.Memory{}),
 	}
 }
 
diff --git a/internal/cmd/jafar/iptables/iptables.go b/internal/cmd/jafar/iptables/iptables.go
index 7743eea..580e8bf 100644
--- a/internal/cmd/jafar/iptables/iptables.go
+++ b/internal/cmd/jafar/iptables/iptables.go
@@ -4,7 +4,7 @@
 package iptables
 
 import (
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 type shell interface {
diff --git a/internal/cmd/jafar/iptables/iptables_integration_test.go b/internal/cmd/jafar/iptables/iptables_integration_test.go
index 2d10337..659fec2 100644
--- a/internal/cmd/jafar/iptables/iptables_integration_test.go
+++ b/internal/cmd/jafar/iptables/iptables_integration_test.go
@@ -17,7 +17,7 @@ import (
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/resolver"
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/uncensored"
-	"github.com/ooni/probe-cli/v3/internal/engine/shellx"
+	"github.com/ooni/probe-cli/v3/internal/shellx"
 )
 
 func init() {
diff --git a/internal/cmd/jafar/iptables/iptables_linux.go b/internal/cmd/jafar/iptables/iptables_linux.go
index 058c9b6..1664a66 100644
--- a/internal/cmd/jafar/iptables/iptables_linux.go
+++ b/internal/cmd/jafar/iptables/iptables_linux.go
@@ -3,8 +3,8 @@
 package iptables
 
 import (
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
-	"github.com/ooni/probe-cli/v3/internal/engine/shellx"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/shellx"
 )
 
 type linuxShell struct{}
diff --git a/internal/cmd/jafar/main.go b/internal/cmd/jafar/main.go
index eb4bb41..f7b1941 100644
--- a/internal/cmd/jafar/main.go
+++ b/internal/cmd/jafar/main.go
@@ -26,8 +26,8 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/resolver"
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/tlsproxy"
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/uncensored"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
-	"github.com/ooni/probe-cli/v3/internal/engine/shellx"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/shellx"
 )
 
 var (
diff --git a/internal/cmd/jafar/main_test.go b/internal/cmd/jafar/main_test.go
index 5c356f1..6d4ac62 100644
--- a/internal/cmd/jafar/main_test.go
+++ b/internal/cmd/jafar/main_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/cmd/jafar/iptables"
-	"github.com/ooni/probe-cli/v3/internal/engine/shellx"
+	"github.com/ooni/probe-cli/v3/internal/shellx"
 )
 
 func ensureWeStartOverWithIPTables() {
diff --git a/internal/cmd/jafar/uncensored/uncensored.go b/internal/cmd/jafar/uncensored/uncensored.go
index 9fce757..ab43125 100644
--- a/internal/cmd/jafar/uncensored/uncensored.go
+++ b/internal/cmd/jafar/uncensored/uncensored.go
@@ -10,7 +10,7 @@ import (
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // Client is DNS, HTTP, and TCP client.
diff --git a/internal/cmd/miniooni/libminiooni.go b/internal/cmd/miniooni/libminiooni.go
index d023e40..9106883 100644
--- a/internal/cmd/miniooni/libminiooni.go
+++ b/internal/cmd/miniooni/libminiooni.go
@@ -17,10 +17,11 @@ import (
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/engine"
-	"github.com/ooni/probe-cli/v3/internal/engine/humanizex"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/assetsdir"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/selfcensor"
+	"github.com/ooni/probe-cli/v3/internal/humanize"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/version"
 	"github.com/pborman/getopt/v2"
 )
@@ -348,7 +349,7 @@ func MainWithConfiguration(experimentName string, currentOptions Options) {
 	}
 
 	kvstore2dir := filepath.Join(miniooniDir, "kvstore2")
-	kvstore, err := engine.NewFileSystemKVStore(kvstore2dir)
+	kvstore, err := kvstore.NewFS(kvstore2dir)
 	fatalOnError(err, "cannot create kvstore2 directory")
 
 	tunnelDir := filepath.Join(miniooniDir, "tunnel")
@@ -377,8 +378,8 @@ func MainWithConfiguration(experimentName string, currentOptions Options) {
 	defer func() {
 		sess.Close()
 		log.Infof("whole session: recv %s, sent %s",
-			humanizex.SI(sess.KibiBytesReceived()*1024, "byte"),
-			humanizex.SI(sess.KibiBytesSent()*1024, "byte"),
+			humanize.SI(sess.KibiBytesReceived()*1024, "byte"),
+			humanize.SI(sess.KibiBytesSent()*1024, "byte"),
 		)
 	}()
 	log.Debugf("miniooni temporary directory: %s", sess.TempDir())
@@ -426,8 +427,8 @@ func MainWithConfiguration(experimentName string, currentOptions Options) {
 	experiment := builder.NewExperiment()
 	defer func() {
 		log.Infof("experiment: recv %s, sent %s",
-			humanizex.SI(experiment.KibiBytesReceived()*1024, "byte"),
-			humanizex.SI(experiment.KibiBytesSent()*1024, "byte"),
+			humanize.SI(experiment.KibiBytesReceived()*1024, "byte"),
+			humanize.SI(experiment.KibiBytesSent()*1024, "byte"),
 		)
 	}()
 
diff --git a/internal/cmd/oohelper/internal/client.go b/internal/cmd/oohelper/internal/client.go
index 60e98ac..74d665f 100644
--- a/internal/cmd/oohelper/internal/client.go
+++ b/internal/cmd/oohelper/internal/client.go
@@ -15,7 +15,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpheader"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
 
diff --git a/internal/cmd/oohelper/internal/fake_test.go b/internal/cmd/oohelper/internal/fake_test.go
index dd09aaa..13bcdb9 100644
--- a/internal/cmd/oohelper/internal/fake_test.go
+++ b/internal/cmd/oohelper/internal/fake_test.go
@@ -8,7 +8,7 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 )
 
@@ -19,11 +19,11 @@ type FakeResolver struct {
 }
 
 func NewFakeResolverThatFails() FakeResolver {
-	return FakeResolver{NumFailures: atomicx.NewInt64(), Err: ErrNotFound}
+	return FakeResolver{NumFailures: &atomicx.Int64{}, Err: ErrNotFound}
 }
 
 func NewFakeResolverWithResult(r []string) FakeResolver {
-	return FakeResolver{NumFailures: atomicx.NewInt64(), Result: r}
+	return FakeResolver{NumFailures: &atomicx.Int64{}, Result: r}
 }
 
 var ErrNotFound = &net.DNSError{
diff --git a/internal/cmd/oohelper/oohelper.go b/internal/cmd/oohelper/oohelper.go
index 914ea8e..46977bc 100644
--- a/internal/cmd/oohelper/oohelper.go
+++ b/internal/cmd/oohelper/oohelper.go
@@ -12,7 +12,7 @@ import (
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/cmd/oohelper/internal"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 var (
diff --git a/internal/cmd/oohelperd/internal/fake_test.go b/internal/cmd/oohelperd/internal/fake_test.go
index 4eb77aa..95abe2c 100644
--- a/internal/cmd/oohelperd/internal/fake_test.go
+++ b/internal/cmd/oohelperd/internal/fake_test.go
@@ -8,7 +8,7 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 )
 
@@ -19,11 +19,11 @@ type FakeResolver struct {
 }
 
 func NewFakeResolverThatFails() FakeResolver {
-	return FakeResolver{NumFailures: atomicx.NewInt64(), Err: ErrNotFound}
+	return FakeResolver{NumFailures: &atomicx.Int64{}, Err: ErrNotFound}
 }
 
 func NewFakeResolverWithResult(r []string) FakeResolver {
-	return FakeResolver{NumFailures: atomicx.NewInt64(), Result: r}
+	return FakeResolver{NumFailures: &atomicx.Int64{}, Result: r}
 }
 
 var ErrNotFound = &net.DNSError{
diff --git a/internal/engine/atomicx/README.md b/internal/engine/atomicx/README.md
deleted file mode 100644
index 8a8fb95..0000000
--- a/internal/engine/atomicx/README.md
+++ /dev/null
@@ -1,3 +0,0 @@
-# Package github.com/ooni/probe-engine/atomicx
-
-Atomic int64/float64 that works also on 32 bit platforms.
diff --git a/internal/engine/atomicx/atomicx.go b/internal/engine/atomicx/atomicx.go
deleted file mode 100644
index 3c02d88..0000000
--- a/internal/engine/atomicx/atomicx.go
+++ /dev/null
@@ -1,68 +0,0 @@
-// Package atomicx contains atomic int64/float64 that work also on 32 bit
-// platforms. The main reason for rolling out this package is to avoid potential
-// crashes when using 32 bit devices where we are atomically accessing a 64 bit
-// variable that is not aligned. The solution to this issue is rather crude: use
-// a normal variable and protect it using a normal mutex. While this could be
-// disappointing in general, it seems fine to be done in our context where
-// we mainly use atomic semantics for counting.
-package atomicx
-
-import (
-	"sync"
-)
-
-// Int64 is an int64 with atomic semantics.
-type Int64 struct {
-	mu sync.Mutex
-	v  int64
-}
-
-// NewInt64 creates a new int64 with atomic semantics.
-func NewInt64() *Int64 {
-	return new(Int64)
-}
-
-// Add behaves like atomic.AddInt64
-func (i64 *Int64) Add(delta int64) (newvalue int64) {
-	i64.mu.Lock()
-	i64.v += delta
-	newvalue = i64.v
-	i64.mu.Unlock()
-	return
-}
-
-// Load behaves like atomic.LoadInt64
-func (i64 *Int64) Load() (v int64) {
-	i64.mu.Lock()
-	v = i64.v
-	i64.mu.Unlock()
-	return
-}
-
-// Float64 is an float64 with atomic semantics.
-type Float64 struct {
-	mu sync.Mutex
-	v  float64
-}
-
-// NewFloat64 creates a new float64 with atomic semantics.
-func NewFloat64() *Float64 {
-	return new(Float64)
-}
-
-// Add behaves like AtomicInt64.Add but for float64
-func (f64 *Float64) Add(delta float64) (newvalue float64) {
-	f64.mu.Lock()
-	f64.v += delta
-	newvalue = f64.v
-	f64.mu.Unlock()
-	return
-}
-
-// Load behaves like LoadInt64.Load buf for float64
-func (f64 *Float64) Load() (v float64) {
-	f64.mu.Lock()
-	v = f64.v
-	f64.mu.Unlock()
-	return
-}
diff --git a/internal/engine/atomicx/atomicx_test.go b/internal/engine/atomicx/atomicx_test.go
deleted file mode 100644
index baab7ff..0000000
--- a/internal/engine/atomicx/atomicx_test.go
+++ /dev/null
@@ -1,50 +0,0 @@
-package atomicx_test
-
-import (
-	"testing"
-	"time"
-
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
-)
-
-func TestInt64(t *testing.T) {
-	// TODO(bassosimone): how to write tests with race conditions
-	// and be confident that they're WAI? Here I hope this test is
-	// run with `-race` and I'm doing something that AFAICT will
-	// be flagged as race if we were not be using mutexes.
-	v := atomicx.NewInt64()
-	go func() {
-		v.Add(17)
-	}()
-	go func() {
-		v.Add(14)
-	}()
-	time.Sleep(1 * time.Second)
-	if v.Add(3) != 34 {
-		t.Fatal("unexpected result")
-	}
-	if v.Load() != 34 {
-		t.Fatal("unexpected result")
-	}
-}
-
-func TestFloat64(t *testing.T) {
-	// TODO(bassosimone): how to write tests with race conditions
-	// and be confident that they're WAI? Here I hope this test is
-	// run with `-race` and I'm doing something that AFAICT will
-	// be flagged as race if we were not be using mutexes.
-	v := atomicx.NewFloat64()
-	go func() {
-		v.Add(17.0)
-	}()
-	go func() {
-		v.Add(14.0)
-	}()
-	time.Sleep(1 * time.Second)
-	if r := v.Add(3); r < 33.9 && r > 34.1 {
-		t.Fatal("unexpected result")
-	}
-	if v.Load() < 33.9 && v.Load() > 34.1 {
-		t.Fatal("unexpected result")
-	}
-}
diff --git a/internal/engine/experiment.go b/internal/engine/experiment.go
index cd6ad89..4035af1 100644
--- a/internal/engine/experiment.go
+++ b/internal/engine/experiment.go
@@ -10,7 +10,6 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/geolocate"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/platform"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/bytecounter"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/dialer"
@@ -168,7 +167,7 @@ func (e *Experiment) newMeasurement(input string) *model.Measurement {
 	}
 	m.AddAnnotation("engine_name", "ooniprobe-engine")
 	m.AddAnnotation("engine_version", version.Version)
-	m.AddAnnotation("platform", platform.Name())
+	m.AddAnnotation("platform", e.session.Platform())
 	return m
 }
 
diff --git a/internal/engine/experiment/dash/dash.go b/internal/engine/experiment/dash/dash.go
index 5fdfd14..5b285bd 100644
--- a/internal/engine/experiment/dash/dash.go
+++ b/internal/engine/experiment/dash/dash.go
@@ -15,11 +15,11 @@ import (
 	"time"
 
 	"github.com/montanaflynn/stats"
-	"github.com/ooni/probe-cli/v3/internal/engine/humanizex"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
+	"github.com/ooni/probe-cli/v3/internal/humanize"
 )
 
 const (
@@ -181,7 +181,7 @@ func (r runner) measure(
 		total += current.Received
 		avgspeed := 8 * float64(total) / time.Now().Sub(begin).Seconds()
 		percentage := float64(current.Iteration) / float64(numIterations)
-		message := fmt.Sprintf("streaming: speed: %s", humanizex.SI(avgspeed, "bit/s"))
+		message := fmt.Sprintf("streaming: speed: %s", humanize.SI(avgspeed, "bit/s"))
 		r.callbacks.OnProgress(percentage, message)
 		current.Iteration++
 		speed := float64(current.Received) / float64(current.Elapsed)
diff --git a/internal/engine/experiment/dnscheck/dnscheck.go b/internal/engine/experiment/dnscheck/dnscheck.go
index 6e8906c..197ce09 100644
--- a/internal/engine/experiment/dnscheck/dnscheck.go
+++ b/internal/engine/experiment/dnscheck/dnscheck.go
@@ -11,15 +11,15 @@ import (
 	"net/url"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 const (
@@ -31,7 +31,7 @@ const (
 // Endpoints keeps track of repeatedly measured endpoints.
 type Endpoints struct {
 	WaitTime  time.Duration
-	count     uint32
+	count     *atomicx.Int64
 	nextVisit map[string]time.Time
 	mu        sync.Mutex
 }
@@ -48,7 +48,10 @@ func (e *Endpoints) maybeSleep(resolverURL string, logger model.Logger) {
 		return
 	}
 	sleepTime := nextTime.Sub(now)
-	atomic.AddUint32(&e.count, 1)
+	if e.count == nil {
+		e.count = &atomicx.Int64{}
+	}
+	e.count.Add(1)
 	logger.Infof("waiting %v before testing %s again", sleepTime, resolverURL)
 	time.Sleep(sleepTime)
 }
diff --git a/internal/engine/experiment/dnscheck/dnscheck_test.go b/internal/engine/experiment/dnscheck/dnscheck_test.go
index 09de9d5..daec92d 100644
--- a/internal/engine/experiment/dnscheck/dnscheck_test.go
+++ b/internal/engine/experiment/dnscheck/dnscheck_test.go
@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"net/url"
-	"sync/atomic"
 	"testing"
 	"time"
 
@@ -221,7 +220,7 @@ func TestDNSCheckWait(t *testing.T) {
 	}
 	run("dot://one.one.one.one")
 	run("dot://1dot1dot1dot1.cloudflare-dns.com")
-	if atomic.LoadUint32(&endpoints.count) < 1 {
+	if endpoints.count.Load() < 1 {
 		t.Fatal("did not sleep")
 	}
 }
diff --git a/internal/engine/experiment/hhfm/hhfm.go b/internal/engine/experiment/hhfm/hhfm.go
index dce7924..2015a9f 100644
--- a/internal/engine/experiment/hhfm/hhfm.go
+++ b/internal/engine/experiment/hhfm/hhfm.go
@@ -17,7 +17,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpheader"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/randx"
+	"github.com/ooni/probe-cli/v3/internal/randx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
diff --git a/internal/engine/experiment/hirl/hirl.go b/internal/engine/experiment/hirl/hirl.go
index 6fa3f5c..8ec1134 100644
--- a/internal/engine/experiment/hirl/hirl.go
+++ b/internal/engine/experiment/hirl/hirl.go
@@ -11,7 +11,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/randx"
+	"github.com/ooni/probe-cli/v3/internal/randx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
diff --git a/internal/engine/experiment/ndt7/ndt7.go b/internal/engine/experiment/ndt7/ndt7.go
index 5fe3982..0c39336 100644
--- a/internal/engine/experiment/ndt7/ndt7.go
+++ b/internal/engine/experiment/ndt7/ndt7.go
@@ -11,10 +11,10 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/humanizex"
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/mlablocatev2"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/humanize"
 )
 
 const (
@@ -127,7 +127,7 @@ func (m *Measurer) doDownload(
 			// 50% of the whole experiment, hence the `/2.0`.
 			percentage := elapsed / paramMaxRuntimeUpperBound / 2.0
 			speed := float64(count) * 8.0 / elapsed
-			message := fmt.Sprintf(" download: speed %s", humanizex.SI(
+			message := fmt.Sprintf(" download: speed %s", humanize.SI(
 				float64(speed), "bit/s"))
 			tk.Summary.Download = speed / 1e03 /* bit/s => kbit/s */
 			callbacks.OnProgress(percentage, message)
@@ -197,7 +197,7 @@ func (m *Measurer) doUpload(
 			// the whole experiment, hence `0.5 +` and `/2.0`.
 			percentage := 0.5 + elapsed/paramMaxRuntimeUpperBound/2.0
 			speed := float64(count) * 8.0 / elapsed
-			message := fmt.Sprintf("   upload: speed %s", humanizex.SI(
+			message := fmt.Sprintf("   upload: speed %s", humanize.SI(
 				float64(speed), "bit/s"))
 			tk.Summary.Upload = speed / 1e03 /* bit/s => kbit/s */
 			callbacks.OnProgress(percentage, message)
diff --git a/internal/engine/experiment/psiphon/psiphon_test.go b/internal/engine/experiment/psiphon/psiphon_test.go
index d136db6..c33e8ef 100644
--- a/internal/engine/experiment/psiphon/psiphon_test.go
+++ b/internal/engine/experiment/psiphon/psiphon_test.go
@@ -8,7 +8,7 @@ import (
 	"time"
 
 	"github.com/apex/log"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/psiphon"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/mockable"
@@ -83,7 +83,7 @@ func TestRunWillPrintSomethingWithCancelledContext(t *testing.T) {
 		time.Sleep(2 * time.Second)
 		cancel() // fail after we've given the printer a chance to run
 	}
-	observer := observerCallbacks{progress: atomicx.NewInt64()}
+	observer := observerCallbacks{progress: &atomicx.Int64{}}
 	err := measurer.Run(ctx, newfakesession(), measurement, observer)
 	if !errors.Is(err, context.Canceled) {
 		t.Fatal("expected another error here")
diff --git a/internal/engine/experiment/telegram/telegram_test.go b/internal/engine/experiment/telegram/telegram_test.go
index f1afcc3..3a83813 100644
--- a/internal/engine/experiment/telegram/telegram_test.go
+++ b/internal/engine/experiment/telegram/telegram_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"
 
 	"github.com/apex/log"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/telegram"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/mockable"
@@ -271,9 +271,9 @@ func TestUpdateWebWithMixedResults(t *testing.T) {
 }
 
 func TestWeConfigureWebChecksToFailOnHTTPError(t *testing.T) {
-	called := atomicx.NewInt64()
-	failOnErrorHTTPS := atomicx.NewInt64()
-	failOnErrorHTTP := atomicx.NewInt64()
+	called := &atomicx.Int64{}
+	failOnErrorHTTPS := &atomicx.Int64{}
+	failOnErrorHTTP := &atomicx.Int64{}
 	measurer := telegram.Measurer{
 		Config: telegram.Config{},
 		Getter: func(ctx context.Context, g urlgetter.Getter) (urlgetter.TestKeys, error) {
diff --git a/internal/engine/experiment/tlstool/internal/splitter_test.go b/internal/engine/experiment/tlstool/internal/splitter_test.go
index f564880..aa318a9 100644
--- a/internal/engine/experiment/tlstool/internal/splitter_test.go
+++ b/internal/engine/experiment/tlstool/internal/splitter_test.go
@@ -4,7 +4,7 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/tlstool/internal"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/randx"
+	"github.com/ooni/probe-cli/v3/internal/randx"
 )
 
 func TestSplitter84restSmall(t *testing.T) {
diff --git a/internal/engine/experiment/tlstool/tlstool.go b/internal/engine/experiment/tlstool/tlstool.go
index cf965f2..3eee7e1 100644
--- a/internal/engine/experiment/tlstool/tlstool.go
+++ b/internal/engine/experiment/tlstool/tlstool.go
@@ -19,7 +19,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 const (
diff --git a/internal/engine/experiment/tor/tor.go b/internal/engine/experiment/tor/tor.go
index 09bc51f..cbe9f32 100644
--- a/internal/engine/experiment/tor/tor.go
+++ b/internal/engine/experiment/tor/tor.go
@@ -12,14 +12,14 @@ import (
 	"sync"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpheader"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netxlogger"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/oonidatamodel"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/oonitemplates"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 const (
@@ -264,7 +264,7 @@ func newResultsCollector(
 ) *resultsCollector {
 	rc := &resultsCollector{
 		callbacks:     callbacks,
-		completed:     atomicx.NewInt64(),
+		completed:     &atomicx.Int64{},
 		measurement:   measurement,
 		sess:          sess,
 		targetresults: make(map[string]TargetResults),
diff --git a/internal/engine/experiment/urlgetter/runner.go b/internal/engine/experiment/urlgetter/runner.go
index f02600d..3d7522d 100644
--- a/internal/engine/experiment/urlgetter/runner.go
+++ b/internal/engine/experiment/urlgetter/runner.go
@@ -13,7 +13,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/httpheader"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 const httpRequestFailed = "http_request_failed"
diff --git a/internal/engine/experiment/urlgetter/runner_test.go b/internal/engine/experiment/urlgetter/runner_test.go
index fa02c4e..9f9947b 100644
--- a/internal/engine/experiment/urlgetter/runner_test.go
+++ b/internal/engine/experiment/urlgetter/runner_test.go
@@ -9,7 +9,7 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpheader"
 )
@@ -235,7 +235,7 @@ func TestRunnerHTTPCannotReadBodyWinsOver400(t *testing.T) {
 
 func TestRunnerWeCanForceUserAgent(t *testing.T) {
 	expected := "antani/1.23.4-dev"
-	found := atomicx.NewInt64()
+	found := &atomicx.Int64{}
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Header.Get("User-Agent") == expected {
 			found.Add(1)
@@ -262,7 +262,7 @@ func TestRunnerWeCanForceUserAgent(t *testing.T) {
 
 func TestRunnerDefaultUserAgent(t *testing.T) {
 	expected := httpheader.UserAgent()
-	found := atomicx.NewInt64()
+	found := &atomicx.Int64{}
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Header.Get("User-Agent") == expected {
 			found.Add(1)
diff --git a/internal/engine/experiment/webconnectivity/endpoints.go b/internal/engine/experiment/webconnectivity/endpoints.go
index a228798..ac7d072 100644
--- a/internal/engine/experiment/webconnectivity/endpoints.go
+++ b/internal/engine/experiment/webconnectivity/endpoints.go
@@ -4,7 +4,7 @@ import (
 	"net"
 	"net/url"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // EndpointInfo describes a TCP/TLS endpoint.
diff --git a/internal/engine/experiment/webconnectivity/endpoints_test.go b/internal/engine/experiment/webconnectivity/endpoints_test.go
index 9baffbf..2fe7da8 100644
--- a/internal/engine/experiment/webconnectivity/endpoints_test.go
+++ b/internal/engine/experiment/webconnectivity/endpoints_test.go
@@ -6,12 +6,12 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
 )
 
 func TestNewEndpointPortPanicsWithInvalidScheme(t *testing.T) {
-	counter := atomicx.NewInt64()
+	counter := &atomicx.Int64{}
 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
@@ -30,7 +30,7 @@ func TestNewEndpointPortPanicsWithInvalidScheme(t *testing.T) {
 }
 
 func TestNewEndpointPortPanicsWithInvalidHost(t *testing.T) {
-	counter := atomicx.NewInt64()
+	counter := &atomicx.Int64{}
 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
diff --git a/internal/engine/experiment/webconnectivity/httpanalysis_test.go b/internal/engine/experiment/webconnectivity/httpanalysis_test.go
index fc69b1b..4c0c0f0 100644
--- a/internal/engine/experiment/webconnectivity/httpanalysis_test.go
+++ b/internal/engine/experiment/webconnectivity/httpanalysis_test.go
@@ -6,7 +6,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/randx"
+	"github.com/ooni/probe-cli/v3/internal/randx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
 )
 
diff --git a/internal/engine/experiment/whatsapp/whatsapp.go b/internal/engine/experiment/whatsapp/whatsapp.go
index eac221d..cb560a9 100644
--- a/internal/engine/experiment/whatsapp/whatsapp.go
+++ b/internal/engine/experiment/whatsapp/whatsapp.go
@@ -15,7 +15,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/httpfailure"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 const (
diff --git a/internal/engine/experiment/whatsapp/whatsapp_test.go b/internal/engine/experiment/whatsapp/whatsapp_test.go
index 89f13eb..abbc544 100644
--- a/internal/engine/experiment/whatsapp/whatsapp_test.go
+++ b/internal/engine/experiment/whatsapp/whatsapp_test.go
@@ -9,7 +9,7 @@ import (
 
 	"github.com/apex/log"
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/whatsapp"
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/httpfailure"
@@ -555,7 +555,7 @@ func TestTestKeysOnlyWebHTTPFailureTooManyURLs(t *testing.T) {
 }
 
 func TestWeConfigureWebChecksCorrectly(t *testing.T) {
-	called := atomicx.NewInt64()
+	called := &atomicx.Int64{}
 	emptyConfig := urlgetter.Config{}
 	configWithFailOnHTTPError := urlgetter.Config{FailOnHTTPError: true}
 	configWithNoFollowRedirects := urlgetter.Config{NoFollowRedirects: true}
diff --git a/internal/engine/geolocate/geolocate.go b/internal/engine/geolocate/geolocate.go
index 443eaed..d951e58 100644
--- a/internal/engine/geolocate/geolocate.go
+++ b/internal/engine/geolocate/geolocate.go
@@ -7,7 +7,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
 
diff --git a/internal/engine/geolocate/iplookup.go b/internal/engine/geolocate/iplookup.go
index 01462bd..994055a 100644
--- a/internal/engine/geolocate/iplookup.go
+++ b/internal/engine/geolocate/iplookup.go
@@ -9,7 +9,7 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/multierror"
+	"github.com/ooni/probe-cli/v3/internal/multierror"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 )
 
diff --git a/internal/engine/humanizex/humanizex_test.go b/internal/engine/humanizex/humanizex_test.go
deleted file mode 100644
index 75d0c2d..0000000
--- a/internal/engine/humanizex/humanizex_test.go
+++ /dev/null
@@ -1,34 +0,0 @@
-package humanizex_test
-
-import (
-	"testing"
-
-	"github.com/ooni/probe-cli/v3/internal/engine/humanizex"
-)
-
-func TestGood(t *testing.T) {
-	if humanizex.SI(128, "bit/s") != "128  bit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(1280, "bit/s") != "  1 kbit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(12800, "bit/s") != " 13 kbit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(128000, "bit/s") != "128 kbit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(1280000, "bit/s") != "  1 Mbit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(12800000, "bit/s") != " 13 Mbit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(128000000, "bit/s") != "128 Mbit/s" {
-		t.Fatal("unexpected result")
-	}
-	if humanizex.SI(1280000000, "bit/s") != "  1 Gbit/s" {
-		t.Fatal("unexpected result")
-	}
-}
diff --git a/internal/engine/inputloader.go b/internal/engine/inputloader.go
index d3d3d6e..3e4640d 100644
--- a/internal/engine/inputloader.go
+++ b/internal/engine/inputloader.go
@@ -8,8 +8,8 @@ import (
 	"io/fs"
 
 	"github.com/apex/log"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/fsx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/fsx"
 )
 
 // These errors are returned by the InputLoader.
@@ -154,7 +154,7 @@ func (il *InputLoader) loadLocal() ([]model.URLInfo, error) {
 		inputs = append(inputs, model.URLInfo{URL: input})
 	}
 	for _, filepath := range il.SourceFiles {
-		extra, err := il.readfile(filepath, fsx.Open)
+		extra, err := il.readfile(filepath, fsx.OpenFile)
 		if err != nil {
 			return nil, err
 		}
diff --git a/internal/engine/inputloader_network_test.go b/internal/engine/inputloader_network_test.go
index 729a869..5fba6e4 100644
--- a/internal/engine/inputloader_network_test.go
+++ b/internal/engine/inputloader_network_test.go
@@ -6,8 +6,8 @@ import (
 
 	"github.com/apex/log"
 	engine "github.com/ooni/probe-cli/v3/internal/engine"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 func TestInputLoaderInputOrQueryBackendWithNoInput(t *testing.T) {
@@ -19,7 +19,7 @@ func TestInputLoaderInputOrQueryBackendWithNoInput(t *testing.T) {
 			Address: "https://ams-pg-test.ooni.org/",
 			Type:    "https",
 		}},
-		KVStore:         kvstore.NewMemoryKeyValueStore(),
+		KVStore:         &kvstore.Memory{},
 		Logger:          log.Log,
 		SoftwareName:    "miniooni",
 		SoftwareVersion: "0.1.0-dev",
diff --git a/internal/engine/inputloader_test.go b/internal/engine/inputloader_test.go
index 9b2ee35..fb3e940 100644
--- a/internal/engine/inputloader_test.go
+++ b/internal/engine/inputloader_test.go
@@ -11,8 +11,8 @@ import (
 
 	"github.com/apex/log"
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 func TestInputLoaderInputNoneWithStaticInputs(t *testing.T) {
@@ -237,7 +237,7 @@ func TestInputLoaderInputOrQueryBackendWithInput(t *testing.T) {
 
 func TestInputLoaderInputOrQueryBackendWithNoInputAndCancelledContext(t *testing.T) {
 	sess, err := NewSession(context.Background(), SessionConfig{
-		KVStore:         kvstore.NewMemoryKeyValueStore(),
+		KVStore:         &kvstore.Memory{},
 		Logger:          log.Log,
 		SoftwareName:    "miniooni",
 		SoftwareVersion: "0.1.0-dev",
diff --git a/internal/engine/inputprocessor.go b/internal/engine/inputprocessor.go
index 2e890c1..c828cac 100644
--- a/internal/engine/inputprocessor.go
+++ b/internal/engine/inputprocessor.go
@@ -2,7 +2,6 @@ package engine
 
 import (
 	"context"
-	"sync/atomic"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
@@ -68,11 +67,6 @@ type InputProcessor struct {
 	// Submitter is the code that will submit measurements
 	// to the OONI collector.
 	Submitter InputProcessorSubmitterWrapper
-
-	// terminatedByMaxRuntime is an internal atomic variabile
-	// incremented when we're terminated by MaxRuntime. We
-	// only use this variable when testing.
-	terminatedByMaxRuntime int32
 }
 
 // InputProcessorSaverWrapper is InputProcessor's
@@ -129,29 +123,41 @@ func (ipsw inputProcessorSubmitterWrapper) Submit(
 // though is free to choose different policies by configuring
 // the Experiment, Submitter, and Saver fields properly.
 func (ip *InputProcessor) Run(ctx context.Context) error {
+	_, err := ip.run(ctx)
+	return err
+}
+
+// These are the reasons why run could stop.
+const (
+	stopNormal = (1 << iota)
+	stopMaxRuntime
+)
+
+// run is like Run but, in addition to returning an error, it
+// also returns the reason why we stopped.
+func (ip *InputProcessor) run(ctx context.Context) (int, error) {
 	start := time.Now()
 	for idx, url := range ip.Inputs {
 		if ip.MaxRuntime > 0 && time.Since(start) > ip.MaxRuntime {
-			atomic.AddInt32(&ip.terminatedByMaxRuntime, 1)
-			return nil
+			return stopMaxRuntime, nil
 		}
 		input := url.URL
 		meas, err := ip.Experiment.MeasureWithContext(ctx, idx, input)
 		if err != nil {
-			return err
+			return 0, err
 		}
 		meas.AddAnnotations(ip.Annotations)
 		meas.Options = ip.Options
 		err = ip.Submitter.Submit(ctx, idx, meas)
 		if err != nil {
-			return err
+			return 0, err
 		}
 		// Note: must be after submission because submission modifies
 		// the measurement to include the report ID.
 		err = ip.Saver.SaveMeasurement(idx, meas)
 		if err != nil {
-			return err
+			return 0, err
 		}
 	}
-	return nil
+	return stopNormal, nil
 }
diff --git a/internal/engine/inputprocessor_test.go b/internal/engine/inputprocessor_test.go
index 461c3bb..abb2beb 100644
--- a/internal/engine/inputprocessor_test.go
+++ b/internal/engine/inputprocessor_test.go
@@ -150,10 +150,11 @@ func TestInputProcessorGood(t *testing.T) {
 		Submitter: NewInputProcessorSubmitterWrapper(submitter),
 	}
 	ctx := context.Background()
-	if err := ip.Run(ctx); err != nil {
+	reason, err := ip.run(ctx)
+	if err != nil {
 		t.Fatal(err)
 	}
-	if ip.terminatedByMaxRuntime > 0 {
+	if reason != stopNormal {
 		t.Fatal("terminated by max runtime!?")
 	}
 	if len(fipe.M) != 2 || len(saver.M) != 2 || len(submitter.M) != 2 {
@@ -192,10 +193,11 @@ func TestInputProcessorMaxRuntime(t *testing.T) {
 		Submitter:  NewInputProcessorSubmitterWrapper(submitter),
 	}
 	ctx := context.Background()
-	if err := ip.Run(ctx); err != nil {
+	reason, err := ip.run(ctx)
+	if err != nil {
 		t.Fatal(err)
 	}
-	if ip.terminatedByMaxRuntime <= 0 {
+	if reason != stopMaxRuntime {
 		t.Fatal("not terminated by max runtime")
 	}
 }
diff --git a/internal/engine/internal/fsx/fsx_test.go b/internal/engine/internal/fsx/fsx_test.go
deleted file mode 100644
index e38da71..0000000
--- a/internal/engine/internal/fsx/fsx_test.go
+++ /dev/null
@@ -1,76 +0,0 @@
-package fsx_test
-
-import (
-	"errors"
-	"io/fs"
-	"os"
-	"sync/atomic"
-	"syscall"
-	"testing"
-
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/fsx"
-)
-
-var StateBaseDir = "./testdata/"
-
-type FailingStatFS struct {
-	CloseCount *int32
-}
-
-type FailingStatFile struct {
-	CloseCount *int32
-}
-
-var errStatFailed = errors.New("stat failed")
-
-func (FailingStatFile) Stat() (os.FileInfo, error) {
-	return nil, errStatFailed
-}
-
-func (f FailingStatFS) Open(pathname string) (fs.File, error) {
-	return FailingStatFile(f), nil
-}
-
-func (fs FailingStatFile) Close() error {
-	if fs.CloseCount != nil {
-		atomic.AddInt32(fs.CloseCount, 1)
-	}
-	return nil
-}
-
-func (FailingStatFile) Read([]byte) (int, error) {
-	return 0, nil
-}
-
-func TestOpenWithFailingStat(t *testing.T) {
-	var count int32
-	_, err := fsx.OpenWithFS(FailingStatFS{CloseCount: &count}, StateBaseDir+"testfile.txt")
-	if !errors.Is(err, errStatFailed) {
-		t.Errorf("expected error with invalid FS: %+v", err)
-	}
-	if count != 1 {
-		t.Error("expected counter to be equal to 1")
-	}
-}
-
-func TestOpenNonexistentFile(t *testing.T) {
-	_, err := fsx.Open(StateBaseDir + "invalidtestfile.txt")
-	if !errors.Is(err, syscall.ENOENT) {
-		t.Errorf("not the error we expected")
-	}
-}
-
-func TestOpenDirectoryShouldFail(t *testing.T) {
-	_, err := fsx.Open(StateBaseDir)
-	if !errors.Is(err, syscall.EISDIR) {
-		t.Fatalf("not the error we expected: %+v", err)
-	}
-}
-
-func TestOpeningExistingFileShouldWork(t *testing.T) {
-	file, err := fsx.Open(StateBaseDir + "testfile.txt")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer file.Close()
-}
diff --git a/internal/engine/internal/mockable/mockable.go b/internal/engine/internal/mockable/mockable.go
index 60f256a..f63f50d 100644
--- a/internal/engine/internal/mockable/mockable.go
+++ b/internal/engine/internal/mockable/mockable.go
@@ -6,9 +6,9 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 // Session allows to mock sessions.
@@ -67,7 +67,7 @@ func (sess *Session) FetchURLList(
 
 // KeyValueStore returns the configured key-value store.
 func (sess *Session) KeyValueStore() model.KeyValueStore {
-	return kvstore.NewMemoryKeyValueStore()
+	return &kvstore.Memory{}
 }
 
 // Logger implements ExperimentSession.Logger
diff --git a/internal/engine/internal/sessionresolver/integration_test.go b/internal/engine/internal/sessionresolver/integration_test.go
index 52d9fe0..d9c729a 100644
--- a/internal/engine/internal/sessionresolver/integration_test.go
+++ b/internal/engine/internal/sessionresolver/integration_test.go
@@ -5,13 +5,16 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/sessionresolver"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 func TestSessionResolverGood(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skip test in short mode")
 	}
-	reso := &sessionresolver.Resolver{}
+	reso := &sessionresolver.Resolver{
+		KVStore: &kvstore.Memory{},
+	}
 	defer reso.CloseIdleConnections()
 	if reso.Network() != "sessionresolver" {
 		t.Fatal("unexpected Network")
diff --git a/internal/engine/internal/sessionresolver/memkvstore.go b/internal/engine/internal/sessionresolver/memkvstore.go
deleted file mode 100644
index daacc1c..0000000
--- a/internal/engine/internal/sessionresolver/memkvstore.go
+++ /dev/null
@@ -1,43 +0,0 @@
-package sessionresolver
-
-import (
-	"errors"
-	"fmt"
-	"sync"
-)
-
-func (r *Resolver) kvstore() KVStore {
-	defer r.mu.Unlock()
-	r.mu.Lock()
-	if r.KVStore == nil {
-		r.KVStore = &memkvstore{}
-	}
-	return r.KVStore
-}
-
-var errMemkvstoreNotFound = errors.New("memkvstore: not found")
-
-type memkvstore struct {
-	m  map[string][]byte
-	mu sync.Mutex
-}
-
-func (kvs *memkvstore) Get(key string) ([]byte, error) {
-	defer kvs.mu.Unlock()
-	kvs.mu.Lock()
-	out, good := kvs.m[key]
-	if !good {
-		return nil, fmt.Errorf("%w: %s", errMemkvstoreNotFound, key)
-	}
-	return out, nil
-}
-
-func (kvs *memkvstore) Set(key string, value []byte) error {
-	defer kvs.mu.Unlock()
-	kvs.mu.Lock()
-	if kvs.m == nil {
-		kvs.m = make(map[string][]byte)
-	}
-	kvs.m[key] = value
-	return nil
-}
diff --git a/internal/engine/internal/sessionresolver/memkvstore_test.go b/internal/engine/internal/sessionresolver/memkvstore_test.go
deleted file mode 100644
index b924ef4..0000000
--- a/internal/engine/internal/sessionresolver/memkvstore_test.go
+++ /dev/null
@@ -1,47 +0,0 @@
-package sessionresolver
-
-import (
-	"errors"
-	"testing"
-
-	"github.com/google/go-cmp/cmp"
-)
-
-func TestKVStoreCustom(t *testing.T) {
-	kvs := &memkvstore{}
-	reso := &Resolver{KVStore: kvs}
-	o := reso.kvstore()
-	if o != kvs {
-		t.Fatal("not the kvstore we expected")
-	}
-}
-
-func TestMemkvstoreGetNotFound(t *testing.T) {
-	reso := &Resolver{}
-	key := "antani"
-	out, err := reso.kvstore().Get(key)
-	if !errors.Is(err, errMemkvstoreNotFound) {
-		t.Fatal("not the error we expected", err)
-	}
-	if out != nil {
-		t.Fatal("expected nil here")
-	}
-}
-
-func TestMemkvstoreRoundTrip(t *testing.T) {
-	reso := &Resolver{}
-	key := []string{"antani", "mascetti"}
-	value := [][]byte{[]byte(`mascetti`), []byte(`antani`)}
-	for idx := 0; idx < 2; idx++ {
-		if err := reso.kvstore().Set(key[idx], value[idx]); err != nil {
-			t.Fatal(err)
-		}
-		out, err := reso.kvstore().Get(key[idx])
-		if err != nil {
-			t.Fatal(err)
-		}
-		if diff := cmp.Diff(value[idx], out); diff != "" {
-			t.Fatal(diff)
-		}
-	}
-}
diff --git a/internal/engine/internal/sessionresolver/sessionresolver.go b/internal/engine/internal/sessionresolver/sessionresolver.go
index 8e7be14..9180cd2 100644
--- a/internal/engine/internal/sessionresolver/sessionresolver.go
+++ b/internal/engine/internal/sessionresolver/sessionresolver.go
@@ -33,9 +33,9 @@ import (
 	"sync"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/multierror"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/bytecounter"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/multierror"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // Resolver is the session resolver. Resolver will try to use
@@ -45,6 +45,9 @@ import (
 // and therefore we can generally give preference to underlying
 // DoT/DoH resolvers that work better.
 //
+// Make sure you fill the mandatory fields (indicated below)
+// before using this data structure.
+//
 // You MUST NOT modify public fields of this structure once it
 // has been created, because that MAY lead to data races.
 //
@@ -57,10 +60,9 @@ type Resolver struct {
 	// field is not set, then we won't count the bytes.
 	ByteCounter *bytecounter.Counter
 
-	// KVStore is the optional key-value store where you
+	// KVStore is the MANDATORY key-value store where you
 	// want us to write statistics about which resolver is
-	// working better in your network. If this field is
-	// not set, then we'll use a in-memory store.
+	// working better in your network.
 	KVStore KVStore
 
 	// Logger is the optional logger you want us to use
diff --git a/internal/engine/internal/sessionresolver/sessionresolver_test.go b/internal/engine/internal/sessionresolver/sessionresolver_test.go
index 8b46c1f..f62dd2f 100644
--- a/internal/engine/internal/sessionresolver/sessionresolver_test.go
+++ b/internal/engine/internal/sessionresolver/sessionresolver_test.go
@@ -6,11 +6,12 @@ import (
 	"net"
 	"net/url"
 	"strings"
-	"sync/atomic"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/multierror"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/multierror"
 )
 
 func TestNetworkWorks(t *testing.T) {
@@ -30,7 +31,7 @@ func TestAddressWorks(t *testing.T) {
 func TestTypicalUsageWithFailure(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel() // fail immediately
-	reso := &Resolver{}
+	reso := &Resolver{KVStore: &kvstore.Memory{}}
 	addrs, err := reso.LookupHost(ctx, "ooni.org")
 	if !errors.Is(err, ErrLookupHost) {
 		t.Fatal("not the error we expected", err)
@@ -82,6 +83,7 @@ func TestTypicalUsageWithSuccess(t *testing.T) {
 	expected := []string{"8.8.8.8", "8.8.4.4"}
 	ctx := context.Background()
 	reso := &Resolver{
+		KVStore: &kvstore.Memory{},
 		dnsClientMaker: &fakeDNSClientMaker{
 			reso: &FakeResolver{Data: expected},
 		},
@@ -252,7 +254,7 @@ func TestMaybeConfusionManyEntries(t *testing.T) {
 
 func TestResolverWorksWithProxy(t *testing.T) {
 	var (
-		works      int32
+		works      = &atomicx.Int64{}
 		startuperr = make(chan error)
 		listench   = make(chan net.Listener)
 		done       = make(chan interface{})
@@ -273,7 +275,7 @@ func TestResolverWorksWithProxy(t *testing.T) {
 				// shutdown by the main goroutine.
 				return
 			}
-			atomic.AddInt32(&works, 1)
+			works.Add(1)
 			conn.Close()
 		}
 	}()
@@ -283,10 +285,13 @@ func TestResolverWorksWithProxy(t *testing.T) {
 	}
 	listener := <-listench
 	// use the proxy
-	reso := &Resolver{ProxyURL: &url.URL{
-		Scheme: "socks5",
-		Host:   listener.Addr().String(),
-	}}
+	reso := &Resolver{
+		ProxyURL: &url.URL{
+			Scheme: "socks5",
+			Host:   listener.Addr().String(),
+		},
+		KVStore: &kvstore.Memory{},
+	}
 	ctx := context.Background()
 	addrs, err := reso.LookupHost(ctx, "ooni.org")
 	// cleanly shutdown the listener
@@ -299,7 +304,7 @@ func TestResolverWorksWithProxy(t *testing.T) {
 	if addrs != nil {
 		t.Fatal("expected nil addrs")
 	}
-	if works < 1 {
+	if works.Load() < 1 {
 		t.Fatal("expected to see a positive number of entries here")
 	}
 }
diff --git a/internal/engine/internal/sessionresolver/state.go b/internal/engine/internal/sessionresolver/state.go
index b725f9a..19970c3 100644
--- a/internal/engine/internal/sessionresolver/state.go
+++ b/internal/engine/internal/sessionresolver/state.go
@@ -18,9 +18,15 @@ type resolverinfo struct {
 	Score float64
 }
 
+// ErrNilKVStore indicates that the KVStore is nil.
+var ErrNilKVStore = errors.New("sessionresolver: kvstore is nil")
+
 // readstate reads the resolver state from disk
 func (r *Resolver) readstate() ([]*resolverinfo, error) {
-	data, err := r.kvstore().Get(storekey)
+	if r.KVStore == nil {
+		return nil, ErrNilKVStore
+	}
+	data, err := r.KVStore.Get(storekey)
 	if err != nil {
 		return nil, err
 	}
@@ -85,9 +91,12 @@ func (r *Resolver) readstatedefault() []*resolverinfo {
 
 // writestate writes the state on the kvstore.
 func (r *Resolver) writestate(ri []*resolverinfo) error {
+	if r.KVStore == nil {
+		return ErrNilKVStore
+	}
 	data, err := r.getCodec().Encode(ri)
 	if err != nil {
 		return err
 	}
-	return r.kvstore().Set(storekey, data)
+	return r.KVStore.Set(storekey, data)
 }
diff --git a/internal/engine/internal/sessionresolver/state_test.go b/internal/engine/internal/sessionresolver/state_test.go
index 168ee5c..0046325 100644
--- a/internal/engine/internal/sessionresolver/state_test.go
+++ b/internal/engine/internal/sessionresolver/state_test.go
@@ -3,12 +3,25 @@ package sessionresolver
 import (
 	"errors"
 	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
-func TestReadStateNothingInKVStore(t *testing.T) {
-	reso := &Resolver{KVStore: &memkvstore{}}
+func TestReadStateNoKVStore(t *testing.T) {
+	reso := &Resolver{}
 	out, err := reso.readstate()
-	if !errors.Is(err, errMemkvstoreNotFound) {
+	if !errors.Is(err, ErrNilKVStore) {
+		t.Fatal("not the error we expected", err)
+	}
+	if out != nil {
+		t.Fatal("expected nil here")
+	}
+}
+
+func TestReadStateNothingInKVStore(t *testing.T) {
+	reso := &Resolver{KVStore: &kvstore.Memory{}}
+	out, err := reso.readstate()
+	if !errors.Is(err, kvstore.ErrNoSuchKey) {
 		t.Fatal("not the error we expected", err)
 	}
 	if out != nil {
@@ -19,7 +32,7 @@ func TestReadStateNothingInKVStore(t *testing.T) {
 func TestReadStateDecodeError(t *testing.T) {
 	errMocked := errors.New("mocked error")
 	reso := &Resolver{
-		KVStore: &memkvstore{},
+		KVStore: &kvstore.Memory{},
 		codec:   &FakeCodec{DecodeErr: errMocked},
 	}
 	if err := reso.KVStore.Set(storekey, []byte(`[]`)); err != nil {
@@ -35,9 +48,9 @@ func TestReadStateDecodeError(t *testing.T) {
 }
 
 func TestReadStateAndPruneReadStateError(t *testing.T) {
-	reso := &Resolver{KVStore: &memkvstore{}}
+	reso := &Resolver{KVStore: &kvstore.Memory{}}
 	out, err := reso.readstateandprune()
-	if !errors.Is(err, errMemkvstoreNotFound) {
+	if !errors.Is(err, kvstore.ErrNoSuchKey) {
 		t.Fatal("not the error we expected", err)
 	}
 	if out != nil {
@@ -46,7 +59,7 @@ func TestReadStateAndPruneReadStateError(t *testing.T) {
 }
 
 func TestReadStateAndPruneWithUnsupportedEntries(t *testing.T) {
-	reso := &Resolver{KVStore: &memkvstore{}}
+	reso := &Resolver{KVStore: &kvstore.Memory{}}
 	var in []*resolverinfo
 	in = append(in, &resolverinfo{})
 	if err := reso.writestate(in); err != nil {
@@ -62,7 +75,7 @@ func TestReadStateAndPruneWithUnsupportedEntries(t *testing.T) {
 }
 
 func TestReadStateDefaultWithMissingEntries(t *testing.T) {
-	reso := &Resolver{KVStore: &memkvstore{}}
+	reso := &Resolver{KVStore: &kvstore.Memory{}}
 	// let us simulate that we have just one entry here
 	existingURL := "https://dns.google/dns-query"
 	existingScore := 0.88
@@ -100,12 +113,27 @@ func TestReadStateDefaultWithMissingEntries(t *testing.T) {
 	}
 }
 
+func TestWriteStateNoKVStore(t *testing.T) {
+	reso := &Resolver{}
+	existingURL := "https://dns.google/dns-query"
+	existingScore := 0.88
+	var in []*resolverinfo
+	in = append(in, &resolverinfo{
+		URL:   existingURL,
+		Score: existingScore,
+	})
+	if err := reso.writestate(in); !errors.Is(err, ErrNilKVStore) {
+		t.Fatal("not the error we expected", err)
+	}
+}
+
 func TestWriteStateCannotSerialize(t *testing.T) {
 	errMocked := errors.New("mocked error")
 	reso := &Resolver{
 		codec: &FakeCodec{
 			EncodeErr: errMocked,
 		},
+		KVStore: &kvstore.Memory{},
 	}
 	existingURL := "https://dns.google/dns-query"
 	existingScore := 0.88
diff --git a/internal/engine/kvstore.go b/internal/engine/kvstore.go
index 2e20229..c744de6 100644
--- a/internal/engine/kvstore.go
+++ b/internal/engine/kvstore.go
@@ -1,13 +1,5 @@
 package engine
 
-import (
-	"bytes"
-	"os"
-	"path/filepath"
-
-	"github.com/rogpeppe/go-internal/lockedfile"
-)
-
 // KVStore is a simple, atomic key-value store. The user of
 // probe-engine should supply an implementation of this interface,
 // which will be used by probe-engine to store specific data.
@@ -15,30 +7,3 @@ type KVStore interface {
 	Get(key string) (value []byte, err error)
 	Set(key string, value []byte) (err error)
 }
-
-// FileSystemKVStore is a directory based KVStore
-type FileSystemKVStore struct {
-	basedir string
-}
-
-// NewFileSystemKVStore creates a new FileSystemKVStore.
-func NewFileSystemKVStore(basedir string) (kvs *FileSystemKVStore, err error) {
-	if err = os.MkdirAll(basedir, 0700); err == nil {
-		kvs = &FileSystemKVStore{basedir: basedir}
-	}
-	return
-}
-
-func (kvs *FileSystemKVStore) filename(key string) string {
-	return filepath.Join(kvs.basedir, key)
-}
-
-// Get returns the specified key's value
-func (kvs *FileSystemKVStore) Get(key string) ([]byte, error) {
-	return lockedfile.Read(kvs.filename(key))
-}
-
-// Set sets the value of a specific key
-func (kvs *FileSystemKVStore) Set(key string, value []byte) error {
-	return lockedfile.Write(kvs.filename(key), bytes.NewReader(value), 0600)
-}
diff --git a/internal/engine/kvstore/kvstore.go b/internal/engine/kvstore/kvstore.go
deleted file mode 100644
index c20334c..0000000
--- a/internal/engine/kvstore/kvstore.go
+++ /dev/null
@@ -1,44 +0,0 @@
-// Package kvstore contains key-value stores
-package kvstore
-
-import (
-	"errors"
-	"sync"
-)
-
-// MemoryKeyValueStore is an in-memory key-value store
-type MemoryKeyValueStore struct {
-	m  map[string][]byte
-	mu sync.Mutex
-}
-
-// NewMemoryKeyValueStore creates a new in-memory key-value store
-func NewMemoryKeyValueStore() *MemoryKeyValueStore {
-	return &MemoryKeyValueStore{
-		m: make(map[string][]byte),
-	}
-}
-
-// Get returns a key from the key value store
-func (kvs *MemoryKeyValueStore) Get(key string) ([]byte, error) {
-	var (
-		err   error
-		ok    bool
-		value []byte
-	)
-	kvs.mu.Lock()
-	defer kvs.mu.Unlock()
-	value, ok = kvs.m[key]
-	if !ok {
-		err = errors.New("no such key")
-	}
-	return value, err
-}
-
-// Set sets a key into the key value store
-func (kvs *MemoryKeyValueStore) Set(key string, value []byte) error {
-	kvs.mu.Lock()
-	defer kvs.mu.Unlock()
-	kvs.m[key] = value
-	return nil
-}
diff --git a/internal/engine/kvstore_test.go b/internal/engine/kvstore_test.go
deleted file mode 100644
index 75e48af..0000000
--- a/internal/engine/kvstore_test.go
+++ /dev/null
@@ -1,31 +0,0 @@
-package engine
-
-import (
-	"bytes"
-	"path/filepath"
-	"testing"
-)
-
-func TestKVStoreIntegration(t *testing.T) {
-	var (
-		err     error
-		kvstore KVStore
-	)
-	kvstore, err = NewFileSystemKVStore(
-		filepath.Join("testdata", "kvstore2"),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-	value := []byte("foobar")
-	if err := kvstore.Set("antani", value); err != nil {
-		t.Fatal(err)
-	}
-	ovalue, err := kvstore.Get("antani")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !bytes.Equal(ovalue, value) {
-		t.Fatal("invalid value")
-	}
-}
diff --git a/internal/engine/legacy/netx/dialid/dialid.go b/internal/engine/legacy/netx/dialid/dialid.go
index 6cfd464..6c5185b 100644
--- a/internal/engine/legacy/netx/dialid/dialid.go
+++ b/internal/engine/legacy/netx/dialid/dialid.go
@@ -3,12 +3,12 @@ package dialid
 import (
 	"context"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
 type contextkey struct{}
 
-var id = atomicx.NewInt64()
+var id = &atomicx.Int64{}
 
 // WithDialID returns a copy of ctx with DialID
 func WithDialID(ctx context.Context) context.Context {
diff --git a/internal/engine/legacy/netx/handlers/handlers.go b/internal/engine/legacy/netx/handlers/handlers.go
index 48f79b2..4ad7248 100644
--- a/internal/engine/legacy/netx/handlers/handlers.go
+++ b/internal/engine/legacy/netx/handlers/handlers.go
@@ -7,7 +7,7 @@ import (
 	"sync"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 type stdoutHandler struct{}
diff --git a/internal/engine/legacy/netx/oldhttptransport/tracetripper.go b/internal/engine/legacy/netx/oldhttptransport/tracetripper.go
index 8280d5f..baad6dd 100644
--- a/internal/engine/legacy/netx/oldhttptransport/tracetripper.go
+++ b/internal/engine/legacy/netx/oldhttptransport/tracetripper.go
@@ -10,7 +10,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/connid"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/dialid"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
@@ -28,7 +28,7 @@ type TraceTripper struct {
 // NewTraceTripper creates a new Transport.
 func NewTraceTripper(roundTripper http.RoundTripper) *TraceTripper {
 	return &TraceTripper{
-		readAllErrs:  atomicx.NewInt64(),
+		readAllErrs:  &atomicx.Int64{},
 		readAll:      ioutil.ReadAll,
 		roundTripper: roundTripper,
 	}
diff --git a/internal/engine/legacy/netx/transactionid/transactionid.go b/internal/engine/legacy/netx/transactionid/transactionid.go
index 91f5168..6fab055 100644
--- a/internal/engine/legacy/netx/transactionid/transactionid.go
+++ b/internal/engine/legacy/netx/transactionid/transactionid.go
@@ -4,12 +4,12 @@ package transactionid
 import (
 	"context"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
 type contextkey struct{}
 
-var id = atomicx.NewInt64()
+var id = &atomicx.Int64{}
 
 // WithTransactionID returns a copy of ctx with TransactionID
 func WithTransactionID(ctx context.Context) context.Context {
diff --git a/internal/engine/legacy/oonitemplates/oonitemplates.go b/internal/engine/legacy/oonitemplates/oonitemplates.go
index 16e7277..cb7ba09 100644
--- a/internal/engine/legacy/oonitemplates/oonitemplates.go
+++ b/internal/engine/legacy/oonitemplates/oonitemplates.go
@@ -20,11 +20,11 @@ import (
 	"time"
 
 	goptlib "git.torproject.org/pluggable-transports/goptlib.git"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/handlers"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"gitlab.com/yawning/obfs4.git/transports"
 	obfs4base "gitlab.com/yawning/obfs4.git/transports/base"
 )
@@ -37,7 +37,7 @@ type channelHandler struct {
 func newChannelHandler(ch chan<- modelx.Measurement) *channelHandler {
 	return &channelHandler{
 		ch:         ch,
-		lateWrites: atomicx.NewInt64(),
+		lateWrites: &atomicx.Int64{},
 	}
 }
 
diff --git a/internal/engine/netx/bytecounter/bytecounter.go b/internal/engine/netx/bytecounter/bytecounter.go
index 426b874..b1c9a02 100644
--- a/internal/engine/netx/bytecounter/bytecounter.go
+++ b/internal/engine/netx/bytecounter/bytecounter.go
@@ -1,6 +1,6 @@
 package bytecounter
 
-import "github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+import "github.com/ooni/probe-cli/v3/internal/atomicx"
 
 // Counter counts bytes sent and received.
 type Counter struct {
@@ -10,7 +10,7 @@ type Counter struct {
 
 // New creates a new Counter.
 func New() *Counter {
-	return &Counter{Received: atomicx.NewInt64(), Sent: atomicx.NewInt64()}
+	return &Counter{Received: &atomicx.Int64{}, Sent: &atomicx.Int64{}}
 }
 
 // CountBytesSent adds count to the bytes sent counter.
diff --git a/internal/engine/netx/netx.go b/internal/engine/netx/netx.go
index 25f2365..5a2175a 100644
--- a/internal/engine/netx/netx.go
+++ b/internal/engine/netx/netx.go
@@ -39,7 +39,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/resolver"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/selfcensor"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // Logger is the logger assumed by this package
diff --git a/internal/engine/netx/resolver/bogon.go b/internal/engine/netx/resolver/bogon.go
index 2b4fe50..8103cc3 100644
--- a/internal/engine/netx/resolver/bogon.go
+++ b/internal/engine/netx/resolver/bogon.go
@@ -5,7 +5,7 @@ import (
 	"net"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 var privateIPBlocks []*net.IPNet
diff --git a/internal/engine/netx/resolver/fake_test.go b/internal/engine/netx/resolver/fake_test.go
index e406381..576e738 100644
--- a/internal/engine/netx/resolver/fake_test.go
+++ b/internal/engine/netx/resolver/fake_test.go
@@ -6,7 +6,7 @@ import (
 	"net"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
 type FakeDialer struct {
@@ -109,11 +109,11 @@ type FakeResolver struct {
 }
 
 func NewFakeResolverThatFails() FakeResolver {
-	return FakeResolver{NumFailures: atomicx.NewInt64(), Err: errNotFound}
+	return FakeResolver{NumFailures: &atomicx.Int64{}, Err: errNotFound}
 }
 
 func NewFakeResolverWithResult(r []string) FakeResolver {
-	return FakeResolver{NumFailures: atomicx.NewInt64(), Result: r}
+	return FakeResolver{NumFailures: &atomicx.Int64{}, Result: r}
 }
 
 var errNotFound = &net.DNSError{
diff --git a/internal/engine/netx/resolver/serial.go b/internal/engine/netx/resolver/serial.go
index 6f82caa..6844df7 100644
--- a/internal/engine/netx/resolver/serial.go
+++ b/internal/engine/netx/resolver/serial.go
@@ -6,7 +6,7 @@ import (
 	"net"
 
 	"github.com/miekg/dns"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
 // RoundTripper represents an abstract DNS transport.
@@ -38,7 +38,7 @@ func NewSerialResolver(t RoundTripper) SerialResolver {
 	return SerialResolver{
 		Encoder:     MiekgEncoder{},
 		Decoder:     MiekgDecoder{},
-		NumTimeouts: atomicx.NewInt64(),
+		NumTimeouts: &atomicx.Int64{},
 		Txp:         t,
 	}
 }
diff --git a/internal/engine/netx/selfcensor/selfcensor.go b/internal/engine/netx/selfcensor/selfcensor.go
index 406ded4..bbe0147 100644
--- a/internal/engine/netx/selfcensor/selfcensor.go
+++ b/internal/engine/netx/selfcensor/selfcensor.go
@@ -31,7 +31,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
 // Spec indicates what self censorship techniques to implement.
@@ -61,8 +61,8 @@ type Spec struct {
 }
 
 var (
-	attempts *atomicx.Int64 = atomicx.NewInt64()
-	enabled  *atomicx.Int64 = atomicx.NewInt64()
+	attempts *atomicx.Int64 = &atomicx.Int64{}
+	enabled  *atomicx.Int64 = &atomicx.Int64{}
 	mu       sync.Mutex
 	spec     *Spec
 )
diff --git a/internal/engine/ooapi/README.md b/internal/engine/ooapi/README.md
deleted file mode 100644
index 63de899..0000000
--- a/internal/engine/ooapi/README.md
+++ /dev/null
@@ -1,5 +0,0 @@
-# Package ./internal/engine/ooapi
-
-Automatically generated API clients for speaking with OONI servers.
-
-Please, run `go doc ./internal/engine/ooapi` to see API documentation.
diff --git a/internal/engine/ooapi/kvstore_test.go b/internal/engine/ooapi/kvstore_test.go
deleted file mode 100644
index 625c9d7..0000000
--- a/internal/engine/ooapi/kvstore_test.go
+++ /dev/null
@@ -1,34 +0,0 @@
-package ooapi
-
-import (
-	"errors"
-	"fmt"
-	"sync"
-)
-
-var errMemkvstoreNotFound = errors.New("memkvstore: not found")
-
-type MemKVStore struct {
-	m  map[string][]byte
-	mu sync.Mutex
-}
-
-func (kvs *MemKVStore) Get(key string) ([]byte, error) {
-	defer kvs.mu.Unlock()
-	kvs.mu.Lock()
-	out, good := kvs.m[key]
-	if !good {
-		return nil, fmt.Errorf("%w: %s", errMemkvstoreNotFound, key)
-	}
-	return out, nil
-}
-
-func (kvs *MemKVStore) Set(key string, value []byte) error {
-	defer kvs.mu.Unlock()
-	kvs.mu.Lock()
-	if kvs.m == nil {
-		kvs.m = make(map[string][]byte)
-	}
-	kvs.m[key] = value
-	return nil
-}
diff --git a/internal/engine/probeservices/checkreportid_test.go b/internal/engine/probeservices/checkreportid_test.go
index d3fce64..631713d 100644
--- a/internal/engine/probeservices/checkreportid_test.go
+++ b/internal/engine/probeservices/checkreportid_test.go
@@ -7,10 +7,10 @@ import (
 	"testing"
 
 	"github.com/apex/log"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpx"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 func TestCheckReportIDWorkingAsIntended(t *testing.T) {
@@ -21,9 +21,9 @@ func TestCheckReportIDWorkingAsIntended(t *testing.T) {
 			Logger:     log.Log,
 			UserAgent:  "miniooni/0.1.0-dev",
 		},
-		LoginCalls:    atomicx.NewInt64(),
-		RegisterCalls: atomicx.NewInt64(),
-		StateFile:     probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore()),
+		LoginCalls:    &atomicx.Int64{},
+		RegisterCalls: &atomicx.Int64{},
+		StateFile:     probeservices.NewStateFile(&kvstore.Memory{}),
 	}
 	reportID := `20201209T052225Z_urlgetter_IT_30722_n1_E1VUhMz08SEkgYFU`
 	ctx := context.Background()
@@ -44,9 +44,9 @@ func TestCheckReportIDWorkingWithCancelledContext(t *testing.T) {
 			Logger:     log.Log,
 			UserAgent:  "miniooni/0.1.0-dev",
 		},
-		LoginCalls:    atomicx.NewInt64(),
-		RegisterCalls: atomicx.NewInt64(),
-		StateFile:     probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore()),
+		LoginCalls:    &atomicx.Int64{},
+		RegisterCalls: &atomicx.Int64{},
+		StateFile:     probeservices.NewStateFile(&kvstore.Memory{}),
 	}
 	reportID := `20201209T052225Z_urlgetter_IT_30722_n1_E1VUhMz08SEkgYFU`
 	ctx, cancel := context.WithCancel(context.Background())
diff --git a/internal/engine/probeservices/measurementmeta_test.go b/internal/engine/probeservices/measurementmeta_test.go
index c777d5d..6613bf0 100644
--- a/internal/engine/probeservices/measurementmeta_test.go
+++ b/internal/engine/probeservices/measurementmeta_test.go
@@ -8,10 +8,10 @@ import (
 	"testing"
 
 	"github.com/apex/log"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpx"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 func TestGetMeasurementMetaWorkingAsIntended(t *testing.T) {
@@ -22,9 +22,9 @@ func TestGetMeasurementMetaWorkingAsIntended(t *testing.T) {
 			Logger:     log.Log,
 			UserAgent:  "miniooni/0.1.0-dev",
 		},
-		LoginCalls:    atomicx.NewInt64(),
-		RegisterCalls: atomicx.NewInt64(),
-		StateFile:     probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore()),
+		LoginCalls:    &atomicx.Int64{},
+		RegisterCalls: &atomicx.Int64{},
+		StateFile:     probeservices.NewStateFile(&kvstore.Memory{}),
 	}
 	config := probeservices.MeasurementMetaConfig{
 		ReportID: `20201209T052225Z_urlgetter_IT_30722_n1_E1VUhMz08SEkgYFU`,
@@ -90,9 +90,9 @@ func TestGetMeasurementMetaWorkingWithCancelledContext(t *testing.T) {
 			Logger:     log.Log,
 			UserAgent:  "miniooni/0.1.0-dev",
 		},
-		LoginCalls:    atomicx.NewInt64(),
-		RegisterCalls: atomicx.NewInt64(),
-		StateFile:     probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore()),
+		LoginCalls:    &atomicx.Int64{},
+		RegisterCalls: &atomicx.Int64{},
+		StateFile:     probeservices.NewStateFile(&kvstore.Memory{}),
 	}
 	config := probeservices.MeasurementMetaConfig{
 		ReportID: `20201209T052225Z_urlgetter_IT_30722_n1_E1VUhMz08SEkgYFU`,
diff --git a/internal/engine/probeservices/probeservices.go b/internal/engine/probeservices/probeservices.go
index ecbecdc..3a8b477 100644
--- a/internal/engine/probeservices/probeservices.go
+++ b/internal/engine/probeservices/probeservices.go
@@ -28,7 +28,7 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 )
@@ -98,8 +98,8 @@ func NewClient(sess Session, endpoint model.Service) (*Client, error) {
 			ProxyURL:   sess.ProxyURL(),
 			UserAgent:  sess.UserAgent(),
 		},
-		LoginCalls:    atomicx.NewInt64(),
-		RegisterCalls: atomicx.NewInt64(),
+		LoginCalls:    &atomicx.Int64{},
+		RegisterCalls: &atomicx.Int64{},
 		StateFile:     NewStateFile(sess.KeyValueStore()),
 	}
 	switch endpoint.Type {
diff --git a/internal/engine/probeservices/register.go b/internal/engine/probeservices/register.go
index 44dd16a..7b2c31e 100644
--- a/internal/engine/probeservices/register.go
+++ b/internal/engine/probeservices/register.go
@@ -3,7 +3,7 @@ package probeservices
 import (
 	"context"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/randx"
+	"github.com/ooni/probe-cli/v3/internal/randx"
 )
 
 type registerRequest struct {
diff --git a/internal/engine/probeservices/statefile_test.go b/internal/engine/probeservices/statefile_test.go
index d274fbf..272b798 100644
--- a/internal/engine/probeservices/statefile_test.go
+++ b/internal/engine/probeservices/statefile_test.go
@@ -7,8 +7,8 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
 )
 
 func TestStateAuth(t *testing.T) {
@@ -67,7 +67,7 @@ func TestStateCredentials(t *testing.T) {
 func TestStateFileMemoryIntegration(t *testing.T) {
 	// Does the StateFile have the property that we can write
 	// values into it and then read again the same files?
-	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	sf := probeservices.NewStateFile(&kvstore.Memory{})
 	s := probeservices.State{
 		Expire:   time.Now(),
 		Password: "xy",
@@ -85,7 +85,7 @@ func TestStateFileMemoryIntegration(t *testing.T) {
 }
 
 func TestStateFileSetMarshalError(t *testing.T) {
-	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	sf := probeservices.NewStateFile(&kvstore.Memory{})
 	s := probeservices.State{
 		Expire:   time.Now(),
 		Password: "xy",
@@ -102,7 +102,7 @@ func TestStateFileSetMarshalError(t *testing.T) {
 }
 
 func TestStateFileGetKVStoreGetError(t *testing.T) {
-	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	sf := probeservices.NewStateFile(&kvstore.Memory{})
 	expected := errors.New("mocked error")
 	failingfunc := func(string) ([]byte, error) {
 		return nil, expected
@@ -126,7 +126,7 @@ func TestStateFileGetKVStoreGetError(t *testing.T) {
 }
 
 func TestStateFileGetUnmarshalError(t *testing.T) {
-	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	sf := probeservices.NewStateFile(&kvstore.Memory{})
 	if err := sf.Set(probeservices.State{}); err != nil {
 		t.Fatal(err)
 	}
diff --git a/internal/engine/session.go b/internal/engine/session.go
index 11e42b9..6db35c2 100644
--- a/internal/engine/session.go
+++ b/internal/engine/session.go
@@ -10,16 +10,16 @@ import (
 	"os"
 	"sync"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/geolocate"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/platform"
 	"github.com/ooni/probe-cli/v3/internal/engine/internal/sessionresolver"
-	"github.com/ooni/probe-cli/v3/internal/engine/kvstore"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/bytecounter"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
 	"github.com/ooni/probe-cli/v3/internal/engine/tunnel"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/platform"
 	"github.com/ooni/probe-cli/v3/internal/version"
 )
 
@@ -52,7 +52,7 @@ type Session struct {
 	availableTestHelpers     map[string][]model.Service
 	byteCounter              *bytecounter.Counter
 	httpDefaultTransport     netx.HTTPRoundTripper
-	kvStore                  model.KeyValueStore
+	kvStore                  KVStore
 	location                 *geolocate.Results
 	logger                   model.Logger
 	proxyURL                 *url.URL
@@ -142,7 +142,7 @@ func NewSession(ctx context.Context, config SessionConfig) (*Session, error) {
 		return nil, errors.New("SoftwareVersion is empty")
 	}
 	if config.KVStore == nil {
-		config.KVStore = kvstore.NewMemoryKeyValueStore()
+		config.KVStore = &kvstore.Memory{}
 	}
 	// Implementation note: if config.TempDir is empty, then Go will
 	// use the temporary directory on the current system. This should
@@ -157,7 +157,7 @@ func NewSession(ctx context.Context, config SessionConfig) (*Session, error) {
 		byteCounter:             bytecounter.New(),
 		kvStore:                 config.KVStore,
 		logger:                  config.Logger,
-		queryProbeServicesCount: atomicx.NewInt64(),
+		queryProbeServicesCount: &atomicx.Int64{},
 		softwareName:            config.SoftwareName,
 		softwareVersion:         config.SoftwareVersion,
 		tempDir:                 tempDir,
diff --git a/internal/engine/submitter_test.go b/internal/engine/submitter_test.go
index d436856..a2f0795 100644
--- a/internal/engine/submitter_test.go
+++ b/internal/engine/submitter_test.go
@@ -3,10 +3,10 @@ package engine
 import (
 	"context"
 	"errors"
-	"sync/atomic"
 	"testing"
 
 	"github.com/apex/log"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 )
 
@@ -28,12 +28,14 @@ func TestSubmitterNotEnabled(t *testing.T) {
 }
 
 type FakeSubmitter struct {
-	Calls uint32
+	Calls *atomicx.Int64
 	Error error
 }
 
 func (fs *FakeSubmitter) Submit(ctx context.Context, m *model.Measurement) error {
-	atomic.AddUint32(&fs.Calls, 1)
+	if fs.Calls != nil {
+		fs.Calls.Add(1)
+	}
 	return fs.Error
 }
 
@@ -68,7 +70,10 @@ func TestNewSubmitterFails(t *testing.T) {
 func TestNewSubmitterWithFailedSubmission(t *testing.T) {
 	expected := errors.New("mocked error")
 	ctx := context.Background()
-	fakeSubmitter := &FakeSubmitter{Error: expected}
+	fakeSubmitter := &FakeSubmitter{
+		Calls: &atomicx.Int64{},
+		Error: expected,
+	}
 	submitter, err := NewSubmitter(ctx, SubmitterConfig{
 		Enabled: true,
 		Logger:  log.Log,
@@ -82,7 +87,7 @@ func TestNewSubmitterWithFailedSubmission(t *testing.T) {
 	if !errors.Is(err, expected) {
 		t.Fatalf("not the error we expected: %+v", err)
 	}
-	if fakeSubmitter.Calls != 1 {
+	if fakeSubmitter.Calls.Load() != 1 {
 		t.Fatal("unexpected number of calls")
 	}
 }
diff --git a/internal/engine/internal/fsx/fsx.go b/internal/fsx/fsx.go
similarity index 55%
rename from internal/engine/internal/fsx/fsx.go
rename to internal/fsx/fsx.go
index d5a8bf7..89b888f 100644
--- a/internal/engine/internal/fsx/fsx.go
+++ b/internal/fsx/fsx.go
@@ -1,4 +1,4 @@
-// Package fsx contains file system extension
+// Package fsx contains io/fs extensions.
 package fsx
 
 import (
@@ -8,13 +8,15 @@ import (
 	"syscall"
 )
 
-// Open is a wrapper for os.Open that ensures that we're opening a file.
-func Open(pathname string) (fs.File, error) {
-	return OpenWithFS(filesystem{}, pathname)
+// OpenFile is a wrapper for os.OpenFile that ensures that
+// we're opening a file rather than a directory. If you are
+// opening a directory, this func will return an error.
+func OpenFile(pathname string) (fs.File, error) {
+	return openWithFS(filesystem{}, pathname)
 }
 
-// OpenWithFS is like Open but with explicit file system argument.
-func OpenWithFS(fs fs.FS, pathname string) (fs.File, error) {
+// openWithFS is like Open but with explicit file system argument.
+func openWithFS(fs fs.FS, pathname string) (fs.File, error) {
 	file, err := fs.Open(pathname)
 	if err != nil {
 		return nil, err
diff --git a/internal/fsx/fsx_test.go b/internal/fsx/fsx_test.go
new file mode 100644
index 0000000..787f30e
--- /dev/null
+++ b/internal/fsx/fsx_test.go
@@ -0,0 +1,84 @@
+package fsx
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"syscall"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+)
+
+// baseDir is the base directory we use for testing.
+var baseDir = "./testdata/"
+
+// failingStatFS is a fs.FS returning a file where stat() fails.
+type failingStatFS struct {
+	CloseCount *atomicx.Int64
+}
+
+// failingStatFile is a fs.File where stat() fails.
+type failingStatFile struct {
+	CloseCount *atomicx.Int64
+}
+
+// errStatFailed is the internal error indicating that stat() failed.
+var errStatFailed = errors.New("stat failed")
+
+// Stat is a stat implementation that fails.
+func (failingStatFile) Stat() (os.FileInfo, error) {
+	return nil, errStatFailed
+}
+
+// Open opens a fake file whose Stat fails.
+func (f failingStatFS) Open(pathname string) (fs.File, error) {
+	return failingStatFile(f), nil
+}
+
+// Close closes the failingStatFile.
+func (fs failingStatFile) Close() error {
+	if fs.CloseCount != nil {
+		fs.CloseCount.Add(1)
+	}
+	return nil
+}
+
+// Read implements fs.File.Read.
+func (failingStatFile) Read([]byte) (int, error) {
+	return 0, errors.New("shouldn't be called")
+}
+
+func TestOpenWithFailingStat(t *testing.T) {
+	count := &atomicx.Int64{}
+	_, err := openWithFS(
+		failingStatFS{CloseCount: count}, baseDir+"testfile.txt")
+	if !errors.Is(err, errStatFailed) {
+		t.Error("expected error with invalid FS", err)
+	}
+	if count.Load() != 1 {
+		t.Error("expected close counter to be equal to 1")
+	}
+}
+
+func TestOpenNonexistentFile(t *testing.T) {
+	_, err := OpenFile(baseDir + "invalidtestfile.txt")
+	if !errors.Is(err, syscall.ENOENT) {
+		t.Errorf("not the error we expected")
+	}
+}
+
+func TestOpenDirectoryShouldFail(t *testing.T) {
+	_, err := OpenFile(baseDir)
+	if !errors.Is(err, syscall.EISDIR) {
+		t.Fatalf("not the error we expected: %+v", err)
+	}
+}
+
+func TestOpeningExistingFileShouldWork(t *testing.T) {
+	file, err := OpenFile(baseDir + "testfile.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+}
diff --git a/internal/engine/internal/fsx/testdata/.gitignore b/internal/fsx/testdata/.gitignore
similarity index 100%
rename from internal/engine/internal/fsx/testdata/.gitignore
rename to internal/fsx/testdata/.gitignore
diff --git a/internal/engine/internal/fsx/testdata/testfile.txt b/internal/fsx/testdata/testfile.txt
similarity index 100%
rename from internal/engine/internal/fsx/testdata/testfile.txt
rename to internal/fsx/testdata/testfile.txt
diff --git a/internal/engine/humanizex/humanizex.go b/internal/humanize/humanizex.go
similarity index 57%
rename from internal/engine/humanizex/humanizex.go
rename to internal/humanize/humanizex.go
index a41aa77..5a5934b 100644
--- a/internal/engine/humanizex/humanizex.go
+++ b/internal/humanize/humanizex.go
@@ -1,14 +1,17 @@
-// Package humanizex is like dustin/go-humanize
-package humanizex
+// Package humanize is like dustin/go-humanize.
+package humanize
 
 import "fmt"
 
-// SI is like dustin/go-humanize.SI
+// SI is like dustin/go-humanize.SI but its implementation is
+// specially tailored for printing download speeds.
 func SI(value float64, unit string) string {
 	value, prefix := reduce(value)
 	return fmt.Sprintf("%3.0f %s%s", value, prefix, unit)
 }
 
+// reduce reduces value to a base value and a unit prefix. For
+// example, reduce(1055) returns (1.055, "k").
 func reduce(value float64) (float64, string) {
 	if value < 1e03 {
 		return value, " "
diff --git a/internal/humanize/humanizex_test.go b/internal/humanize/humanizex_test.go
new file mode 100644
index 0000000..c7286ac
--- /dev/null
+++ b/internal/humanize/humanizex_test.go
@@ -0,0 +1,30 @@
+package humanize
+
+import "testing"
+
+func TestGood(t *testing.T) {
+	if SI(128, "bit/s") != "128  bit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(1280, "bit/s") != "  1 kbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(12800, "bit/s") != " 13 kbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(128000, "bit/s") != "128 kbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(1280000, "bit/s") != "  1 Mbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(12800000, "bit/s") != " 13 Mbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(128000000, "bit/s") != "128 Mbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if SI(1280000000, "bit/s") != "  1 Gbit/s" {
+		t.Fatal("unexpected result")
+	}
+}
diff --git a/internal/kvstore/fs.go b/internal/kvstore/fs.go
new file mode 100644
index 0000000..483a625
--- /dev/null
+++ b/internal/kvstore/fs.go
@@ -0,0 +1,53 @@
+package kvstore
+
+import (
+	"bytes"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+
+	"github.com/rogpeppe/go-internal/lockedfile"
+)
+
+// FS is a file-system based KVStore.
+type FS struct {
+	basedir string
+}
+
+// NewFS creates a new kvstore.FileSystem.
+func NewFS(basedir string) (kvs *FS, err error) {
+	return newFileSystem(basedir, os.MkdirAll)
+}
+
+// osMkdirAll is the type of os.MkdirAll.
+type osMkdirAll func(path string, perm fs.FileMode) error
+
+// newFileSystem is like NewFileSystem with a customizable
+// osMkdirAll function for creating the kvstore dir.
+func newFileSystem(basedir string, mkdir osMkdirAll) (*FS, error) {
+	if err := mkdir(basedir, 0700); err != nil {
+		return nil, err
+	}
+	return &FS{basedir: basedir}, nil
+}
+
+// filename returns the filename for a given key.
+func (kvs *FS) filename(key string) string {
+	return filepath.Join(kvs.basedir, key)
+}
+
+// Get returns the specified key's value. In case of error, the
+// error type is such that errors.Is(err, ErrNoSuchKey).
+func (kvs *FS) Get(key string) ([]byte, error) {
+	data, err := lockedfile.Read(kvs.filename(key))
+	if err != nil {
+		return nil, fmt.Errorf("%w: %s", ErrNoSuchKey, err.Error())
+	}
+	return data, nil
+}
+
+// Set sets the value of a specific key.
+func (kvs *FS) Set(key string, value []byte) error {
+	return lockedfile.Write(kvs.filename(key), bytes.NewReader(value), 0600)
+}
diff --git a/internal/kvstore/fs_test.go b/internal/kvstore/fs_test.go
new file mode 100644
index 0000000..462e5cb
--- /dev/null
+++ b/internal/kvstore/fs_test.go
@@ -0,0 +1,67 @@
+package kvstore
+
+import (
+	"bytes"
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFileSystemGood(t *testing.T) {
+	dirpath := filepath.Join("testdata", "kvstore2")
+	if err := os.RemoveAll(dirpath); err != nil {
+		t.Fatal(err)
+	}
+	kvstore, err := NewFS(dirpath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	value := []byte("foobar")
+	if err := kvstore.Set("antani", value); err != nil {
+		t.Fatal(err)
+	}
+	ovalue, err := kvstore.Get("antani")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(ovalue, value) {
+		t.Fatal("invalid value")
+	}
+}
+
+func TestFileSystemNoSuchKey(t *testing.T) {
+	dirpath := filepath.Join("testdata", "kvstore2")
+	if err := os.RemoveAll(dirpath); err != nil {
+		t.Fatal(err)
+	}
+	kvstore, err := NewFS(dirpath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	value, err := kvstore.Get("antani")
+	if !errors.Is(err, ErrNoSuchKey) {
+		t.Fatal("not the error we expected", err)
+	}
+	if value != nil {
+		t.Fatal("expected nil value")
+	}
+}
+
+func TestFileSystemWithFailure(t *testing.T) {
+	expect := errors.New("mocked error")
+	mkdir := func(path string, perm fs.FileMode) error {
+		return expect
+	}
+	kvstore, err := newFileSystem(
+		filepath.Join("testdata", "kvstore2"),
+		mkdir,
+	)
+	if !errors.Is(err, expect) {
+		t.Fatal("not the error we expected", err)
+	}
+	if kvstore != nil {
+		t.Fatal("expected nil here")
+	}
+}
diff --git a/internal/kvstore/memory.go b/internal/kvstore/memory.go
new file mode 100644
index 0000000..9129e5e
--- /dev/null
+++ b/internal/kvstore/memory.go
@@ -0,0 +1,42 @@
+// Package kvstore contains key-value stores.
+package kvstore
+
+import (
+	"errors"
+	"sync"
+)
+
+// ErrNoSuchKey indicates that there's no value for the given key.
+var ErrNoSuchKey = errors.New("no such key")
+
+// Memory is an in-memory key-value store.
+type Memory struct {
+	// m is the underlying map.
+	m map[string][]byte
+
+	// mu provides mutual exclusion
+	mu sync.Mutex
+}
+
+// Get returns the specified key's value. In case of error, the
+// error type is such that errors.Is(err, ErrNoSuchKey).
+func (kvs *Memory) Get(key string) ([]byte, error) {
+	kvs.mu.Lock()
+	defer kvs.mu.Unlock()
+	value, ok := kvs.m[key]
+	if !ok {
+		return nil, ErrNoSuchKey
+	}
+	return value, nil
+}
+
+// Set sets a key into the key-value store
+func (kvs *Memory) Set(key string, value []byte) error {
+	kvs.mu.Lock()
+	defer kvs.mu.Unlock()
+	if kvs.m == nil {
+		kvs.m = make(map[string][]byte)
+	}
+	kvs.m[key] = value
+	return nil
+}
diff --git a/internal/engine/kvstore/kvstore_test.go b/internal/kvstore/memory_test.go
similarity index 81%
rename from internal/engine/kvstore/kvstore_test.go
rename to internal/kvstore/memory_test.go
index b8acfe7..dff34e0 100644
--- a/internal/engine/kvstore/kvstore_test.go
+++ b/internal/kvstore/memory_test.go
@@ -1,11 +1,14 @@
 package kvstore
 
-import "testing"
+import (
+	"errors"
+	"testing"
+)
 
 func TestNoSuchKey(t *testing.T) {
-	kvs := NewMemoryKeyValueStore()
+	kvs := &Memory{}
 	value, err := kvs.Get("nonexistent")
-	if err == nil {
+	if !errors.Is(err, ErrNoSuchKey) {
 		t.Fatal("expected an error here")
 	}
 	if value != nil {
@@ -14,7 +17,7 @@ func TestNoSuchKey(t *testing.T) {
 }
 
 func TestExistingKey(t *testing.T) {
-	kvs := NewMemoryKeyValueStore()
+	kvs := &Memory{}
 	if err := kvs.Set("antani", []byte("mascetti")); err != nil {
 		t.Fatal(err)
 	}
diff --git a/internal/engine/internal/multierror/multierror.go b/internal/multierror/multierror.go
similarity index 85%
rename from internal/engine/internal/multierror/multierror.go
rename to internal/multierror/multierror.go
index 2440633..560a56b 100644
--- a/internal/engine/internal/multierror/multierror.go
+++ b/internal/multierror/multierror.go
@@ -9,11 +9,14 @@ import (
 
 // Union is the logical union of several errors. The Union will
 // appear to be the Root error, except that it will actually
-// be possible to look deeper and see specific sub errors that
+// be possible to look deeper and see specific child errors that
 // occurred using errors.As and errors.Is.
 type Union struct {
+	// Children contains the underlying errors.
 	Children []error
-	Root     error
+
+	// Root is the root error.
+	Root error
 }
 
 // New creates a new Union error instance.
@@ -37,8 +40,8 @@ func (err *Union) AddWithPrefix(prefix string, child error) {
 	err.Add(fmt.Errorf("%s: %w", prefix, child))
 }
 
-// Is returns whether the Union error contains at least one child
-// error that is exactly the specified target error.
+// Is returns true (1) if the err.Root error is target or (2) if
+// any err.Children error is target.
 func (err Union) Is(target error) bool {
 	if errors.Is(err.Root, target) {
 		return true
diff --git a/internal/engine/internal/multierror/multierror_test.go b/internal/multierror/multierror_test.go
similarity index 96%
rename from internal/engine/internal/multierror/multierror_test.go
rename to internal/multierror/multierror_test.go
index bb973db..5dfaed9 100644
--- a/internal/engine/internal/multierror/multierror_test.go
+++ b/internal/multierror/multierror_test.go
@@ -8,7 +8,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/multierror"
+	"github.com/ooni/probe-cli/v3/internal/multierror"
 )
 
 func TestEmpty(t *testing.T) {
diff --git a/internal/engine/ooapi/apimodel/checkin.go b/internal/ooapi/apimodel/checkin.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/checkin.go
rename to internal/ooapi/apimodel/checkin.go
diff --git a/internal/engine/ooapi/apimodel/checkreportid.go b/internal/ooapi/apimodel/checkreportid.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/checkreportid.go
rename to internal/ooapi/apimodel/checkreportid.go
diff --git a/internal/engine/ooapi/apimodel/doc.go b/internal/ooapi/apimodel/doc.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/doc.go
rename to internal/ooapi/apimodel/doc.go
diff --git a/internal/engine/ooapi/apimodel/login.go b/internal/ooapi/apimodel/login.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/login.go
rename to internal/ooapi/apimodel/login.go
diff --git a/internal/engine/ooapi/apimodel/measurementmeta.go b/internal/ooapi/apimodel/measurementmeta.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/measurementmeta.go
rename to internal/ooapi/apimodel/measurementmeta.go
diff --git a/internal/engine/ooapi/apimodel/openreport.go b/internal/ooapi/apimodel/openreport.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/openreport.go
rename to internal/ooapi/apimodel/openreport.go
diff --git a/internal/engine/ooapi/apimodel/psiphonconfig.go b/internal/ooapi/apimodel/psiphonconfig.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/psiphonconfig.go
rename to internal/ooapi/apimodel/psiphonconfig.go
diff --git a/internal/engine/ooapi/apimodel/register.go b/internal/ooapi/apimodel/register.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/register.go
rename to internal/ooapi/apimodel/register.go
diff --git a/internal/engine/ooapi/apimodel/submitmeasurement.go b/internal/ooapi/apimodel/submitmeasurement.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/submitmeasurement.go
rename to internal/ooapi/apimodel/submitmeasurement.go
diff --git a/internal/engine/ooapi/apimodel/testhelpers.go b/internal/ooapi/apimodel/testhelpers.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/testhelpers.go
rename to internal/ooapi/apimodel/testhelpers.go
diff --git a/internal/engine/ooapi/apimodel/tortargets.go b/internal/ooapi/apimodel/tortargets.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/tortargets.go
rename to internal/ooapi/apimodel/tortargets.go
diff --git a/internal/engine/ooapi/apimodel/urls.go b/internal/ooapi/apimodel/urls.go
similarity index 100%
rename from internal/engine/ooapi/apimodel/urls.go
rename to internal/ooapi/apimodel/urls.go
diff --git a/internal/engine/ooapi/apis.go b/internal/ooapi/apis.go
similarity index 99%
rename from internal/engine/ooapi/apis.go
rename to internal/ooapi/apis.go
index cbb69ae..dfe60c9 100644
--- a/internal/engine/ooapi/apis.go
+++ b/internal/ooapi/apis.go
@@ -9,7 +9,7 @@ import (
 	"context"
 	"net/http"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 // simpleCheckReportIDAPI implements the CheckReportID API.
diff --git a/internal/engine/ooapi/apis_test.go b/internal/ooapi/apis_test.go
similarity index 99%
rename from internal/engine/ooapi/apis_test.go
rename to internal/ooapi/apis_test.go
index 792df41..6171074 100644
--- a/internal/engine/ooapi/apis_test.go
+++ b/internal/ooapi/apis_test.go
@@ -18,7 +18,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func TestCheckReportIDInvalidURL(t *testing.T) {
diff --git a/internal/engine/ooapi/caching.go b/internal/ooapi/caching.go
similarity index 97%
rename from internal/engine/ooapi/caching.go
rename to internal/ooapi/caching.go
index e3171d5..640cdcc 100644
--- a/internal/engine/ooapi/caching.go
+++ b/internal/ooapi/caching.go
@@ -9,7 +9,7 @@ import (
 	"context"
 	"reflect"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 // withCacheMeasurementMetaAPI implements caching for simpleMeasurementMetaAPI.
diff --git a/internal/engine/ooapi/caching_test.go b/internal/ooapi/caching_test.go
similarity index 94%
rename from internal/engine/ooapi/caching_test.go
rename to internal/ooapi/caching_test.go
index 746df68..0c6c1c7 100644
--- a/internal/engine/ooapi/caching_test.go
+++ b/internal/ooapi/caching_test.go
@@ -11,7 +11,8 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func TestCachesimpleMeasurementMetaAPISuccess(t *testing.T) {
@@ -22,7 +23,7 @@ func TestCachesimpleMeasurementMetaAPISuccess(t *testing.T) {
 		API: &FakeMeasurementMetaAPI{
 			Response: expect,
 		},
-		KVStore: &MemKVStore{},
+		KVStore: &kvstore.Memory{},
 	}
 	var req *apimodel.MeasurementMetaRequest
 	ff.fill(&req)
@@ -69,7 +70,7 @@ func TestCachesimpleMeasurementMetaAPIFailureWithNoCache(t *testing.T) {
 		API: &FakeMeasurementMetaAPI{
 			Err: errMocked,
 		},
-		KVStore: &MemKVStore{},
+		KVStore: &kvstore.Memory{},
 	}
 	var req *apimodel.MeasurementMetaRequest
 	ff.fill(&req)
@@ -92,7 +93,7 @@ func TestCachesimpleMeasurementMetaAPIFailureWithPreviousCache(t *testing.T) {
 	}
 	cache := &withCacheMeasurementMetaAPI{
 		API:     fakeapi,
-		KVStore: &MemKVStore{},
+		KVStore: &kvstore.Memory{},
 	}
 	var req *apimodel.MeasurementMetaRequest
 	ff.fill(&req)
@@ -146,7 +147,7 @@ func TestCachesimpleMeasurementMetaAPIReadCacheNotFound(t *testing.T) {
 	var incache []cacheEntryForMeasurementMetaAPI
 	ff.fill(&incache)
 	cache := &withCacheMeasurementMetaAPI{
-		KVStore: &MemKVStore{},
+		KVStore: &kvstore.Memory{},
 	}
 	err := cache.setcache(incache)
 	if err != nil {
@@ -172,7 +173,7 @@ func TestCachesimpleMeasurementMetaAPIWriteCacheDuplicate(t *testing.T) {
 	var resp2 *apimodel.MeasurementMetaResponse
 	ff.fill(&resp2)
 	cache := &withCacheMeasurementMetaAPI{
-		KVStore: &MemKVStore{},
+		KVStore: &kvstore.Memory{},
 	}
 	err := cache.writecache(req, resp1)
 	if err != nil {
@@ -197,7 +198,7 @@ func TestCachesimpleMeasurementMetaAPIWriteCacheDuplicate(t *testing.T) {
 func TestCachesimpleMeasurementMetaAPICacheSizeLimited(t *testing.T) {
 	ff := &fakeFill{}
 	cache := &withCacheMeasurementMetaAPI{
-		KVStore: &MemKVStore{},
+		KVStore: &kvstore.Memory{},
 	}
 	var prev int
 	for {
diff --git a/internal/engine/ooapi/callers.go b/internal/ooapi/callers.go
similarity index 97%
rename from internal/engine/ooapi/callers.go
rename to internal/ooapi/callers.go
index 042addc..87a9fe8 100644
--- a/internal/engine/ooapi/callers.go
+++ b/internal/ooapi/callers.go
@@ -8,7 +8,7 @@ package ooapi
 import (
 	"context"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 // callerForCheckReportIDAPI represents any type exposing a method
diff --git a/internal/engine/ooapi/client.go b/internal/ooapi/client.go
similarity index 100%
rename from internal/engine/ooapi/client.go
rename to internal/ooapi/client.go
diff --git a/internal/engine/ooapi/clientcall.go b/internal/ooapi/clientcall.go
similarity index 98%
rename from internal/engine/ooapi/clientcall.go
rename to internal/ooapi/clientcall.go
index 2347207..6e094ea 100644
--- a/internal/engine/ooapi/clientcall.go
+++ b/internal/ooapi/clientcall.go
@@ -8,7 +8,7 @@ package ooapi
 import (
 	"context"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func (c *Client) newCheckReportIDCaller() callerForCheckReportIDAPI {
diff --git a/internal/engine/ooapi/clientcall_test.go b/internal/ooapi/clientcall_test.go
similarity index 96%
rename from internal/engine/ooapi/clientcall_test.go
rename to internal/ooapi/clientcall_test.go
index f52a087..438b655 100644
--- a/internal/engine/ooapi/clientcall_test.go
+++ b/internal/ooapi/clientcall_test.go
@@ -16,7 +16,8 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 type handleClientCallCheckReportID struct {
@@ -72,7 +73,7 @@ func TestCheckReportIDClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.CheckReportIDRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -165,7 +166,7 @@ func TestCheckInClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.CheckInRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -257,7 +258,7 @@ func TestMeasurementMetaClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.MeasurementMetaRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -350,7 +351,7 @@ func TestTestHelpersClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.TestHelpersRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -465,7 +466,7 @@ func TestPsiphonConfigClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.PsiphonConfigRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -580,7 +581,7 @@ func TestTorTargetsClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.TorTargetsRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -673,7 +674,7 @@ func TestURLsClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.URLsRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -766,7 +767,7 @@ func TestOpenReportClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.OpenReportRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
@@ -858,7 +859,7 @@ func TestSubmitMeasurementClientCallRoundTrip(t *testing.T) {
 	req := &apimodel.SubmitMeasurementRequest{}
 	ff := &fakeFill{}
 	ff.fill(&req)
-	clnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}
+	clnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}
 	ff.fill(&clnt.UserAgent)
 	// issue request
 	ctx := context.Background()
diff --git a/internal/engine/ooapi/cloners.go b/internal/ooapi/cloners.go
similarity index 100%
rename from internal/engine/ooapi/cloners.go
rename to internal/ooapi/cloners.go
diff --git a/internal/engine/ooapi/default.go b/internal/ooapi/default.go
similarity index 100%
rename from internal/engine/ooapi/default.go
rename to internal/ooapi/default.go
diff --git a/internal/engine/ooapi/default_test.go b/internal/ooapi/default_test.go
similarity index 100%
rename from internal/engine/ooapi/default_test.go
rename to internal/ooapi/default_test.go
diff --git a/internal/engine/ooapi/dependencies.go b/internal/ooapi/dependencies.go
similarity index 100%
rename from internal/engine/ooapi/dependencies.go
rename to internal/ooapi/dependencies.go
diff --git a/internal/engine/ooapi/doc.go b/internal/ooapi/doc.go
similarity index 100%
rename from internal/engine/ooapi/doc.go
rename to internal/ooapi/doc.go
diff --git a/internal/engine/ooapi/errors.go b/internal/ooapi/errors.go
similarity index 100%
rename from internal/engine/ooapi/errors.go
rename to internal/ooapi/errors.go
diff --git a/internal/engine/ooapi/fake_test.go b/internal/ooapi/fake_test.go
similarity index 100%
rename from internal/engine/ooapi/fake_test.go
rename to internal/ooapi/fake_test.go
diff --git a/internal/engine/ooapi/fakeapi_test.go b/internal/ooapi/fakeapi_test.go
similarity index 80%
rename from internal/engine/ooapi/fakeapi_test.go
rename to internal/ooapi/fakeapi_test.go
index cf617e3..12d2e14 100644
--- a/internal/engine/ooapi/fakeapi_test.go
+++ b/internal/ooapi/fakeapi_test.go
@@ -7,19 +7,21 @@ package ooapi
 
 import (
 	"context"
-	"sync/atomic"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 type FakeCheckReportIDAPI struct {
 	Err       error
 	Response  *apimodel.CheckReportIDResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeCheckReportIDAPI) Call(ctx context.Context, req *apimodel.CheckReportIDRequest) (*apimodel.CheckReportIDResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -30,11 +32,13 @@ var (
 type FakeCheckInAPI struct {
 	Err       error
 	Response  *apimodel.CheckInResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeCheckInAPI) Call(ctx context.Context, req *apimodel.CheckInRequest) (*apimodel.CheckInResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -45,11 +49,13 @@ var (
 type FakeLoginAPI struct {
 	Err       error
 	Response  *apimodel.LoginResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeLoginAPI) Call(ctx context.Context, req *apimodel.LoginRequest) (*apimodel.LoginResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -60,11 +66,13 @@ var (
 type FakeMeasurementMetaAPI struct {
 	Err       error
 	Response  *apimodel.MeasurementMetaResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeMeasurementMetaAPI) Call(ctx context.Context, req *apimodel.MeasurementMetaRequest) (*apimodel.MeasurementMetaResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -75,11 +83,13 @@ var (
 type FakeRegisterAPI struct {
 	Err       error
 	Response  *apimodel.RegisterResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeRegisterAPI) Call(ctx context.Context, req *apimodel.RegisterRequest) (*apimodel.RegisterResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -90,11 +100,13 @@ var (
 type FakeTestHelpersAPI struct {
 	Err       error
 	Response  apimodel.TestHelpersResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeTestHelpersAPI) Call(ctx context.Context, req *apimodel.TestHelpersRequest) (apimodel.TestHelpersResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -106,11 +118,13 @@ type FakePsiphonConfigAPI struct {
 	WithResult callerForPsiphonConfigAPI
 	Err        error
 	Response   apimodel.PsiphonConfigResponse
-	CountCall  int32
+	CountCall  *atomicx.Int64
 }
 
 func (fapi *FakePsiphonConfigAPI) Call(ctx context.Context, req *apimodel.PsiphonConfigRequest) (apimodel.PsiphonConfigResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -127,11 +141,13 @@ type FakeTorTargetsAPI struct {
 	WithResult callerForTorTargetsAPI
 	Err        error
 	Response   apimodel.TorTargetsResponse
-	CountCall  int32
+	CountCall  *atomicx.Int64
 }
 
 func (fapi *FakeTorTargetsAPI) Call(ctx context.Context, req *apimodel.TorTargetsRequest) (apimodel.TorTargetsResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -147,11 +163,13 @@ var (
 type FakeURLsAPI struct {
 	Err       error
 	Response  *apimodel.URLsResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeURLsAPI) Call(ctx context.Context, req *apimodel.URLsRequest) (*apimodel.URLsResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -162,11 +180,13 @@ var (
 type FakeOpenReportAPI struct {
 	Err       error
 	Response  *apimodel.OpenReportResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeOpenReportAPI) Call(ctx context.Context, req *apimodel.OpenReportRequest) (*apimodel.OpenReportResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
@@ -177,11 +197,13 @@ var (
 type FakeSubmitMeasurementAPI struct {
 	Err       error
 	Response  *apimodel.SubmitMeasurementResponse
-	CountCall int32
+	CountCall *atomicx.Int64
 }
 
 func (fapi *FakeSubmitMeasurementAPI) Call(ctx context.Context, req *apimodel.SubmitMeasurementRequest) (*apimodel.SubmitMeasurementResponse, error) {
-	atomic.AddInt32(&fapi.CountCall, 1)
+	if fapi.CountCall != nil {
+		fapi.CountCall.Add(1)
+	}
 	return fapi.Response, fapi.Err
 }
 
diff --git a/internal/engine/ooapi/fakefill_test.go b/internal/ooapi/fakefill_test.go
similarity index 98%
rename from internal/engine/ooapi/fakefill_test.go
rename to internal/ooapi/fakefill_test.go
index 5ee7776..32f1078 100644
--- a/internal/engine/ooapi/fakefill_test.go
+++ b/internal/ooapi/fakefill_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 // fakeFill fills specific data structures with random data. The only
diff --git a/internal/engine/ooapi/httpclient_test.go b/internal/ooapi/httpclient_test.go
similarity index 100%
rename from internal/engine/ooapi/httpclient_test.go
rename to internal/ooapi/httpclient_test.go
diff --git a/internal/engine/ooapi/integration_test.go b/internal/ooapi/integration_test.go
similarity index 85%
rename from internal/engine/ooapi/integration_test.go
rename to internal/ooapi/integration_test.go
index 59e0eea..3a7c1a0 100644
--- a/internal/engine/ooapi/integration_test.go
+++ b/internal/ooapi/integration_test.go
@@ -4,8 +4,9 @@ import (
 	"context"
 	"testing"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi"
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/ooapi"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func TestWithRealServerDoCheckIn(t *testing.T) {
@@ -26,7 +27,7 @@ func TestWithRealServerDoCheckIn(t *testing.T) {
 		},
 	}
 	httpClnt := &ooapi.VerboseHTTPClient{T: t}
-	clnt := &ooapi.Client{HTTPClient: httpClnt, KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{HTTPClient: httpClnt, KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.CheckIn(ctx, req)
 	if err != nil {
@@ -50,7 +51,7 @@ func TestWithRealServerDoCheckReportID(t *testing.T) {
 	req := &apimodel.CheckReportIDRequest{
 		ReportID: "20210223T093606Z_ndt_JO_8376_n1_kDYToqrugDY54Soy",
 	}
-	clnt := &ooapi.Client{KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.CheckReportID(ctx, req)
 	if err != nil {
@@ -69,7 +70,7 @@ func TestWithRealServerDoMeasurementMeta(t *testing.T) {
 	req := &apimodel.MeasurementMetaRequest{
 		ReportID: "20210223T093606Z_ndt_JO_8376_n1_kDYToqrugDY54Soy",
 	}
-	clnt := &ooapi.Client{KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.MeasurementMeta(ctx, req)
 	if err != nil {
@@ -96,7 +97,7 @@ func TestWithRealServerDoOpenReport(t *testing.T) {
 		TestStartTime:     "2018-11-01 15:33:20",
 		TestVersion:       "0.1.0",
 	}
-	clnt := &ooapi.Client{KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.OpenReport(ctx, req)
 	if err != nil {
@@ -114,7 +115,7 @@ func TestWithRealServerDoPsiphonConfig(t *testing.T) {
 	}
 	req := &apimodel.PsiphonConfigRequest{}
 	httpClnt := &ooapi.VerboseHTTPClient{T: t}
-	clnt := &ooapi.Client{HTTPClient: httpClnt, KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{HTTPClient: httpClnt, KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.PsiphonConfig(ctx, req)
 	if err != nil {
@@ -132,7 +133,7 @@ func TestWithRealServerDoTorTargets(t *testing.T) {
 	}
 	req := &apimodel.TorTargetsRequest{}
 	httpClnt := &ooapi.VerboseHTTPClient{T: t}
-	clnt := &ooapi.Client{HTTPClient: httpClnt, KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{HTTPClient: httpClnt, KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.TorTargets(ctx, req)
 	if err != nil {
@@ -152,7 +153,7 @@ func TestWithRealServerDoURLs(t *testing.T) {
 		CountryCode: "IT",
 		Limit:       3,
 	}
-	clnt := &ooapi.Client{KVStore: &ooapi.MemKVStore{}}
+	clnt := &ooapi.Client{KVStore: &kvstore.Memory{}}
 	ctx := context.Background()
 	resp, err := clnt.URLs(ctx, req)
 	if err != nil {
diff --git a/internal/engine/ooapi/internal/generator/apis.go b/internal/ooapi/internal/generator/apis.go
similarity index 98%
rename from internal/engine/ooapi/internal/generator/apis.go
rename to internal/ooapi/internal/generator/apis.go
index 56536db..1d15cda 100644
--- a/internal/engine/ooapi/internal/generator/apis.go
+++ b/internal/ooapi/internal/generator/apis.go
@@ -171,7 +171,7 @@ func GenAPIsGo(file string) {
 	fmt.Fprint(&sb, "\t\"context\"\n")
 	fmt.Fprint(&sb, "\t\"net/http\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		desc.genNewAPI(&sb)
diff --git a/internal/engine/ooapi/internal/generator/apistest.go b/internal/ooapi/internal/generator/apistest.go
similarity index 99%
rename from internal/engine/ooapi/internal/generator/apistest.go
rename to internal/ooapi/internal/generator/apistest.go
index 31cacbe..feeb7c8 100644
--- a/internal/engine/ooapi/internal/generator/apistest.go
+++ b/internal/ooapi/internal/generator/apistest.go
@@ -452,7 +452,7 @@ func GenAPIsTestGo(file string) {
 	fmt.Fprint(&sb, "\t\"sync\"\n")
 	fmt.Fprint(&sb, "\n")
 	fmt.Fprint(&sb, "\t\"github.com/google/go-cmp/cmp\"\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		desc.genAPITests(&sb)
diff --git a/internal/engine/ooapi/internal/generator/caching.go b/internal/ooapi/internal/generator/caching.go
similarity index 98%
rename from internal/engine/ooapi/internal/generator/caching.go
rename to internal/ooapi/internal/generator/caching.go
index 75a2bc9..1ceff42 100644
--- a/internal/engine/ooapi/internal/generator/caching.go
+++ b/internal/ooapi/internal/generator/caching.go
@@ -118,7 +118,7 @@ func GenCachingGo(file string) {
 	fmt.Fprint(&sb, "\t\"context\"\n")
 	fmt.Fprint(&sb, "\t\"reflect\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		if desc.CachePolicy == CacheNone {
diff --git a/internal/engine/ooapi/internal/generator/cachingtest.go b/internal/ooapi/internal/generator/cachingtest.go
similarity index 95%
rename from internal/engine/ooapi/internal/generator/cachingtest.go
rename to internal/ooapi/internal/generator/cachingtest.go
index c56459d..02c0ec9 100644
--- a/internal/engine/ooapi/internal/generator/cachingtest.go
+++ b/internal/ooapi/internal/generator/cachingtest.go
@@ -15,7 +15,7 @@ func (d *Descriptor) genTestCacheSuccess(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\t\tAPI: &%s{\n", d.FakeAPIStructName())
 	fmt.Fprint(sb, "\t\t\tResponse: expect,\n")
 	fmt.Fprint(sb, "\t\t},\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
 	fmt.Fprint(sb, "\tff.fill(&req)\n")
@@ -66,7 +66,7 @@ func (d *Descriptor) genTestFailureWithNoCache(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\t\tAPI: &%s{\n", d.FakeAPIStructName())
 	fmt.Fprint(sb, "\t\t\tErr: errMocked,\n")
 	fmt.Fprint(sb, "\t\t},\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
 	fmt.Fprint(sb, "\tff.fill(&req)\n")
@@ -92,7 +92,7 @@ func (d *Descriptor) genTestFailureWithPreviousCache(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\tcache := &%s{\n", d.WithCacheAPIStructName())
 	fmt.Fprint(sb, "\t\tAPI: fakeapi,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
 	fmt.Fprint(sb, "\tff.fill(&req)\n")
@@ -156,7 +156,7 @@ func (d *Descriptor) genTestReadCacheNotFound(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\tvar incache []%s\n", d.CacheEntryName())
 	fmt.Fprint(sb, "\tff.fill(&incache)\n")
 	fmt.Fprintf(sb, "\tcache := &%s{\n", d.WithCacheAPIStructName())
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\terr := cache.setcache(incache)\n")
 	fmt.Fprintf(sb, "\tif err != nil {\n")
@@ -184,7 +184,7 @@ func (d *Descriptor) genTestWriteCacheDuplicate(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\tvar resp2 %s\n", d.ResponseTypeName())
 	fmt.Fprint(sb, "\tff.fill(&resp2)\n")
 	fmt.Fprintf(sb, "\tcache := &%s{\n", d.WithCacheAPIStructName())
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\terr := cache.writecache(req, resp1)\n")
 	fmt.Fprintf(sb, "\tif err != nil {\n")
@@ -217,7 +217,7 @@ func (d *Descriptor) genTestCachSizeLimited(sb *strings.Builder) {
 	fmt.Fprintf(sb, "func TestCache%sCacheSizeLimited(t *testing.T) {\n", d.APIStructName())
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
 	fmt.Fprintf(sb, "\tcache := &%s{\n", d.WithCacheAPIStructName())
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprintf(sb, "\tvar prev int\n")
 	fmt.Fprintf(sb, "\tfor {\n")
@@ -255,7 +255,8 @@ func GenCachingTestGo(file string) {
 	fmt.Fprint(&sb, "\t\"testing\"\n")
 	fmt.Fprint(&sb, "\n")
 	fmt.Fprint(&sb, "\t\"github.com/google/go-cmp/cmp\"\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/kvstore\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		if desc.CachePolicy == CacheNone {
diff --git a/internal/engine/ooapi/internal/generator/callers.go b/internal/ooapi/internal/generator/callers.go
similarity index 91%
rename from internal/engine/ooapi/internal/generator/callers.go
rename to internal/ooapi/internal/generator/callers.go
index 4ba8ea8..1ce873b 100644
--- a/internal/engine/ooapi/internal/generator/callers.go
+++ b/internal/ooapi/internal/generator/callers.go
@@ -26,7 +26,7 @@ func GenCallersGo(file string) {
 	fmt.Fprint(&sb, "import (\n")
 	fmt.Fprint(&sb, "\t\"context\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		desc.genNewCaller(&sb)
diff --git a/internal/engine/ooapi/internal/generator/clientcall.go b/internal/ooapi/internal/generator/clientcall.go
similarity index 97%
rename from internal/engine/ooapi/internal/generator/clientcall.go
rename to internal/ooapi/internal/generator/clientcall.go
index eeb688d..3b36063 100644
--- a/internal/engine/ooapi/internal/generator/clientcall.go
+++ b/internal/ooapi/internal/generator/clientcall.go
@@ -89,7 +89,7 @@ func GenClientCallGo(file string) {
 	fmt.Fprint(&sb, "import (\n")
 	fmt.Fprint(&sb, "\t\"context\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		switch desc.Name {
diff --git a/internal/engine/ooapi/internal/generator/clientcalltest.go b/internal/ooapi/internal/generator/clientcalltest.go
similarity index 96%
rename from internal/engine/ooapi/internal/generator/clientcalltest.go
rename to internal/ooapi/internal/generator/clientcalltest.go
index f840eff..0443d80 100644
--- a/internal/engine/ooapi/internal/generator/clientcalltest.go
+++ b/internal/ooapi/internal/generator/clientcalltest.go
@@ -90,7 +90,7 @@ func (d *Descriptor) genTestClientCallRoundTrip(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\treq := &%s{}\n", d.RequestTypeNameAsStruct())
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
 	fmt.Fprint(sb, "\tff.fill(&req)\n")
-	fmt.Fprint(sb, "\tclnt := &Client{KVStore: &MemKVStore{}, BaseURL: srvr.URL}\n")
+	fmt.Fprint(sb, "\tclnt := &Client{KVStore: &kvstore.Memory{}, BaseURL: srvr.URL}\n")
 	fmt.Fprint(sb, "\tff.fill(&clnt.UserAgent)\n")
 
 	fmt.Fprint(sb, "\t// issue request\n")
@@ -169,7 +169,8 @@ func GenClientCallTestGo(file string) {
 	fmt.Fprint(&sb, "\t\"sync\"\n")
 	fmt.Fprint(&sb, "\n")
 	fmt.Fprint(&sb, "\t\"github.com/google/go-cmp/cmp\"\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/kvstore\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		if desc.Name == "Login" || desc.Name == "Register" {
diff --git a/internal/engine/ooapi/internal/generator/cloners.go b/internal/ooapi/internal/generator/cloners.go
similarity index 100%
rename from internal/engine/ooapi/internal/generator/cloners.go
rename to internal/ooapi/internal/generator/cloners.go
diff --git a/internal/engine/ooapi/internal/generator/fakeapitest.go b/internal/ooapi/internal/generator/fakeapitest.go
similarity index 83%
rename from internal/engine/ooapi/internal/generator/fakeapitest.go
rename to internal/ooapi/internal/generator/fakeapitest.go
index 48b12c2..fa40441 100644
--- a/internal/engine/ooapi/internal/generator/fakeapitest.go
+++ b/internal/ooapi/internal/generator/fakeapitest.go
@@ -13,12 +13,14 @@ func (d *Descriptor) genNewFakeAPI(sb *strings.Builder) {
 	}
 	fmt.Fprint(sb, "\tErr error\n")
 	fmt.Fprintf(sb, "\tResponse %s\n", d.ResponseTypeName())
-	fmt.Fprint(sb, "\tCountCall int32\n")
+	fmt.Fprint(sb, "\tCountCall *atomicx.Int64\n")
 	fmt.Fprint(sb, "}\n\n")
 
 	fmt.Fprintf(sb, "func (fapi *%s) Call(ctx context.Context, req %s) (%s, error) {\n",
 		d.FakeAPIStructName(), d.RequestTypeName(), d.ResponseTypeName())
-	fmt.Fprint(sb, "\tatomic.AddInt32(&fapi.CountCall, 1)\n")
+	fmt.Fprint(sb, "\tif fapi.CountCall != nil {\n")
+	fmt.Fprint(sb, "\t\tfapi.CountCall.Add(1)\n")
+	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprint(sb, "\treturn fapi.Response, fapi.Err\n")
 	fmt.Fprint(sb, "}\n\n")
 
@@ -48,9 +50,9 @@ func GenFakeAPITestGo(file string) {
 	fmt.Fprintf(&sb, "//go:generate go run ./internal/generator -file %s\n\n", file)
 	fmt.Fprint(&sb, "import (\n")
 	fmt.Fprint(&sb, "\t\"context\"\n")
-	fmt.Fprint(&sb, "\t\"sync/atomic\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/atomicx\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		desc.genNewFakeAPI(&sb)
diff --git a/internal/engine/ooapi/internal/generator/generator.go b/internal/ooapi/internal/generator/generator.go
similarity index 100%
rename from internal/engine/ooapi/internal/generator/generator.go
rename to internal/ooapi/internal/generator/generator.go
diff --git a/internal/engine/ooapi/internal/generator/login.go b/internal/ooapi/internal/generator/login.go
similarity index 98%
rename from internal/engine/ooapi/internal/generator/login.go
rename to internal/ooapi/internal/generator/login.go
index 61dedba..c58ee3d 100644
--- a/internal/engine/ooapi/internal/generator/login.go
+++ b/internal/ooapi/internal/generator/login.go
@@ -170,7 +170,7 @@ func GenLoginGo(file string) {
 	fmt.Fprint(&sb, "\t\"context\"\n")
 	fmt.Fprint(&sb, "\t\"errors\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		if !desc.RequiresLogin {
diff --git a/internal/engine/ooapi/internal/generator/logintest.go b/internal/ooapi/internal/generator/logintest.go
similarity index 86%
rename from internal/engine/ooapi/internal/generator/logintest.go
rename to internal/ooapi/internal/generator/logintest.go
index 7960f3c..58122a6 100644
--- a/internal/engine/ooapi/internal/generator/logintest.go
+++ b/internal/ooapi/internal/generator/logintest.go
@@ -16,6 +16,7 @@ func (d *Descriptor) genTestRegisterAndLoginSuccess(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tResponse: &apimodel.RegisterResponse{\n")
 	fmt.Fprint(sb, "\t\t\tClientID: \"antani-antani\",\n")
 	fmt.Fprint(sb, "\t\t},\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprint(sb, "\t\tloginAPI := &FakeLoginAPI{\n")
@@ -23,6 +24,7 @@ func (d *Descriptor) genTestRegisterAndLoginSuccess(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\t\tExpire: time.Now().Add(3600*time.Second),\n")
 	fmt.Fprint(sb, "\t\t\t\tToken: \"antani-antani-token\",\n")
 	fmt.Fprint(sb, "\t\t\t},\n")
+	fmt.Fprint(sb, "\t\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
 	fmt.Fprintf(sb, "\tlogin := &%s{\n", d.WithLoginAPIStructName())
@@ -33,7 +35,7 @@ func (d *Descriptor) genTestRegisterAndLoginSuccess(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\t\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -50,11 +52,11 @@ func (d *Descriptor) genTestRegisterAndLoginSuccess(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(diff)\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -71,6 +73,7 @@ func (d *Descriptor) genTestContinueUsingToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tResponse: &apimodel.RegisterResponse{\n")
 	fmt.Fprint(sb, "\t\t\tClientID: \"antani-antani\",\n")
 	fmt.Fprint(sb, "\t\t},\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprint(sb, "\t\tloginAPI := &FakeLoginAPI{\n")
@@ -78,6 +81,7 @@ func (d *Descriptor) genTestContinueUsingToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\t\tExpire: time.Now().Add(3600*time.Second),\n")
 	fmt.Fprint(sb, "\t\t\t\tToken: \"antani-antani-token\",\n")
 	fmt.Fprint(sb, "\t\t\t},\n")
+	fmt.Fprint(sb, "\t\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
 	fmt.Fprintf(sb, "\tlogin := &%s{\n", d.WithLoginAPIStructName())
@@ -88,7 +92,7 @@ func (d *Descriptor) genTestContinueUsingToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\t\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -110,11 +114,11 @@ func (d *Descriptor) genTestContinueUsingToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\tt.Fatal(diff)\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\t\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\t\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 	fmt.Fprint(sb, "\t}\n")
@@ -138,11 +142,11 @@ func (d *Descriptor) genTestContinueUsingToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(diff)\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -158,6 +162,7 @@ func (d *Descriptor) genTestWithValidButExpiredToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\terrMocked := errors.New(\"mocked error\")\n")
 	fmt.Fprint(sb, "\tregisterAPI := &FakeRegisterAPI{\n")
 	fmt.Fprint(sb, "\t\tErr: errMocked,\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprint(sb, "\t\tloginAPI := &FakeLoginAPI{\n")
@@ -165,6 +170,7 @@ func (d *Descriptor) genTestWithValidButExpiredToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\t\tExpire: time.Now().Add(3600*time.Second),\n")
 	fmt.Fprint(sb, "\t\t\t\tToken: \"antani-antani-token\",\n")
 	fmt.Fprint(sb, "\t\t\t},\n")
+	fmt.Fprint(sb, "\t\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
 	fmt.Fprintf(sb, "\tlogin := &%s{\n", d.WithLoginAPIStructName())
@@ -175,7 +181,7 @@ func (d *Descriptor) genTestWithValidButExpiredToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\t\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tls := &loginState{\n")
@@ -202,11 +208,11 @@ func (d *Descriptor) genTestWithValidButExpiredToken(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(diff)\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 0 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 0 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -222,6 +228,7 @@ func (d *Descriptor) genTestWithRegisterAPIError(sb *strings.Builder) {
 	fmt.Fprint(sb, "\terrMocked := errors.New(\"mocked error\")\n")
 	fmt.Fprint(sb, "\tregisterAPI := &FakeRegisterAPI{\n")
 	fmt.Fprint(sb, "\t\tErr: errMocked,\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tlogin := &%s{\n", d.WithLoginAPIStructName())
@@ -231,7 +238,7 @@ func (d *Descriptor) genTestWithRegisterAPIError(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\t},\n")
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -245,7 +252,7 @@ func (d *Descriptor) genTestWithRegisterAPIError(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -262,11 +269,13 @@ func (d *Descriptor) genTestWithLoginFailure(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tResponse: &apimodel.RegisterResponse{\n")
 	fmt.Fprint(sb, "\t\t\tClientID: \"antani-antani\",\n")
 	fmt.Fprint(sb, "\t\t},\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprint(sb, "\terrMocked := errors.New(\"mocked error\")\n")
 	fmt.Fprint(sb, "\t\tloginAPI := &FakeLoginAPI{\n")
 	fmt.Fprint(sb, "\t\t\tErr: errMocked,\n")
+	fmt.Fprint(sb, "\t\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
 	fmt.Fprintf(sb, "\tlogin := &%s{\n", d.WithLoginAPIStructName())
@@ -277,7 +286,7 @@ func (d *Descriptor) genTestWithLoginFailure(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\t\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -291,11 +300,11 @@ func (d *Descriptor) genTestWithLoginFailure(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -312,6 +321,7 @@ func (d *Descriptor) genTestRegisterAndLoginThenFail(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tResponse: &apimodel.RegisterResponse{\n")
 	fmt.Fprint(sb, "\t\t\tClientID: \"antani-antani\",\n")
 	fmt.Fprint(sb, "\t\t},\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprint(sb, "\t\tloginAPI := &FakeLoginAPI{\n")
@@ -319,6 +329,7 @@ func (d *Descriptor) genTestRegisterAndLoginThenFail(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\t\tExpire: time.Now().Add(3600*time.Second),\n")
 	fmt.Fprint(sb, "\t\t\t\tToken: \"antani-antani-token\",\n")
 	fmt.Fprint(sb, "\t\t\t},\n")
+	fmt.Fprint(sb, "\t\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
 	fmt.Fprint(sb, "\terrMocked := errors.New(\"mocked error\")\n")
@@ -330,7 +341,7 @@ func (d *Descriptor) genTestRegisterAndLoginThenFail(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\t\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -344,11 +355,11 @@ func (d *Descriptor) genTestRegisterAndLoginThenFail(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -358,7 +369,11 @@ func (d *Descriptor) genTestRegisterAndLoginThenFail(sb *strings.Builder) {
 func (d *Descriptor) genTestTheDatabaseIsReplaced(sb *strings.Builder) {
 	fmt.Fprintf(sb, "func Test%sTheDatabaseIsReplaced(t *testing.T) {\n", d.Name)
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
-	fmt.Fprint(sb, "\thandler := &LoginHandler{t: t}\n")
+	fmt.Fprint(sb, "\thandler := &LoginHandler{\n")
+	fmt.Fprint(sb, "\t\tlogins: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tregisters: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tt: t,\n")
+	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprint(sb, "\tsrvr := httptest.NewServer(handler)\n")
 	fmt.Fprint(sb, "\tdefer srvr.Close()\n")
 
@@ -379,7 +394,7 @@ func (d *Descriptor) genTestTheDatabaseIsReplaced(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\tAPI : baseAPI,\n")
 	fmt.Fprint(sb, "\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -398,11 +413,11 @@ func (d *Descriptor) genTestTheDatabaseIsReplaced(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.logins != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.logins.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 	fmt.Fprint(sb, "\t}\n")
@@ -418,11 +433,11 @@ func (d *Descriptor) genTestTheDatabaseIsReplaced(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.logins != 3 {\n")
+	fmt.Fprint(sb, "\tif handler.logins.Load() != 3 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.registers != 2 {\n")
+	fmt.Fprint(sb, "\tif handler.registers.Load() != 2 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -432,7 +447,11 @@ func (d *Descriptor) genTestTheDatabaseIsReplaced(sb *strings.Builder) {
 func (d *Descriptor) genTestTheDatabaseIsReplacedThenFailure(sb *strings.Builder) {
 	fmt.Fprintf(sb, "func Test%sTheDatabaseIsReplacedThenFailure(t *testing.T) {\n", d.Name)
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
-	fmt.Fprint(sb, "\thandler := &LoginHandler{t: t}\n")
+	fmt.Fprint(sb, "\thandler := &LoginHandler{\n")
+	fmt.Fprint(sb, "\t\tlogins: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tregisters: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tt: t,\n")
+	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprint(sb, "\tsrvr := httptest.NewServer(handler)\n")
 	fmt.Fprint(sb, "\tdefer srvr.Close()\n")
 
@@ -453,7 +472,7 @@ func (d *Descriptor) genTestTheDatabaseIsReplacedThenFailure(sb *strings.Builder
 	fmt.Fprintf(sb, "\tAPI : baseAPI,\n")
 	fmt.Fprint(sb, "\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -472,11 +491,11 @@ func (d *Descriptor) genTestTheDatabaseIsReplacedThenFailure(sb *strings.Builder
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.logins != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.logins.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 	fmt.Fprint(sb, "\t}\n")
@@ -494,11 +513,11 @@ func (d *Descriptor) genTestTheDatabaseIsReplacedThenFailure(sb *strings.Builder
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.logins != 2 {\n")
+	fmt.Fprint(sb, "\tif handler.logins.Load() != 2 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.registers != 2 {\n")
+	fmt.Fprint(sb, "\tif handler.registers.Load() != 2 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -515,6 +534,7 @@ func (d *Descriptor) genTestRegisterAndLoginCannotWriteState(sb *strings.Builder
 	fmt.Fprint(sb, "\t\tResponse: &apimodel.RegisterResponse{\n")
 	fmt.Fprint(sb, "\t\t\tClientID: \"antani-antani\",\n")
 	fmt.Fprint(sb, "\t\t},\n")
+	fmt.Fprint(sb, "\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprint(sb, "\t\tloginAPI := &FakeLoginAPI{\n")
@@ -522,6 +542,7 @@ func (d *Descriptor) genTestRegisterAndLoginCannotWriteState(sb *strings.Builder
 	fmt.Fprint(sb, "\t\t\t\tExpire: time.Now().Add(3600*time.Second),\n")
 	fmt.Fprint(sb, "\t\t\t\tToken: \"antani-antani-token\",\n")
 	fmt.Fprint(sb, "\t\t\t},\n")
+	fmt.Fprint(sb, "\t\t\tCountCall: &atomicx.Int64{},\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
 	fmt.Fprint(sb, "\terrMocked := errors.New(\"mocked error\")\n")
@@ -533,7 +554,7 @@ func (d *Descriptor) genTestRegisterAndLoginCannotWriteState(sb *strings.Builder
 	fmt.Fprint(sb, "\t\t},\n")
 	fmt.Fprint(sb, "\t\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\t\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t\tJSONCodec: &FakeCodec{\n")
 	fmt.Fprint(sb, "\t\t\tEncodeErr: errMocked,\n")
 	fmt.Fprint(sb, "\t\t},\n")
@@ -550,11 +571,11 @@ func (d *Descriptor) genTestRegisterAndLoginCannotWriteState(sb *strings.Builder
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif loginAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif loginAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid loginAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif registerAPI.CountCall != 1 {\n")
+	fmt.Fprint(sb, "\tif registerAPI.CountCall.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid registerAPI.CountCall\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -570,7 +591,7 @@ func (d *Descriptor) genTestReadStateDecodeFailure(sb *strings.Builder) {
 	fmt.Fprint(sb, "\terrMocked := errors.New(\"mocked error\")\n")
 
 	fmt.Fprintf(sb, "\tlogin := &%s{\n", d.WithLoginAPIStructName())
-	fmt.Fprint(sb, "\t\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\t\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t\tJSONCodec: &FakeCodec{DecodeErr: errMocked},\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -598,7 +619,11 @@ func (d *Descriptor) genTestReadStateDecodeFailure(sb *strings.Builder) {
 func (d *Descriptor) genTestClockIsOffThenSuccess(sb *strings.Builder) {
 	fmt.Fprintf(sb, "func Test%sClockIsOffThenSuccess(t *testing.T) {\n", d.Name)
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
-	fmt.Fprint(sb, "\thandler := &LoginHandler{t: t}\n")
+	fmt.Fprint(sb, "\thandler := &LoginHandler{\n")
+	fmt.Fprint(sb, "\t\tlogins: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tregisters: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tt: t,\n")
+	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprint(sb, "\tsrvr := httptest.NewServer(handler)\n")
 	fmt.Fprint(sb, "\tdefer srvr.Close()\n")
 
@@ -619,7 +644,7 @@ func (d *Descriptor) genTestClockIsOffThenSuccess(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\tAPI : baseAPI,\n")
 	fmt.Fprint(sb, "\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -638,11 +663,11 @@ func (d *Descriptor) genTestClockIsOffThenSuccess(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.logins != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.logins.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 	fmt.Fprint(sb, "\t}\n")
@@ -660,11 +685,11 @@ func (d *Descriptor) genTestClockIsOffThenSuccess(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.logins != 2 {\n")
+	fmt.Fprint(sb, "\tif handler.logins.Load() != 2 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -674,7 +699,11 @@ func (d *Descriptor) genTestClockIsOffThenSuccess(sb *strings.Builder) {
 func (d *Descriptor) genTestClockIsOffThen401(sb *strings.Builder) {
 	fmt.Fprintf(sb, "func Test%sClockIsOffThen401(t *testing.T) {\n", d.Name)
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
-	fmt.Fprint(sb, "\thandler := &LoginHandler{t: t}\n")
+	fmt.Fprint(sb, "\thandler := &LoginHandler{\n")
+	fmt.Fprint(sb, "\t\tlogins: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tregisters: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tt: t,\n")
+	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprint(sb, "\tsrvr := httptest.NewServer(handler)\n")
 	fmt.Fprint(sb, "\tdefer srvr.Close()\n")
 
@@ -695,7 +724,7 @@ func (d *Descriptor) genTestClockIsOffThen401(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\tAPI : baseAPI,\n")
 	fmt.Fprint(sb, "\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -714,11 +743,11 @@ func (d *Descriptor) genTestClockIsOffThen401(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.logins != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.logins.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 	fmt.Fprint(sb, "\t}\n")
@@ -737,11 +766,11 @@ func (d *Descriptor) genTestClockIsOffThen401(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.logins != 3 {\n")
+	fmt.Fprint(sb, "\tif handler.logins.Load() != 3 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.registers != 2 {\n")
+	fmt.Fprint(sb, "\tif handler.registers.Load() != 2 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -751,7 +780,11 @@ func (d *Descriptor) genTestClockIsOffThen401(sb *strings.Builder) {
 func (d *Descriptor) genTestClockIsOffThen500(sb *strings.Builder) {
 	fmt.Fprintf(sb, "func Test%sClockIsOffThen500(t *testing.T) {\n", d.Name)
 	fmt.Fprint(sb, "\tff := &fakeFill{}\n")
-	fmt.Fprint(sb, "\thandler := &LoginHandler{t: t}\n")
+	fmt.Fprint(sb, "\thandler := &LoginHandler{\n")
+	fmt.Fprint(sb, "\t\tlogins: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tregisters: &atomicx.Int64{},\n")
+	fmt.Fprint(sb, "\t\tt: t,\n")
+	fmt.Fprint(sb, "\t}\n")
 	fmt.Fprint(sb, "\tsrvr := httptest.NewServer(handler)\n")
 	fmt.Fprint(sb, "\tdefer srvr.Close()\n")
 
@@ -772,7 +805,7 @@ func (d *Descriptor) genTestClockIsOffThen500(sb *strings.Builder) {
 	fmt.Fprintf(sb, "\tAPI : baseAPI,\n")
 	fmt.Fprint(sb, "\tRegisterAPI: registerAPI,\n")
 	fmt.Fprint(sb, "\tLoginAPI: loginAPI,\n")
-	fmt.Fprint(sb, "\tKVStore: &MemKVStore{},\n")
+	fmt.Fprint(sb, "\tKVStore: &kvstore.Memory{},\n")
 	fmt.Fprint(sb, "\t}\n")
 
 	fmt.Fprintf(sb, "\tvar req %s\n", d.RequestTypeName())
@@ -791,11 +824,11 @@ func (d *Descriptor) genTestClockIsOffThen500(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"expected non-nil response\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.logins != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.logins.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 
-	fmt.Fprint(sb, "\t\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\t\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t\t}\n")
 	fmt.Fprint(sb, "\t}\n")
@@ -814,11 +847,11 @@ func (d *Descriptor) genTestClockIsOffThen500(sb *strings.Builder) {
 	fmt.Fprint(sb, "\t\tt.Fatal(\"expected nil response\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.logins != 2 {\n")
+	fmt.Fprint(sb, "\tif handler.logins.Load() != 2 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.logins\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
-	fmt.Fprint(sb, "\tif handler.registers != 1 {\n")
+	fmt.Fprint(sb, "\tif handler.registers.Load() != 1 {\n")
 	fmt.Fprint(sb, "\t\tt.Fatal(\"invalid handler.registers\")\n")
 	fmt.Fprint(sb, "\t}\n")
 
@@ -840,7 +873,9 @@ func GenLoginTestGo(file string) {
 	fmt.Fprint(&sb, "\t\"time\"\n")
 	fmt.Fprint(&sb, "\n")
 	fmt.Fprint(&sb, "\t\"github.com/google/go-cmp/cmp\"\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/atomicx\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/kvstore\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n")
 	for _, desc := range Descriptors {
 		if !desc.RequiresLogin {
diff --git a/internal/engine/ooapi/internal/generator/reflect.go b/internal/ooapi/internal/generator/reflect.go
similarity index 100%
rename from internal/engine/ooapi/internal/generator/reflect.go
rename to internal/ooapi/internal/generator/reflect.go
diff --git a/internal/engine/ooapi/internal/generator/requests.go b/internal/ooapi/internal/generator/requests.go
similarity index 97%
rename from internal/engine/ooapi/internal/generator/requests.go
rename to internal/ooapi/internal/generator/requests.go
index 1e02fa2..2041e21 100644
--- a/internal/engine/ooapi/internal/generator/requests.go
+++ b/internal/ooapi/internal/generator/requests.go
@@ -132,7 +132,7 @@ func GenRequestsGo(file string) {
 	fmt.Fprint(&sb, "\t\"net/http\"\n")
 	fmt.Fprint(&sb, "\t\"net/url\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n\n")
 	for _, desc := range Descriptors {
 		desc.genNewRequest(&sb)
diff --git a/internal/engine/ooapi/internal/generator/responses.go b/internal/ooapi/internal/generator/responses.go
similarity index 96%
rename from internal/engine/ooapi/internal/generator/responses.go
rename to internal/ooapi/internal/generator/responses.go
index 18ce9e2..da81013 100644
--- a/internal/engine/ooapi/internal/generator/responses.go
+++ b/internal/ooapi/internal/generator/responses.go
@@ -71,7 +71,7 @@ func GenResponsesGo(file string) {
 	fmt.Fprint(&sb, "\t\"io/ioutil\"\n")
 	fmt.Fprint(&sb, "\t\"net/http\"\n")
 	fmt.Fprint(&sb, "\n")
-	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel\"\n")
 	fmt.Fprint(&sb, ")\n\n")
 	for _, desc := range Descriptors {
 		desc.genNewResponse(&sb)
diff --git a/internal/engine/ooapi/internal/generator/spec.go b/internal/ooapi/internal/generator/spec.go
similarity index 98%
rename from internal/engine/ooapi/internal/generator/spec.go
rename to internal/ooapi/internal/generator/spec.go
index 01bd0c8..a8a6cde 100644
--- a/internal/engine/ooapi/internal/generator/spec.go
+++ b/internal/ooapi/internal/generator/spec.go
@@ -1,6 +1,6 @@
 package main
 
-import "github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+import "github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 
 // URLPath describes a URLPath.
 type URLPath struct {
diff --git a/internal/engine/ooapi/internal/generator/swaggertest.go b/internal/ooapi/internal/generator/swaggertest.go
similarity index 98%
rename from internal/engine/ooapi/internal/generator/swaggertest.go
rename to internal/ooapi/internal/generator/swaggertest.go
index 3fadc38..96ed826 100644
--- a/internal/engine/ooapi/internal/generator/swaggertest.go
+++ b/internal/ooapi/internal/generator/swaggertest.go
@@ -9,7 +9,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/internal/openapi"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/internal/openapi"
 )
 
 const (
diff --git a/internal/engine/ooapi/internal/generator/writefile.go b/internal/ooapi/internal/generator/writefile.go
similarity index 100%
rename from internal/engine/ooapi/internal/generator/writefile.go
rename to internal/ooapi/internal/generator/writefile.go
diff --git a/internal/engine/ooapi/internal/openapi/openapi.go b/internal/ooapi/internal/openapi/openapi.go
similarity index 100%
rename from internal/engine/ooapi/internal/openapi/openapi.go
rename to internal/ooapi/internal/openapi/openapi.go
diff --git a/internal/engine/ooapi/login.go b/internal/ooapi/login.go
similarity index 99%
rename from internal/engine/ooapi/login.go
rename to internal/ooapi/login.go
index 5c8f2b4..2c52aca 100644
--- a/internal/engine/ooapi/login.go
+++ b/internal/ooapi/login.go
@@ -9,7 +9,7 @@ import (
 	"context"
 	"errors"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 // withLoginPsiphonConfigAPI implements login for simplePsiphonConfigAPI.
diff --git a/internal/engine/ooapi/login_test.go b/internal/ooapi/login_test.go
similarity index 84%
rename from internal/engine/ooapi/login_test.go
rename to internal/ooapi/login_test.go
index a6e7624..8131618 100644
--- a/internal/engine/ooapi/login_test.go
+++ b/internal/ooapi/login_test.go
@@ -13,7 +13,9 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func TestRegisterAndLoginPsiphonConfigSuccess(t *testing.T) {
@@ -24,12 +26,14 @@ func TestRegisterAndLoginPsiphonConfigSuccess(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginPsiphonConfigAPI{
 		API: &FakePsiphonConfigAPI{
@@ -39,7 +43,7 @@ func TestRegisterAndLoginPsiphonConfigSuccess(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -54,10 +58,10 @@ func TestRegisterAndLoginPsiphonConfigSuccess(t *testing.T) {
 	if diff := cmp.Diff(expect, resp); diff != "" {
 		t.Fatal(diff)
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -70,12 +74,14 @@ func TestPsiphonConfigContinueUsingToken(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginPsiphonConfigAPI{
 		API: &FakePsiphonConfigAPI{
@@ -85,7 +91,7 @@ func TestPsiphonConfigContinueUsingToken(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -103,10 +109,10 @@ func TestPsiphonConfigContinueUsingToken(t *testing.T) {
 		if diff := cmp.Diff(expect, resp); diff != "" {
 			t.Fatal(diff)
 		}
-		if loginAPI.CountCall != 1 {
+		if loginAPI.CountCall.Load() != 1 {
 			t.Fatal("invalid loginAPI.CountCall")
 		}
-		if registerAPI.CountCall != 1 {
+		if registerAPI.CountCall.Load() != 1 {
 			t.Fatal("invalid registerAPI.CountCall")
 		}
 	}
@@ -127,10 +133,10 @@ func TestPsiphonConfigContinueUsingToken(t *testing.T) {
 	if diff := cmp.Diff(expect, resp); diff != "" {
 		t.Fatal(diff)
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -141,13 +147,15 @@ func TestPsiphonConfigWithValidButExpiredToken(t *testing.T) {
 	ff.fill(&expect)
 	errMocked := errors.New("mocked error")
 	registerAPI := &FakeRegisterAPI{
-		Err: errMocked,
+		Err:       errMocked,
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginPsiphonConfigAPI{
 		API: &FakePsiphonConfigAPI{
@@ -157,7 +165,7 @@ func TestPsiphonConfigWithValidButExpiredToken(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	ls := &loginState{
 		ClientID: "antani-antani",
@@ -181,10 +189,10 @@ func TestPsiphonConfigWithValidButExpiredToken(t *testing.T) {
 	if diff := cmp.Diff(expect, resp); diff != "" {
 		t.Fatal(diff)
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 0 {
+	if registerAPI.CountCall.Load() != 0 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -195,7 +203,8 @@ func TestPsiphonConfigWithRegisterAPIError(t *testing.T) {
 	ff.fill(&expect)
 	errMocked := errors.New("mocked error")
 	registerAPI := &FakeRegisterAPI{
-		Err: errMocked,
+		Err:       errMocked,
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginPsiphonConfigAPI{
 		API: &FakePsiphonConfigAPI{
@@ -204,7 +213,7 @@ func TestPsiphonConfigWithRegisterAPIError(t *testing.T) {
 			},
 		},
 		RegisterAPI: registerAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -216,7 +225,7 @@ func TestPsiphonConfigWithRegisterAPIError(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -229,10 +238,12 @@ func TestPsiphonConfigWithLoginFailure(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	errMocked := errors.New("mocked error")
 	loginAPI := &FakeLoginAPI{
-		Err: errMocked,
+		Err:       errMocked,
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginPsiphonConfigAPI{
 		API: &FakePsiphonConfigAPI{
@@ -242,7 +253,7 @@ func TestPsiphonConfigWithLoginFailure(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -254,10 +265,10 @@ func TestPsiphonConfigWithLoginFailure(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -270,12 +281,14 @@ func TestRegisterAndLoginPsiphonConfigThenFail(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	errMocked := errors.New("mocked error")
 	login := &withLoginPsiphonConfigAPI{
@@ -286,7 +299,7 @@ func TestRegisterAndLoginPsiphonConfigThenFail(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -298,17 +311,21 @@ func TestRegisterAndLoginPsiphonConfigThenFail(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
 
 func TestPsiphonConfigTheDatabaseIsReplaced(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -327,7 +344,7 @@ func TestPsiphonConfigTheDatabaseIsReplaced(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -342,10 +359,10 @@ func TestPsiphonConfigTheDatabaseIsReplaced(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -358,10 +375,10 @@ func TestPsiphonConfigTheDatabaseIsReplaced(t *testing.T) {
 	if resp == nil {
 		t.Fatal("expected non-nil response")
 	}
-	if handler.logins != 3 {
+	if handler.logins.Load() != 3 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 2 {
+	if handler.registers.Load() != 2 {
 		t.Fatal("invalid handler.registers")
 	}
 }
@@ -374,12 +391,14 @@ func TestRegisterAndLoginPsiphonConfigCannotWriteState(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	errMocked := errors.New("mocked error")
 	login := &withLoginPsiphonConfigAPI{
@@ -390,7 +409,7 @@ func TestRegisterAndLoginPsiphonConfigCannotWriteState(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 		JSONCodec: &FakeCodec{
 			EncodeErr: errMocked,
 		},
@@ -405,10 +424,10 @@ func TestRegisterAndLoginPsiphonConfigCannotWriteState(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -419,7 +438,7 @@ func TestPsiphonConfigReadStateDecodeFailure(t *testing.T) {
 	ff.fill(&expect)
 	errMocked := errors.New("mocked error")
 	login := &withLoginPsiphonConfigAPI{
-		KVStore:   &MemKVStore{},
+		KVStore:   &kvstore.Memory{},
 		JSONCodec: &FakeCodec{DecodeErr: errMocked},
 	}
 	ls := &loginState{
@@ -442,7 +461,11 @@ func TestPsiphonConfigReadStateDecodeFailure(t *testing.T) {
 
 func TestPsiphonConfigTheDatabaseIsReplacedThenFailure(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -461,7 +484,7 @@ func TestPsiphonConfigTheDatabaseIsReplacedThenFailure(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -476,10 +499,10 @@ func TestPsiphonConfigTheDatabaseIsReplacedThenFailure(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -494,17 +517,21 @@ func TestPsiphonConfigTheDatabaseIsReplacedThenFailure(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if handler.logins != 2 {
+	if handler.logins.Load() != 2 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 2 {
+	if handler.registers.Load() != 2 {
 		t.Fatal("invalid handler.registers")
 	}
 }
 
 func TestPsiphonConfigClockIsOffThenSuccess(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -523,7 +550,7 @@ func TestPsiphonConfigClockIsOffThenSuccess(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -538,10 +565,10 @@ func TestPsiphonConfigClockIsOffThenSuccess(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -556,17 +583,21 @@ func TestPsiphonConfigClockIsOffThenSuccess(t *testing.T) {
 	if resp == nil {
 		t.Fatal("expected non-nil response")
 	}
-	if handler.logins != 2 {
+	if handler.logins.Load() != 2 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 1 {
+	if handler.registers.Load() != 1 {
 		t.Fatal("invalid handler.registers")
 	}
 }
 
 func TestPsiphonConfigClockIsOffThen401(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -585,7 +616,7 @@ func TestPsiphonConfigClockIsOffThen401(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -600,10 +631,10 @@ func TestPsiphonConfigClockIsOffThen401(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -619,17 +650,21 @@ func TestPsiphonConfigClockIsOffThen401(t *testing.T) {
 	if resp == nil {
 		t.Fatal("expected non-nil response")
 	}
-	if handler.logins != 3 {
+	if handler.logins.Load() != 3 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 2 {
+	if handler.registers.Load() != 2 {
 		t.Fatal("invalid handler.registers")
 	}
 }
 
 func TestPsiphonConfigClockIsOffThen500(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -648,7 +683,7 @@ func TestPsiphonConfigClockIsOffThen500(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.PsiphonConfigRequest
 	ff.fill(&req)
@@ -663,10 +698,10 @@ func TestPsiphonConfigClockIsOffThen500(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -682,10 +717,10 @@ func TestPsiphonConfigClockIsOffThen500(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if handler.logins != 2 {
+	if handler.logins.Load() != 2 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 1 {
+	if handler.registers.Load() != 1 {
 		t.Fatal("invalid handler.registers")
 	}
 }
@@ -698,12 +733,14 @@ func TestRegisterAndLoginTorTargetsSuccess(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginTorTargetsAPI{
 		API: &FakeTorTargetsAPI{
@@ -713,7 +750,7 @@ func TestRegisterAndLoginTorTargetsSuccess(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -728,10 +765,10 @@ func TestRegisterAndLoginTorTargetsSuccess(t *testing.T) {
 	if diff := cmp.Diff(expect, resp); diff != "" {
 		t.Fatal(diff)
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -744,12 +781,14 @@ func TestTorTargetsContinueUsingToken(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginTorTargetsAPI{
 		API: &FakeTorTargetsAPI{
@@ -759,7 +798,7 @@ func TestTorTargetsContinueUsingToken(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -777,10 +816,10 @@ func TestTorTargetsContinueUsingToken(t *testing.T) {
 		if diff := cmp.Diff(expect, resp); diff != "" {
 			t.Fatal(diff)
 		}
-		if loginAPI.CountCall != 1 {
+		if loginAPI.CountCall.Load() != 1 {
 			t.Fatal("invalid loginAPI.CountCall")
 		}
-		if registerAPI.CountCall != 1 {
+		if registerAPI.CountCall.Load() != 1 {
 			t.Fatal("invalid registerAPI.CountCall")
 		}
 	}
@@ -801,10 +840,10 @@ func TestTorTargetsContinueUsingToken(t *testing.T) {
 	if diff := cmp.Diff(expect, resp); diff != "" {
 		t.Fatal(diff)
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -815,13 +854,15 @@ func TestTorTargetsWithValidButExpiredToken(t *testing.T) {
 	ff.fill(&expect)
 	errMocked := errors.New("mocked error")
 	registerAPI := &FakeRegisterAPI{
-		Err: errMocked,
+		Err:       errMocked,
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginTorTargetsAPI{
 		API: &FakeTorTargetsAPI{
@@ -831,7 +872,7 @@ func TestTorTargetsWithValidButExpiredToken(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	ls := &loginState{
 		ClientID: "antani-antani",
@@ -855,10 +896,10 @@ func TestTorTargetsWithValidButExpiredToken(t *testing.T) {
 	if diff := cmp.Diff(expect, resp); diff != "" {
 		t.Fatal(diff)
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 0 {
+	if registerAPI.CountCall.Load() != 0 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -869,7 +910,8 @@ func TestTorTargetsWithRegisterAPIError(t *testing.T) {
 	ff.fill(&expect)
 	errMocked := errors.New("mocked error")
 	registerAPI := &FakeRegisterAPI{
-		Err: errMocked,
+		Err:       errMocked,
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginTorTargetsAPI{
 		API: &FakeTorTargetsAPI{
@@ -878,7 +920,7 @@ func TestTorTargetsWithRegisterAPIError(t *testing.T) {
 			},
 		},
 		RegisterAPI: registerAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -890,7 +932,7 @@ func TestTorTargetsWithRegisterAPIError(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -903,10 +945,12 @@ func TestTorTargetsWithLoginFailure(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	errMocked := errors.New("mocked error")
 	loginAPI := &FakeLoginAPI{
-		Err: errMocked,
+		Err:       errMocked,
+		CountCall: &atomicx.Int64{},
 	}
 	login := &withLoginTorTargetsAPI{
 		API: &FakeTorTargetsAPI{
@@ -916,7 +960,7 @@ func TestTorTargetsWithLoginFailure(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -928,10 +972,10 @@ func TestTorTargetsWithLoginFailure(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -944,12 +988,14 @@ func TestRegisterAndLoginTorTargetsThenFail(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	errMocked := errors.New("mocked error")
 	login := &withLoginTorTargetsAPI{
@@ -960,7 +1006,7 @@ func TestRegisterAndLoginTorTargetsThenFail(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -972,17 +1018,21 @@ func TestRegisterAndLoginTorTargetsThenFail(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
 
 func TestTorTargetsTheDatabaseIsReplaced(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -1001,7 +1051,7 @@ func TestTorTargetsTheDatabaseIsReplaced(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -1016,10 +1066,10 @@ func TestTorTargetsTheDatabaseIsReplaced(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -1032,10 +1082,10 @@ func TestTorTargetsTheDatabaseIsReplaced(t *testing.T) {
 	if resp == nil {
 		t.Fatal("expected non-nil response")
 	}
-	if handler.logins != 3 {
+	if handler.logins.Load() != 3 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 2 {
+	if handler.registers.Load() != 2 {
 		t.Fatal("invalid handler.registers")
 	}
 }
@@ -1048,12 +1098,14 @@ func TestRegisterAndLoginTorTargetsCannotWriteState(t *testing.T) {
 		Response: &apimodel.RegisterResponse{
 			ClientID: "antani-antani",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	loginAPI := &FakeLoginAPI{
 		Response: &apimodel.LoginResponse{
 			Expire: time.Now().Add(3600 * time.Second),
 			Token:  "antani-antani-token",
 		},
+		CountCall: &atomicx.Int64{},
 	}
 	errMocked := errors.New("mocked error")
 	login := &withLoginTorTargetsAPI{
@@ -1064,7 +1116,7 @@ func TestRegisterAndLoginTorTargetsCannotWriteState(t *testing.T) {
 		},
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 		JSONCodec: &FakeCodec{
 			EncodeErr: errMocked,
 		},
@@ -1079,10 +1131,10 @@ func TestRegisterAndLoginTorTargetsCannotWriteState(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if loginAPI.CountCall != 1 {
+	if loginAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid loginAPI.CountCall")
 	}
-	if registerAPI.CountCall != 1 {
+	if registerAPI.CountCall.Load() != 1 {
 		t.Fatal("invalid registerAPI.CountCall")
 	}
 }
@@ -1093,7 +1145,7 @@ func TestTorTargetsReadStateDecodeFailure(t *testing.T) {
 	ff.fill(&expect)
 	errMocked := errors.New("mocked error")
 	login := &withLoginTorTargetsAPI{
-		KVStore:   &MemKVStore{},
+		KVStore:   &kvstore.Memory{},
 		JSONCodec: &FakeCodec{DecodeErr: errMocked},
 	}
 	ls := &loginState{
@@ -1116,7 +1168,11 @@ func TestTorTargetsReadStateDecodeFailure(t *testing.T) {
 
 func TestTorTargetsTheDatabaseIsReplacedThenFailure(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -1135,7 +1191,7 @@ func TestTorTargetsTheDatabaseIsReplacedThenFailure(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -1150,10 +1206,10 @@ func TestTorTargetsTheDatabaseIsReplacedThenFailure(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -1168,17 +1224,21 @@ func TestTorTargetsTheDatabaseIsReplacedThenFailure(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if handler.logins != 2 {
+	if handler.logins.Load() != 2 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 2 {
+	if handler.registers.Load() != 2 {
 		t.Fatal("invalid handler.registers")
 	}
 }
 
 func TestTorTargetsClockIsOffThenSuccess(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -1197,7 +1257,7 @@ func TestTorTargetsClockIsOffThenSuccess(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -1212,10 +1272,10 @@ func TestTorTargetsClockIsOffThenSuccess(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -1230,17 +1290,21 @@ func TestTorTargetsClockIsOffThenSuccess(t *testing.T) {
 	if resp == nil {
 		t.Fatal("expected non-nil response")
 	}
-	if handler.logins != 2 {
+	if handler.logins.Load() != 2 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 1 {
+	if handler.registers.Load() != 1 {
 		t.Fatal("invalid handler.registers")
 	}
 }
 
 func TestTorTargetsClockIsOffThen401(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -1259,7 +1323,7 @@ func TestTorTargetsClockIsOffThen401(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -1274,10 +1338,10 @@ func TestTorTargetsClockIsOffThen401(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -1293,17 +1357,21 @@ func TestTorTargetsClockIsOffThen401(t *testing.T) {
 	if resp == nil {
 		t.Fatal("expected non-nil response")
 	}
-	if handler.logins != 3 {
+	if handler.logins.Load() != 3 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 2 {
+	if handler.registers.Load() != 2 {
 		t.Fatal("invalid handler.registers")
 	}
 }
 
 func TestTorTargetsClockIsOffThen500(t *testing.T) {
 	ff := &fakeFill{}
-	handler := &LoginHandler{t: t}
+	handler := &LoginHandler{
+		logins:    &atomicx.Int64{},
+		registers: &atomicx.Int64{},
+		t:         t,
+	}
 	srvr := httptest.NewServer(handler)
 	defer srvr.Close()
 	registerAPI := &simpleRegisterAPI{
@@ -1322,7 +1390,7 @@ func TestTorTargetsClockIsOffThen500(t *testing.T) {
 		API:         baseAPI,
 		RegisterAPI: registerAPI,
 		LoginAPI:    loginAPI,
-		KVStore:     &MemKVStore{},
+		KVStore:     &kvstore.Memory{},
 	}
 	var req *apimodel.TorTargetsRequest
 	ff.fill(&req)
@@ -1337,10 +1405,10 @@ func TestTorTargetsClockIsOffThen500(t *testing.T) {
 		if resp == nil {
 			t.Fatal("expected non-nil response")
 		}
-		if handler.logins != 1 {
+		if handler.logins.Load() != 1 {
 			t.Fatal("invalid handler.logins")
 		}
-		if handler.registers != 1 {
+		if handler.registers.Load() != 1 {
 			t.Fatal("invalid handler.registers")
 		}
 	}
@@ -1356,10 +1424,10 @@ func TestTorTargetsClockIsOffThen500(t *testing.T) {
 	if resp != nil {
 		t.Fatal("expected nil response")
 	}
-	if handler.logins != 2 {
+	if handler.logins.Load() != 2 {
 		t.Fatal("invalid handler.logins")
 	}
-	if handler.registers != 1 {
+	if handler.registers.Load() != 1 {
 		t.Fatal("invalid handler.registers")
 	}
 }
diff --git a/internal/engine/ooapi/loginhandler_test.go b/internal/ooapi/loginhandler_test.go
similarity index 94%
rename from internal/engine/ooapi/loginhandler_test.go
rename to internal/ooapi/loginhandler_test.go
index f9e0274..3ceac37 100644
--- a/internal/engine/ooapi/loginhandler_test.go
+++ b/internal/ooapi/loginhandler_test.go
@@ -6,11 +6,11 @@ import (
 	"net/http"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"testing"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 // LoginHandler is an http.Handler to test login
@@ -20,8 +20,8 @@ type LoginHandler struct {
 	noRegister   bool
 	state        []*loginState
 	t            *testing.T
-	logins       int32
-	registers    int32
+	logins       *atomicx.Int64
+	registers    *atomicx.Int64
 }
 
 func (lh *LoginHandler) forgetLogins() {
@@ -49,10 +49,14 @@ func (lh *LoginHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// for simplicity since it's already tested.
 	switch r.URL.Path {
 	case "/api/v1/register":
-		atomic.AddInt32(&lh.registers, 1)
+		if lh.registers != nil {
+			lh.registers.Add(1)
+		}
 		lh.register(w, r)
 	case "/api/v1/login":
-		atomic.AddInt32(&lh.logins, 1)
+		if lh.logins != nil {
+			lh.logins.Add(1)
+		}
 		lh.login(w, r)
 	case "/api/v1/test-list/psiphon-config":
 		lh.psiphon(w, r)
diff --git a/internal/engine/ooapi/loginmodel.go b/internal/ooapi/loginmodel.go
similarity index 93%
rename from internal/engine/ooapi/loginmodel.go
rename to internal/ooapi/loginmodel.go
index 4337348..5d86a5c 100644
--- a/internal/engine/ooapi/loginmodel.go
+++ b/internal/ooapi/loginmodel.go
@@ -5,8 +5,8 @@ import (
 	"encoding/base64"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // loginState is the struct saved in the kvstore
diff --git a/internal/engine/ooapi/requests.go b/internal/ooapi/requests.go
similarity index 98%
rename from internal/engine/ooapi/requests.go
rename to internal/ooapi/requests.go
index ab0c0af..7f23cdb 100644
--- a/internal/engine/ooapi/requests.go
+++ b/internal/ooapi/requests.go
@@ -11,7 +11,7 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func (api *simpleCheckReportIDAPI) newRequest(ctx context.Context, req *apimodel.CheckReportIDRequest) (*http.Request, error) {
diff --git a/internal/engine/ooapi/responses.go b/internal/ooapi/responses.go
similarity index 99%
rename from internal/engine/ooapi/responses.go
rename to internal/ooapi/responses.go
index f843040..da6078c 100644
--- a/internal/engine/ooapi/responses.go
+++ b/internal/ooapi/responses.go
@@ -10,7 +10,7 @@ import (
 	"io/ioutil"
 	"net/http"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/apimodel"
 )
 
 func (api *simpleCheckReportIDAPI) newResponse(resp *http.Response, err error) (*apimodel.CheckReportIDResponse, error) {
diff --git a/internal/engine/ooapi/swagger_test.go b/internal/ooapi/swagger_test.go
similarity index 100%
rename from internal/engine/ooapi/swagger_test.go
rename to internal/ooapi/swagger_test.go
diff --git a/internal/engine/ooapi/swaggerdiff_test.go b/internal/ooapi/swaggerdiff_test.go
similarity index 98%
rename from internal/engine/ooapi/swaggerdiff_test.go
rename to internal/ooapi/swaggerdiff_test.go
index 6715bc9..d805223 100644
--- a/internal/engine/ooapi/swaggerdiff_test.go
+++ b/internal/ooapi/swaggerdiff_test.go
@@ -13,7 +13,7 @@ import (
 	"github.com/hexops/gotextdiff"
 	"github.com/hexops/gotextdiff/myers"
 	"github.com/hexops/gotextdiff/span"
-	"github.com/ooni/probe-cli/v3/internal/engine/ooapi/internal/openapi"
+	"github.com/ooni/probe-cli/v3/internal/ooapi/internal/openapi"
 )
 
 const (
diff --git a/internal/engine/ooapi/utils.go b/internal/ooapi/utils.go
similarity index 100%
rename from internal/engine/ooapi/utils.go
rename to internal/ooapi/utils.go
diff --git a/internal/engine/ooapi/utils_test.go b/internal/ooapi/utils_test.go
similarity index 100%
rename from internal/engine/ooapi/utils_test.go
rename to internal/ooapi/utils_test.go
diff --git a/internal/engine/internal/platform/platform.go b/internal/platform/platform.go
similarity index 98%
rename from internal/engine/internal/platform/platform.go
rename to internal/platform/platform.go
index 5641331..39d6fe2 100644
--- a/internal/engine/internal/platform/platform.go
+++ b/internal/platform/platform.go
@@ -7,10 +7,15 @@ import "runtime"
 // Name returns the platform name. The returned value is one of:
 //
 // 1. "android"
+//
 // 2. "ios"
+//
 // 3. "linux"
+//
 // 5. "macos"
+//
 // 4. "windows"
+//
 // 5. "unknown"
 //
 // The android, ios, linux, macos, windows, and unknown strings are
diff --git a/internal/engine/internal/platform/platform_cgo.go b/internal/platform/platform_cgo.go
similarity index 100%
rename from internal/engine/internal/platform/platform_cgo.go
rename to internal/platform/platform_cgo.go
diff --git a/internal/engine/internal/platform/platform_otherwise.go b/internal/platform/platform_otherwise.go
similarity index 100%
rename from internal/engine/internal/platform/platform_otherwise.go
rename to internal/platform/platform_otherwise.go
diff --git a/internal/engine/internal/platform/platform_test.go b/internal/platform/platform_test.go
similarity index 100%
rename from internal/engine/internal/platform/platform_test.go
rename to internal/platform/platform_test.go
diff --git a/internal/engine/internal/randx/randx.go b/internal/randx/randx.go
similarity index 79%
rename from internal/engine/internal/randx/randx.go
rename to internal/randx/randx.go
index 7d240e9..01af8ac 100644
--- a/internal/engine/internal/randx/randx.go
+++ b/internal/randx/randx.go
@@ -1,4 +1,4 @@
-// Package randx contains math/rand extensions
+// Package randx contains math/rand extensions.
 package randx
 
 import (
@@ -7,14 +7,16 @@ import (
 	"unicode"
 )
 
+// These constants are used by lettersWithString.
 const (
 	uppercase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 	lowercase = "abcdefghijklmnopqrstuvwxyz"
 	letters   = uppercase + lowercase
 )
 
+// lettersWithString is a method for generating a random string
+// described at https://stackoverflow.com/questions/22892120.
 func lettersWithString(n int, letterBytes string) string {
-	// See https://stackoverflow.com/questions/22892120
 	rnd := rand.New(rand.NewSource(time.Now().UnixNano()))
 	b := make([]byte, n)
 	for i := range b {
@@ -23,12 +25,12 @@ func lettersWithString(n int, letterBytes string) string {
 	return string(b)
 }
 
-// Letters return a string composed of random letters
+// Letters return a string composed of random letters.
 func Letters(n int) string {
 	return lettersWithString(n, letters)
 }
 
-// LettersUppercase return a string composed of random uppercase letters
+// LettersUppercase return a string composed of random uppercase letters.
 func LettersUppercase(n int) string {
 	return lettersWithString(n, uppercase)
 }
diff --git a/internal/engine/internal/randx/randx_test.go b/internal/randx/randx_test.go
similarity index 63%
rename from internal/engine/internal/randx/randx_test.go
rename to internal/randx/randx_test.go
index e8c8417..71f8584 100644
--- a/internal/engine/internal/randx/randx_test.go
+++ b/internal/randx/randx_test.go
@@ -1,13 +1,9 @@
-package randx_test
+package randx
 
-import (
-	"testing"
-
-	"github.com/ooni/probe-cli/v3/internal/engine/internal/randx"
-)
+import "testing"
 
 func TestLetters(t *testing.T) {
-	str := randx.Letters(1024)
+	str := Letters(1024)
 	for _, chr := range str {
 		if (chr >= 'A' && chr <= 'Z') || (chr >= 'a' && chr <= 'z') {
 			continue
@@ -17,7 +13,7 @@ func TestLetters(t *testing.T) {
 }
 
 func TestLettersUppercase(t *testing.T) {
-	str := randx.LettersUppercase(1024)
+	str := LettersUppercase(1024)
 	for _, chr := range str {
 		if chr >= 'A' && chr <= 'Z' {
 			continue
@@ -27,8 +23,8 @@ func TestLettersUppercase(t *testing.T) {
 }
 
 func TestChangeCapitalization(t *testing.T) {
-	str := randx.Letters(2048)
-	if randx.ChangeCapitalization(str) == str {
+	str := Letters(2048)
+	if ChangeCapitalization(str) == str {
 		t.Fatal("capitalization not changed")
 	}
 }
diff --git a/internal/engine/runtimex/runtimex.go b/internal/runtimex/runtimex.go
similarity index 60%
rename from internal/engine/runtimex/runtimex.go
rename to internal/runtimex/runtimex.go
index 79dc5eb..6d454e4 100644
--- a/internal/engine/runtimex/runtimex.go
+++ b/internal/runtimex/runtimex.go
@@ -1,10 +1,10 @@
-// Package runtimex contains runtime extensions. This package is inspired to the excellent
-// github.com/m-lab/rtx package, except that it's simpler.
+// Package runtimex contains runtime extensions. This package is inspired to
+// https://pkg.go.dev/github.com/m-lab/go/rtx, except that it's simpler.
 package runtimex
 
 import "fmt"
 
-// PanicOnError panics if err is not nil.
+// PanicOnError calls panic() if err is not nil.
 func PanicOnError(err error, message string) {
 	if err != nil {
 		panic(fmt.Errorf("%s: %w", message, err))
diff --git a/internal/engine/runtimex/runtimex_test.go b/internal/runtimex/runtimex_test.go
similarity index 88%
rename from internal/engine/runtimex/runtimex_test.go
rename to internal/runtimex/runtimex_test.go
index 19a29c4..9b129ec 100644
--- a/internal/engine/runtimex/runtimex_test.go
+++ b/internal/runtimex/runtimex_test.go
@@ -4,7 +4,7 @@ import (
 	"errors"
 	"testing"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 func TestGood(t *testing.T) {
diff --git a/internal/engine/shellx/shellx.go b/internal/shellx/shellx.go
similarity index 55%
rename from internal/engine/shellx/shellx.go
rename to internal/shellx/shellx.go
index f95e71f..94e6cd4 100644
--- a/internal/engine/shellx/shellx.go
+++ b/internal/shellx/shellx.go
@@ -1,4 +1,4 @@
-// Package shellx contains utilities to run external commands.
+// Package shellx runs external commands.
 package shellx
 
 import (
@@ -6,24 +6,36 @@ import (
 	"os"
 	"strings"
 
-	"golang.org/x/sys/execabs"
-
 	"github.com/apex/log"
 	"github.com/google/shlex"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"golang.org/x/sys/execabs"
 )
 
+// runconfig is the configuration for run.
 type runconfig struct {
-	args     []string
+	// args contains the command line arguments.
+	args []string
+
+	// command is the command to execute.
+	command string
+
+	// loginfof is the logging function.
 	loginfof func(format string, v ...interface{})
-	name     string
-	stdout   *os.File
-	stderr   *os.File
+
+	// stdout is the standard output.
+	stdout *os.File
+
+	// stderr is the standard error.
+	stderr *os.File
 }
 
+// run is the internal function for running commands.
 func run(config runconfig) error {
-	config.loginfof("exec: %s %s", config.name, strings.Join(config.args, " "))
-	cmd := execabs.Command(config.name, config.args...)
+	config.loginfof(
+		"exec: %s %s", config.command, strings.Join(config.args, " "))
+	// implementation note: here we're using execabs because
+	// of https://blog.golang.org/path-security.
+	cmd := execabs.Command(config.command, config.args...)
 	cmd.Stdout = config.stdout
 	cmd.Stderr = config.stderr
 	err := cmd.Run()
@@ -35,26 +47,29 @@ func run(config runconfig) error {
 func Run(name string, arg ...string) error {
 	return run(runconfig{
 		args:     arg,
+		command:  name,
 		loginfof: log.Log.Infof,
-		name:     name,
 		stdout:   os.Stdout,
 		stderr:   os.Stderr,
 	})
 }
 
+// quietInfof is an infof function that does nothing.
+func quietInfof(format string, v ...interface{}) {}
+
 // RunQuiet is like Run but it does not emit any output.
 func RunQuiet(name string, arg ...string) error {
 	return run(runconfig{
 		args:     arg,
-		loginfof: model.DiscardLogger.Infof,
-		name:     name,
+		command:  name,
+		loginfof: quietInfof,
 		stdout:   nil,
 		stderr:   nil,
 	})
 }
 
 // RunCommandline is like Run but its only argument is a command
-// line that will be splitted using the google/shlex package
+// line that will be splitted using the google/shlex package.
 func RunCommandline(cmdline string) error {
 	args, err := shlex.Split(cmdline)
 	if err != nil {
diff --git a/internal/engine/shellx/shellx_test.go b/internal/shellx/shellx_test.go
similarity index 100%
rename from internal/engine/shellx/shellx_test.go
rename to internal/shellx/shellx_test.go
diff --git a/pkg/oonimkall/experiment_test.go b/pkg/oonimkall/experiment_test.go
index 3a9a732..8ff2779 100644
--- a/pkg/oonimkall/experiment_test.go
+++ b/pkg/oonimkall/experiment_test.go
@@ -3,8 +3,8 @@ package oonimkall
 import (
 	"context"
 	"sync"
-	"sync/atomic"
 
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 )
 
@@ -17,16 +17,18 @@ func (cb *FakeExperimentCallbacks) OnProgress(percentage float64, message string
 // FakeExperimentSession is a fake experimentSession
 type FakeExperimentSession struct {
 	ExperimentBuilder       experimentBuilder
-	LockCount               int32
+	LockCount               *atomicx.Int64
 	LookupBackendsErr       error
 	LookupLocationErr       error
 	NewExperimentBuilderErr error
-	UnlockCount             int32
+	UnlockCount             *atomicx.Int64
 }
 
 // lock implements experimentSession.lock
 func (sess *FakeExperimentSession) lock() {
-	atomic.AddInt32(&sess.LockCount, 1)
+	if sess.LockCount != nil {
+		sess.LockCount.Add(1)
+	}
 }
 
 // maybeLookupBackends implements experimentSession.maybeLookupBackends
@@ -46,7 +48,9 @@ func (sess *FakeExperimentSession) newExperimentBuilder(name string) (experiment
 
 // unlock implements experimentSession.unlock
 func (sess *FakeExperimentSession) unlock() {
-	atomic.AddInt32(&sess.UnlockCount, 1)
+	if sess.UnlockCount != nil {
+		sess.UnlockCount.Add(1)
+	}
 }
 
 // FakeExperimentBuilder is a fake experimentBuilder
diff --git a/pkg/oonimkall/internal/tasks/runner.go b/pkg/oonimkall/internal/tasks/runner.go
index ebff330..d98a02b 100644
--- a/pkg/oonimkall/internal/tasks/runner.go
+++ b/pkg/oonimkall/internal/tasks/runner.go
@@ -8,9 +8,10 @@ import (
 	"net/url"
 	"time"
 
-	engine "github.com/ooni/probe-cli/v3/internal/engine"
+	"github.com/ooni/probe-cli/v3/internal/engine"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 const (
@@ -71,7 +72,7 @@ func (r *Runner) hasUnsupportedSettings(logger *ChanLogger) bool {
 }
 
 func (r *Runner) newsession(ctx context.Context, logger *ChanLogger) (*engine.Session, error) {
-	kvstore, err := engine.NewFileSystemKVStore(r.settings.StateDir)
+	kvstore, err := kvstore.NewFS(r.settings.StateDir)
 	if err != nil {
 		return nil, err
 	}
diff --git a/pkg/oonimkall/session.go b/pkg/oonimkall/session.go
index 059abae..da63b02 100644
--- a/pkg/oonimkall/session.go
+++ b/pkg/oonimkall/session.go
@@ -8,12 +8,13 @@ import (
 	"runtime"
 	"sync"
 
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine"
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/assetsdir"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // AtomicInt64 allows us to export atomicx.Int64 variables to
@@ -25,8 +26,8 @@ type AtomicInt64 struct {
 // These two variables contain metrics pertaining to the number
 // of Sessions and Contexts that are currently being used.
 var (
-	ActiveSessions = &AtomicInt64{atomicx.NewInt64()}
-	ActiveContexts = &AtomicInt64{atomicx.NewInt64()}
+	ActiveSessions = &AtomicInt64{&atomicx.Int64{}}
+	ActiveContexts = &AtomicInt64{&atomicx.Int64{}}
 )
 
 // Logger is the logger used by a Session. You should implement a class
@@ -147,7 +148,7 @@ func NewSessionWithContext(ctx *Context, config *SessionConfig) (*Session, error
 
 // newSessionWithContext implements NewSessionWithContext.
 func newSessionWithContext(ctx context.Context, config *SessionConfig) (*Session, error) {
-	kvstore, err := engine.NewFileSystemKVStore(config.StateDir)
+	kvstore, err := kvstore.NewFS(config.StateDir)
 	if err != nil {
 		return nil, err
 	}
diff --git a/pkg/oonimkall/sessioncontext_test.go b/pkg/oonimkall/sessioncontext_test.go
index 0d3a96b..6945b8d 100644
--- a/pkg/oonimkall/sessioncontext_test.go
+++ b/pkg/oonimkall/sessioncontext_test.go
@@ -4,7 +4,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
 func TestClampTimeout(t *testing.T) {
@@ -26,7 +26,7 @@ func TestClampTimeout(t *testing.T) {
 }
 
 func TestNewContextWithZeroTimeout(t *testing.T) {
-	here := atomicx.NewInt64()
+	here := &atomicx.Int64{}
 	ctx, cancel := newContext(0)
 	defer cancel()
 	go func() {
@@ -41,7 +41,7 @@ func TestNewContextWithZeroTimeout(t *testing.T) {
 }
 
 func TestNewContextWithNegativeTimeout(t *testing.T) {
-	here := atomicx.NewInt64()
+	here := &atomicx.Int64{}
 	ctx, cancel := newContext(-1)
 	defer cancel()
 	go func() {
@@ -56,7 +56,7 @@ func TestNewContextWithNegativeTimeout(t *testing.T) {
 }
 
 func TestNewContextWithHugeTimeout(t *testing.T) {
-	here := atomicx.NewInt64()
+	here := &atomicx.Int64{}
 	ctx, cancel := newContext(maxTimeout + 1)
 	defer cancel()
 	go func() {
@@ -71,7 +71,7 @@ func TestNewContextWithHugeTimeout(t *testing.T) {
 }
 
 func TestNewContextWithReasonableTimeout(t *testing.T) {
-	here := atomicx.NewInt64()
+	here := &atomicx.Int64{}
 	ctx, cancel := newContext(1)
 	defer cancel()
 	go func() {
@@ -86,7 +86,7 @@ func TestNewContextWithReasonableTimeout(t *testing.T) {
 }
 
 func TestNewContextWithArtificiallyLowMaxTimeout(t *testing.T) {
-	here := atomicx.NewInt64()
+	here := &atomicx.Int64{}
 	const maxTimeout = 2
 	ctx, cancel := newContextEx(maxTimeout+1, maxTimeout)
 	defer cancel()
diff --git a/pkg/oonimkall/task.go b/pkg/oonimkall/task.go
index 1ad82db..07c3c9e 100644
--- a/pkg/oonimkall/task.go
+++ b/pkg/oonimkall/task.go
@@ -43,8 +43,8 @@ import (
 	"context"
 	"encoding/json"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/atomicx"
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/pkg/oonimkall/internal/tasks"
 )
 
@@ -77,8 +77,8 @@ func StartTask(input string) (*Task, error) {
 	ctx, cancel := context.WithCancel(context.Background())
 	task := &Task{
 		cancel:    cancel,
-		isdone:    atomicx.NewInt64(),
-		isstopped: atomicx.NewInt64(),
+		isdone:    &atomicx.Int64{},
+		isstopped: &atomicx.Int64{},
 		out:       make(chan *tasks.Event, bufsiz),
 	}
 	go func() {
diff --git a/pkg/oonimkall/webconnectivity.go b/pkg/oonimkall/webconnectivity.go
index 4a393e2..e96df38 100644
--- a/pkg/oonimkall/webconnectivity.go
+++ b/pkg/oonimkall/webconnectivity.go
@@ -4,7 +4,7 @@ import (
 	"context"
 	"encoding/json"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/runtimex"
 )
 
 // WebConnectivityConfig contains settings for WebConnectivity.
diff --git a/pkg/oonimkall/webconnectivity_test.go b/pkg/oonimkall/webconnectivity_test.go
index 7326b13..795e3cc 100644
--- a/pkg/oonimkall/webconnectivity_test.go
+++ b/pkg/oonimkall/webconnectivity_test.go
@@ -7,12 +7,17 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/model"
 )
 
 func TestWebConnectivityRunnerWithMaybeLookupBackendsFailure(t *testing.T) {
 	errMocked := errors.New("mocked error")
-	sess := &FakeExperimentSession{LookupBackendsErr: errMocked}
+	sess := &FakeExperimentSession{
+		LockCount:         &atomicx.Int64{},
+		LookupBackendsErr: errMocked,
+		UnlockCount:       &atomicx.Int64{},
+	}
 	runner := &webConnectivityRunner{sess: sess}
 	ctx := context.Background()
 	config := &WebConnectivityConfig{Input: "https://ooni.org"}
@@ -23,14 +28,18 @@ func TestWebConnectivityRunnerWithMaybeLookupBackendsFailure(t *testing.T) {
 	if out != nil {
 		t.Fatal("expected nil here")
 	}
-	if sess.LockCount != 1 || sess.UnlockCount != 1 {
+	if sess.LockCount.Load() != 1 || sess.UnlockCount.Load() != 1 {
 		t.Fatal("invalid locking pattern")
 	}
 }
 
 func TestWebConnectivityRunnerWithMaybeLookupLocationFailure(t *testing.T) {
 	errMocked := errors.New("mocked error")
-	sess := &FakeExperimentSession{LookupLocationErr: errMocked}
+	sess := &FakeExperimentSession{
+		LockCount:         &atomicx.Int64{},
+		LookupLocationErr: errMocked,
+		UnlockCount:       &atomicx.Int64{},
+	}
 	runner := &webConnectivityRunner{sess: sess}
 	ctx := context.Background()
 	config := &WebConnectivityConfig{Input: "https://ooni.org"}
@@ -41,14 +50,18 @@ func TestWebConnectivityRunnerWithMaybeLookupLocationFailure(t *testing.T) {
 	if out != nil {
 		t.Fatal("expected nil here")
 	}
-	if sess.LockCount != 1 || sess.UnlockCount != 1 {
+	if sess.LockCount.Load() != 1 || sess.UnlockCount.Load() != 1 {
 		t.Fatal("invalid locking pattern")
 	}
 }
 
 func TestWebConnectivityRunnerWithNewExperimentBuilderFailure(t *testing.T) {
 	errMocked := errors.New("mocked error")
-	sess := &FakeExperimentSession{NewExperimentBuilderErr: errMocked}
+	sess := &FakeExperimentSession{
+		LockCount:               &atomicx.Int64{},
+		NewExperimentBuilderErr: errMocked,
+		UnlockCount:             &atomicx.Int64{},
+	}
 	runner := &webConnectivityRunner{sess: sess}
 	ctx := context.Background()
 	config := &WebConnectivityConfig{Input: "https://ooni.org"}
@@ -59,7 +72,7 @@ func TestWebConnectivityRunnerWithNewExperimentBuilderFailure(t *testing.T) {
 	if out != nil {
 		t.Fatal("expected nil here")
 	}
-	if sess.LockCount != 1 || sess.UnlockCount != 1 {
+	if sess.LockCount.Load() != 1 || sess.UnlockCount.Load() != 1 {
 		t.Fatal("invalid locking pattern")
 	}
 }
@@ -69,7 +82,11 @@ func TestWebConnectivityRunnerWithMeasureFailure(t *testing.T) {
 	cbs := &FakeExperimentCallbacks{}
 	e := &FakeExperiment{Err: errMocked}
 	eb := &FakeExperimentBuilder{Experiment: e}
-	sess := &FakeExperimentSession{ExperimentBuilder: eb}
+	sess := &FakeExperimentSession{
+		LockCount:         &atomicx.Int64{},
+		ExperimentBuilder: eb,
+		UnlockCount:       &atomicx.Int64{},
+	}
 	runner := &webConnectivityRunner{sess: sess}
 	ctx := context.Background()
 	config := &WebConnectivityConfig{
@@ -83,7 +100,7 @@ func TestWebConnectivityRunnerWithMeasureFailure(t *testing.T) {
 	if out != nil {
 		t.Fatal("expected nil here")
 	}
-	if sess.LockCount != 1 || sess.UnlockCount != 1 {
+	if sess.LockCount.Load() != 1 || sess.UnlockCount.Load() != 1 {
 		t.Fatal("invalid locking pattern")
 	}
 	if eb.Callbacks != cbs {
@@ -99,7 +116,11 @@ func TestWebConnectivityRunnerWithNoError(t *testing.T) {
 	cbs := &FakeExperimentCallbacks{}
 	e := &FakeExperiment{Measurement: m, Sent: 10, Received: 128}
 	eb := &FakeExperimentBuilder{Experiment: e}
-	sess := &FakeExperimentSession{ExperimentBuilder: eb}
+	sess := &FakeExperimentSession{
+		LockCount:         &atomicx.Int64{},
+		ExperimentBuilder: eb,
+		UnlockCount:       &atomicx.Int64{},
+	}
 	runner := &webConnectivityRunner{sess: sess}
 	ctx := context.Background()
 	config := &WebConnectivityConfig{
@@ -113,7 +134,7 @@ func TestWebConnectivityRunnerWithNoError(t *testing.T) {
 	if out == nil {
 		t.Fatal("expected non-nil here")
 	}
-	if sess.LockCount != 1 || sess.UnlockCount != 1 {
+	if sess.LockCount.Load() != 1 || sess.UnlockCount.Load() != 1 {
 		t.Fatal("invalid locking pattern")
 	}
 	if eb.Callbacks != cbs {