diff --git a/internal/domain/workerruntime/contract_external_test.go b/internal/domain/workerruntime/contract_external_test.go
new file mode 100644
index 0000000..2398e35
--- /dev/null
+++ b/internal/domain/workerruntime/contract_external_test.go
@@ -0,0 +1,24 @@
+package workerruntime_test
+
+import (
+	"testing"
+	"time"
+
+	"proxy-pool/internal/domain/workerruntime"
+	"proxy-pool/internal/domain/workerruntime/contracttest"
+)
+
+func TestMemoryStoreContract(t *testing.T) {
+	now := time.Date(2026, 7, 31, 9, 0, 0, 0, time.UTC)
+	contracttest.Run(t, func(t *testing.T) contracttest.Fixture {
+		t.Helper()
+		store, err := workerruntime.NewMemoryStore(func() time.Time { return now })
+		if err != nil {
+			t.Fatalf("NewMemoryStore(): %v", err)
+		}
+		return contracttest.Fixture{
+			Store: store, Reader: store,
+			Advance: func(duration time.Duration) { now = now.Add(duration) },
+		}
+	})
+}
diff --git a/internal/domain/workerruntime/contracttest/contract.go b/internal/domain/workerruntime/contracttest/contract.go
new file mode 100644
index 0000000..584fb5d
--- /dev/null
+++ b/internal/domain/workerruntime/contracttest/contract.go
@@ -0,0 +1,131 @@
+package contracttest
+
+import (
+	"context"
+	"crypto/sha256"
+	"errors"
+	"testing"
+	"time"
+
+	"proxy-pool/internal/domain/workerruntime"
+)
+
+type Fixture struct {
+	Store   workerruntime.ControlStore
+	Reader  workerruntime.RuntimeReader
+	Advance func(time.Duration)
+}
+
+type Factory func(*testing.T) Fixture
+
+// Run exercises the public control-store behavior shared by Memory and Redis.
+func Run(t *testing.T, factory Factory) {
+	t.Helper()
+	t.Run("acknowledged runtime lifecycle", func(t *testing.T) { runLifecycle(t, newFixture(t, factory)) })
+	t.Run("negative acknowledgement fences runtime", func(t *testing.T) { runNegativeAck(t, newFixture(t, factory)) })
+}
+
+func runLifecycle(t *testing.T, fixture Fixture) {
+	t.Helper()
+	ctx := context.Background()
+	open(t, fixture.Store)
+	epoch, err := fixture.Store.CurrentOwnershipEpoch(ctx)
+	if err != nil {
+		t.Fatalf("CurrentOwnershipEpoch(): %v", err)
+	}
+	reference := snapshot(7, epoch, "snapshot-7")
+	report := runtimeReport(1, 7, epoch)
+	if err := fixture.Store.ReplaceRuntime(ctx, report, time.Minute); !errors.Is(err, workerruntime.ErrSnapshotMismatch) {
+		t.Fatalf("ReplaceRuntime(before ACK) error = %v", err)
+	}
+	if err := fixture.Store.RecordIssuedSnapshot(ctx, reference, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(): %v", err)
+	}
+	ack := workerruntime.SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: reference, Applied: true}
+	if err := fixture.Store.AcknowledgeSnapshot(ctx, ack, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(): %v", err)
+	}
+	if err := fixture.Store.ReplaceRuntime(ctx, report, time.Minute); err != nil {
+		t.Fatalf("ReplaceRuntime(after ACK): %v", err)
+	}
+	assertFresh(t, fixture.Reader, epoch, true)
+	if err := fixture.Store.AcknowledgeSnapshot(ctx, ack, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(replay): %v", err)
+	}
+	if err := fixture.Store.ReplaceRuntime(ctx, runtimeReport(0, 7, epoch), time.Minute); !errors.Is(err, workerruntime.ErrInvalidReport) {
+		t.Fatalf("ReplaceRuntime(invalid sequence) error = %v", err)
+	}
+	fixture.Advance(2 * time.Minute)
+	assertFresh(t, fixture.Reader, epoch, false)
+}
+
+func runNegativeAck(t *testing.T, fixture Fixture) {
+	t.Helper()
+	ctx := context.Background()
+	open(t, fixture.Store)
+	epoch, err := fixture.Store.CurrentOwnershipEpoch(ctx)
+	if err != nil {
+		t.Fatalf("CurrentOwnershipEpoch(): %v", err)
+	}
+	first := snapshot(7, epoch, "snapshot-7")
+	if err := fixture.Store.RecordIssuedSnapshot(ctx, first, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(first): %v", err)
+	}
+	if err := fixture.Store.AcknowledgeSnapshot(ctx, workerruntime.SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: first, Applied: true}, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(first): %v", err)
+	}
+	second := snapshot(8, epoch, "snapshot-8")
+	if err := fixture.Store.RecordIssuedSnapshot(ctx, second, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(second): %v", err)
+	}
+	if err := fixture.Store.AcknowledgeSnapshot(ctx, workerruntime.SnapshotAcknowledgement{
+		WorkerID: "worker-a", SessionID: "session-a", Reference: second, ErrorCode: "apply_failed",
+	}, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(negative): %v", err)
+	}
+	if err := fixture.Store.ReplaceRuntime(ctx, runtimeReport(1, 7, epoch), time.Minute); !errors.Is(err, workerruntime.ErrSnapshotMismatch) {
+		t.Fatalf("ReplaceRuntime(delayed): %v", err)
+	}
+}
+
+func newFixture(t *testing.T, factory Factory) Fixture {
+	t.Helper()
+	fixture := factory(t)
+	if fixture.Store == nil || fixture.Reader == nil || fixture.Advance == nil {
+		t.Fatal("contract fixture is incomplete")
+	}
+	return fixture
+}
+
+func open(t *testing.T, store workerruntime.ControlStore) {
+	t.Helper()
+	err := store.OpenSession(context.Background(), workerruntime.Session{
+		WorkerID: "worker-a", InstanceID: "instance-a", SessionID: "session-a", Zone: "zone-a", ProtocolVersion: 1,
+	}, time.Minute)
+	if err != nil {
+		t.Fatalf("OpenSession(): %v", err)
+	}
+}
+
+func snapshot(version, epoch uint64, value string) workerruntime.SnapshotReference {
+	return workerruntime.SnapshotReference{
+		WorkerID: "worker-a", Version: version, OwnershipEpoch: epoch, Checksum: sha256.Sum256([]byte(value)),
+	}
+}
+
+func runtimeReport(sequence, version, epoch uint64) workerruntime.Report {
+	return workerruntime.Report{
+		WorkerID: "worker-a", SessionID: "session-a", Sequence: sequence, SnapshotVersion: version,
+		OwnershipEpoch: epoch, ObservedAt: time.Date(2026, 7, 31, 9, 0, 0, 0, time.UTC),
+	}
+}
+
+func assertFresh(t *testing.T, reader workerruntime.RuntimeReader, epoch uint64, want bool) {
+	t.Helper()
+	snapshots, err := reader.ReadRuntime(context.Background(), []workerruntime.OwnedProxy{{
+		ProxyID: "proxy-a", WorkerID: "worker-a", OwnershipEpoch: epoch,
+	}})
+	if err != nil || len(snapshots) != 1 || snapshots[0].Fresh != want {
+		t.Fatalf("ReadRuntime() = %+v, %v; want Fresh=%t", snapshots, err, want)
+	}
+}
diff --git a/internal/domain/workerruntime/memory.go b/internal/domain/workerruntime/memory.go
index bdcd89f..c72e4de 100644
--- a/internal/domain/workerruntime/memory.go
+++ b/internal/domain/workerruntime/memory.go
@@ -3,18 +3,17 @@ package workerruntime
 import (
 	"context"
 	"crypto/sha256"
-	"encoding/json"
-	"sort"
-	"strings"
 	"sync"
 	"time"
 )
 
 type MemoryStore struct {
-	mu       sync.Mutex
-	now      func() time.Time
-	sessions map[string]memorySession
-	reports  map[string]memoryReport
+	mu         sync.Mutex
+	now        func() time.Time
+	epoch      uint64
+	sessions   map[string]memorySession
+	references map[string]memoryReference
+	reports    map[string]memoryReport
 }
 
 type memorySession struct {
@@ -22,6 +21,11 @@ type memorySession struct {
 	expiresAt time.Time
 }
 
+type memoryReference struct {
+	value     SnapshotReference
+	expiresAt time.Time
+}
+
 type memoryReport struct {
 	value     Report
 	digest    [sha256.Size]byte
@@ -30,6 +34,7 @@ type memoryReport struct {
 }
 
 var (
+	_ ControlStore  = (*MemoryStore)(nil)
 	_ SessionWriter = (*MemoryStore)(nil)
 	_ ReportWriter  = (*MemoryStore)(nil)
 	_ RuntimeReader = (*MemoryStore)(nil)
@@ -40,33 +45,184 @@ func NewMemoryStore(now func() time.Time) (*MemoryStore, error) {
 		return nil, ErrInvalidStore
 	}
 	return &MemoryStore{
-		now: now, sessions: make(map[string]memorySession), reports: make(map[string]memoryReport),
+		now: now, epoch: 1, sessions: make(map[string]memorySession),
+		references: make(map[string]memoryReference), reports: make(map[string]memoryReport),
 	}, nil
 }
 
-func (store *MemoryStore) ReplaceSession(ctx context.Context, session Session, ttl time.Duration) error {
-	if ctx == nil || store == nil || !validSession(session) || ttl <= 0 {
+func (store *MemoryStore) CurrentOwnershipEpoch(ctx context.Context) (uint64, error) {
+	if ctx == nil || store == nil {
+		return 0, ErrInvalidStore
+	}
+	if err := ctx.Err(); err != nil {
+		return 0, err
+	}
+	store.mu.Lock()
+	defer store.mu.Unlock()
+	if store.epoch == 0 {
+		return 0, ErrInvalidStore
+	}
+	return store.epoch, nil
+}
+
+// OpenSession always replaces the previous Worker session and clears Runtime.
+func (store *MemoryStore) OpenSession(ctx context.Context, session Session, ttl time.Duration) error {
+	if ctx == nil || store == nil || ttl <= 0 {
 		return ErrInvalidSession
 	}
 	if err := ctx.Err(); err != nil {
 		return err
 	}
-	now := store.now().UTC()
-	if now.IsZero() {
-		return ErrInvalidStore
+	normalized, err := NormalizeSession(session)
+	if err != nil {
+		return err
+	}
+	now, err := store.currentTime()
+	if err != nil {
+		return err
+	}
+	store.mu.Lock()
+	defer store.mu.Unlock()
+	delete(store.reports, normalized.WorkerID)
+	store.sessions[normalized.WorkerID] = memorySession{value: normalized, expiresAt: now.Add(ttl)}
+	return nil
+}
+
+func (store *MemoryStore) RecordIssuedSnapshot(ctx context.Context, reference SnapshotReference, ttl time.Duration) error {
+	if ctx == nil || store == nil || ttl <= 0 {
+		return ErrInvalidSnapshotReference
+	}
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	normalized, err := NormalizeSnapshotReference(reference)
+	if err != nil {
+		return err
+	}
+	now, err := store.currentTime()
+	if err != nil {
+		return err
+	}
+	store.mu.Lock()
+	defer store.mu.Unlock()
+	if normalized.OwnershipEpoch != store.epoch {
+		return ErrSnapshotMismatch
+	}
+	current, exists := store.references[normalized.WorkerID]
+	if exists && !current.expiresAt.After(now) {
+		delete(store.references, normalized.WorkerID)
+		exists = false
+	}
+	if exists {
+		switch compareSnapshotTuple(normalized, current.value) {
+		case -1:
+			return ErrStaleSnapshotReference
+		case 0:
+			if normalized.Checksum != current.value.Checksum {
+				return ErrConflictingSnapshotReference
+			}
+		}
+	}
+	store.references[normalized.WorkerID] = memoryReference{value: normalized, expiresAt: now.Add(ttl)}
+	return nil
+}
+
+func (store *MemoryStore) AcknowledgeSnapshot(ctx context.Context, acknowledgement SnapshotAcknowledgement, ttl time.Duration) error {
+	if ctx == nil || store == nil || ttl <= 0 {
+		return ErrInvalidAcknowledgement
+	}
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	normalized, err := NormalizeAcknowledgement(acknowledgement)
+	if err != nil {
+		return err
+	}
+	now, err := store.currentTime()
+	if err != nil {
+		return err
+	}
+	store.mu.Lock()
+	defer store.mu.Unlock()
+	session, exists := store.sessions[normalized.WorkerID]
+	if !exists || !session.expiresAt.After(now) || session.value.SessionID != normalized.SessionID {
+		return ErrStaleSession
+	}
+	if session.value.AckedSnapshotVersion != 0 {
+		acknowledged := sessionReference(session.value)
+		switch compareSnapshotTuple(normalized.Reference, acknowledged) {
+		case -1:
+			return ErrStaleAcknowledgement
+		case 0:
+			if normalized.Reference.Checksum != acknowledged.Checksum {
+				return ErrSnapshotMismatch
+			}
+		}
+	}
+	reference, exists := store.references[normalized.WorkerID]
+	if !exists || !reference.expiresAt.After(now) {
+		return ErrSnapshotMismatch
+	}
+	switch compareSnapshotTuple(normalized.Reference, reference.value) {
+	case -1:
+		return ErrStaleAcknowledgement
+	case 1:
+		return ErrSnapshotMismatch
+	}
+	if normalized.Reference.Checksum != reference.value.Checksum {
+		return ErrSnapshotMismatch
+	}
+	if !normalized.Applied {
+		delete(store.reports, normalized.WorkerID)
+		session.value.RuntimeEnabled = false
+		session.expiresAt = now.Add(ttl)
+		store.sessions[normalized.WorkerID] = session
+		return nil
+	}
+	if session.value.AckedSnapshotVersion != 0 && compareSnapshotTuple(normalized.Reference, sessionReference(session.value)) == 0 {
+		if !session.value.RuntimeEnabled {
+			delete(store.reports, normalized.WorkerID)
+			session.value.RuntimeEnabled = true
+		}
+		session.expiresAt = now.Add(ttl)
+		store.sessions[normalized.WorkerID] = session
+		return nil
+	}
+	delete(store.reports, normalized.WorkerID)
+	session.value.AckedSnapshotVersion = normalized.Reference.Version
+	session.value.AckedOwnershipEpoch = normalized.Reference.OwnershipEpoch
+	session.value.AckedChecksum = normalized.Reference.Checksum
+	session.value.RuntimeEnabled = true
+	session.expiresAt = now.Add(ttl)
+	store.sessions[normalized.WorkerID] = session
+	return nil
+}
+
+// ReplaceSession is retained temporarily for the pre-control-plane adapters.
+func (store *MemoryStore) ReplaceSession(ctx context.Context, session Session, ttl time.Duration) error {
+	if ctx == nil || store == nil || !validLegacySession(session) || ttl <= 0 {
+		return ErrInvalidSession
+	}
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	now, err := store.currentTime()
+	if err != nil {
+		return err
 	}
 	store.mu.Lock()
 	defer store.mu.Unlock()
 	current, exists := store.sessions[session.WorkerID]
 	identityChanged := exists && (current.value.SessionID != session.SessionID || current.value.InstanceID != session.InstanceID)
 	expired := exists && !current.expiresAt.After(now)
-	if exists && !identityChanged && !expired && sessionBefore(session, current.value) {
+	if exists && !identityChanged && !expired && legacySessionBefore(session, current.value) {
 		return ErrStaleSession
 	}
-	ackAdvanced := exists && !identityChanged && !expired && sessionAfter(session, current.value)
+	ackAdvanced := exists && !identityChanged && !expired && legacySessionAfter(session, current.value)
 	if identityChanged || expired || ackAdvanced {
 		delete(store.reports, session.WorkerID)
 	}
+	session.RuntimeEnabled = true
 	store.sessions[session.WorkerID] = memorySession{value: session, expiresAt: now.Add(ttl)}
 	return nil
 }
@@ -78,44 +234,48 @@ func (store *MemoryStore) ReplaceRuntime(ctx context.Context, report Report, ttl
 	if err := ctx.Err(); err != nil {
 		return err
 	}
-	normalized, counterIndex, err := normalizeReport(report)
+	normalized, digest, err := NormalizeReport(report)
 	if err != nil {
 		return err
 	}
-	payload, err := json.Marshal(normalized)
+	now, err := store.currentTime()
 	if err != nil {
-		return ErrInvalidReport
-	}
-	digest := sha256.Sum256(payload)
-	now := store.now().UTC()
-	if now.IsZero() {
-		return ErrInvalidStore
+		return err
 	}
 	store.mu.Lock()
 	defer store.mu.Unlock()
-	session, exists := store.sessions[report.WorkerID]
-	if !exists || !session.expiresAt.After(now) || session.value.SessionID != report.SessionID {
+	session, exists := store.sessions[normalized.WorkerID]
+	if !exists || !session.expiresAt.After(now) || session.value.SessionID != normalized.SessionID {
 		return ErrStaleSession
 	}
-	if report.SnapshotVersion != session.value.AckedSnapshotVersion ||
-		report.OwnershipEpoch != session.value.AckedOwnershipEpoch {
-		return ErrStaleReport
+	if !session.value.RuntimeEnabled || normalized.SnapshotVersion != session.value.AckedSnapshotVersion ||
+		normalized.OwnershipEpoch != session.value.AckedOwnershipEpoch {
+		return ErrSnapshotMismatch
 	}
-	if current, exists := store.reports[report.WorkerID]; exists && current.value.SessionID == report.SessionID {
+	current, exists := store.reports[normalized.WorkerID]
+	if exists && !current.expiresAt.After(now) {
+		delete(store.reports, normalized.WorkerID)
+		exists = false
+	}
+	if exists && current.value.SessionID == normalized.SessionID {
 		switch {
 		case normalized.Sequence < current.value.Sequence:
 			return ErrStaleReport
 		case normalized.Sequence == current.value.Sequence && digest != current.digest:
 			return ErrConflictingReport
 		case normalized.Sequence == current.value.Sequence:
+			current.expiresAt = now.Add(ttl)
+			store.reports[normalized.WorkerID] = current
+			session.expiresAt = now.Add(ttl)
+			store.sessions[normalized.WorkerID] = session
 			return nil
 		}
 	}
-	store.reports[report.WorkerID] = memoryReport{
-		value: normalized, digest: digest, expiresAt: now.Add(ttl), counters: counterIndex,
+	store.reports[normalized.WorkerID] = memoryReport{
+		value: normalized, digest: digest, expiresAt: now.Add(ttl), counters: countersByProxy(normalized.Counters),
 	}
 	session.expiresAt = now.Add(ttl)
-	store.sessions[report.WorkerID] = session
+	store.sessions[normalized.WorkerID] = session
 	return nil
 }
 
@@ -128,7 +288,7 @@ func (store *MemoryStore) ReadRuntime(ctx context.Context, proxies []OwnedProxy)
 	}
 	seen := make(map[string]struct{}, len(proxies))
 	for _, proxy := range proxies {
-		if !clean(proxy.ProxyID) || !clean(proxy.WorkerID) || proxy.OwnershipEpoch == 0 {
+		if !ValidIdentifier(proxy.ProxyID) || !ValidIdentifier(proxy.WorkerID) || proxy.OwnershipEpoch == 0 {
 			return nil, ErrInvalidQuery
 		}
 		key := proxy.WorkerID + "\x00" + proxy.ProxyID
@@ -137,9 +297,9 @@ func (store *MemoryStore) ReadRuntime(ctx context.Context, proxies []OwnedProxy)
 		}
 		seen[key] = struct{}{}
 	}
-	now := store.now().UTC()
-	if now.IsZero() {
-		return nil, ErrInvalidStore
+	now, err := store.currentTime()
+	if err != nil {
+		return nil, err
 	}
 	store.mu.Lock()
 	defer store.mu.Unlock()
@@ -149,7 +309,7 @@ func (store *MemoryStore) ReadRuntime(ctx context.Context, proxies []OwnedProxy)
 		session, sessionExists := store.sessions[proxy.WorkerID]
 		report, reportExists := store.reports[proxy.WorkerID]
 		if !sessionExists || !reportExists || !session.expiresAt.After(now) || !report.expiresAt.After(now) ||
-			report.value.SessionID != session.value.SessionID ||
+			!session.value.RuntimeEnabled || report.value.SessionID != session.value.SessionID ||
 			report.value.SnapshotVersion != session.value.AckedSnapshotVersion ||
 			report.value.OwnershipEpoch != session.value.AckedOwnershipEpoch ||
 			report.value.OwnershipEpoch < proxy.OwnershipEpoch {
@@ -165,47 +325,31 @@ func (store *MemoryStore) ReadRuntime(ctx context.Context, proxies []OwnedProxy)
 	return result, nil
 }
 
-func normalizeReport(report Report) (Report, map[string]Counter, error) {
-	if !clean(report.WorkerID) || !clean(report.SessionID) || report.Sequence == 0 ||
-		report.SnapshotVersion == 0 || report.OwnershipEpoch == 0 || report.ObservedAt.IsZero() {
-		return Report{}, nil, ErrInvalidReport
+func (store *MemoryStore) currentTime() (time.Time, error) {
+	now := store.now().UTC()
+	if now.IsZero() {
+		return time.Time{}, ErrInvalidStore
 	}
-	normalized := report
-	normalized.ObservedAt = report.ObservedAt.UTC()
-	normalized.Counters = append([]Counter(nil), report.Counters...)
-	sort.Slice(normalized.Counters, func(left, right int) bool {
-		return normalized.Counters[left].ProxyID < normalized.Counters[right].ProxyID
-	})
-	index := make(map[string]Counter, len(normalized.Counters))
-	for _, counter := range normalized.Counters {
-		if !clean(counter.ProxyID) || counter.Active < 0 || counter.Reserved < 0 {
-			return Report{}, nil, ErrInvalidReport
-		}
-		if _, exists := index[counter.ProxyID]; exists {
-			return Report{}, nil, ErrInvalidReport
-		}
-		index[counter.ProxyID] = counter
-	}
-	return normalized, index, nil
+	return now, nil
 }
 
-func validSession(session Session) bool {
-	return clean(session.WorkerID) && clean(session.InstanceID) && clean(session.SessionID) &&
+func countersByProxy(counters []Counter) map[string]Counter {
+	indexed := make(map[string]Counter, len(counters))
+	for _, counter := range counters {
+		indexed[counter.ProxyID] = counter
+	}
+	return indexed
+}
+
+func validLegacySession(session Session) bool {
+	return ValidIdentifier(session.WorkerID) && ValidIdentifier(session.InstanceID) && ValidIdentifier(session.SessionID) &&
 		session.AckedSnapshotVersion > 0 && session.AckedOwnershipEpoch > 0
 }
 
-func sessionBefore(left, right Session) bool {
-	return left.AckedOwnershipEpoch < right.AckedOwnershipEpoch ||
-		(left.AckedOwnershipEpoch == right.AckedOwnershipEpoch &&
-			left.AckedSnapshotVersion < right.AckedSnapshotVersion)
+func legacySessionBefore(left, right Session) bool {
+	return compareSnapshotTuple(sessionReference(left), sessionReference(right)) < 0
 }
 
-func sessionAfter(left, right Session) bool {
-	return left.AckedOwnershipEpoch > right.AckedOwnershipEpoch ||
-		(left.AckedOwnershipEpoch == right.AckedOwnershipEpoch &&
-			left.AckedSnapshotVersion > right.AckedSnapshotVersion)
-}
-
-func clean(value string) bool {
-	return value != "" && strings.TrimSpace(value) == value
+func legacySessionAfter(left, right Session) bool {
+	return compareSnapshotTuple(sessionReference(left), sessionReference(right)) > 0
 }
diff --git a/internal/domain/workerruntime/memory_test.go b/internal/domain/workerruntime/memory_test.go
index 64760d4..2acbfab 100644
--- a/internal/domain/workerruntime/memory_test.go
+++ b/internal/domain/workerruntime/memory_test.go
@@ -2,11 +2,125 @@ package workerruntime
 
 import (
 	"context"
+	"crypto/sha256"
 	"errors"
 	"testing"
 	"time"
 )
 
+func TestMemoryStoreRequiresAcknowledgedSnapshotForRuntime(t *testing.T) {
+	now := time.Date(2026, 7, 31, 9, 0, 0, 0, time.UTC)
+	store := newRuntimeStore(t, &now)
+	ctx := context.Background()
+	openControlSession(t, store, "session-a", time.Minute)
+	epoch, err := store.CurrentOwnershipEpoch(ctx)
+	if err != nil {
+		t.Fatalf("CurrentOwnershipEpoch(): %v", err)
+	}
+	report := controlReport(now, "session-a", 1, 7, epoch)
+	if err := store.ReplaceRuntime(ctx, report, time.Minute); !errors.Is(err, ErrSnapshotMismatch) {
+		t.Fatalf("ReplaceRuntime(before ACK) error = %v, want ErrSnapshotMismatch", err)
+	}
+	reference := controlReference(7, epoch, "snapshot-7")
+	if err := store.RecordIssuedSnapshot(ctx, reference, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(): %v", err)
+	}
+	if err := store.AcknowledgeSnapshot(ctx, SnapshotAcknowledgement{
+		WorkerID: "worker-a", SessionID: "session-a", Reference: reference, Applied: true,
+	}, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(): %v", err)
+	}
+	if err := store.ReplaceRuntime(ctx, report, time.Minute); err != nil {
+		t.Fatalf("ReplaceRuntime(after ACK): %v", err)
+	}
+}
+
+func TestMemoryStoreNegativeAcknowledgementFencesDelayedRuntime(t *testing.T) {
+	now := time.Date(2026, 7, 31, 9, 0, 0, 0, time.UTC)
+	store := newRuntimeStore(t, &now)
+	ctx := context.Background()
+	openControlSession(t, store, "session-a", time.Minute)
+	epoch, err := store.CurrentOwnershipEpoch(ctx)
+	if err != nil {
+		t.Fatalf("CurrentOwnershipEpoch(): %v", err)
+	}
+	first := controlReference(7, epoch, "snapshot-7")
+	if err := store.RecordIssuedSnapshot(ctx, first, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(first): %v", err)
+	}
+	if err := store.AcknowledgeSnapshot(ctx, SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: first, Applied: true}, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(first): %v", err)
+	}
+	if err := store.ReplaceRuntime(ctx, controlReport(now, "session-a", 1, 7, epoch), time.Minute); err != nil {
+		t.Fatalf("ReplaceRuntime(first): %v", err)
+	}
+
+	second := controlReference(8, epoch, "snapshot-8")
+	if err := store.RecordIssuedSnapshot(ctx, second, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(second): %v", err)
+	}
+	if err := store.AcknowledgeSnapshot(ctx, SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: second, Applied: false, ErrorCode: "apply_failed"}, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(negative): %v", err)
+	}
+	if err := store.ReplaceRuntime(ctx, controlReport(now, "session-a", 2, 7, epoch), time.Minute); !errors.Is(err, ErrSnapshotMismatch) {
+		t.Fatalf("ReplaceRuntime(delayed): %v, want ErrSnapshotMismatch", err)
+	}
+	if err := store.AcknowledgeSnapshot(ctx, SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: second, Applied: true}, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(recover): %v", err)
+	}
+	if err := store.ReplaceRuntime(ctx, controlReport(now, "session-a", 2, 8, epoch), time.Minute); err != nil {
+		t.Fatalf("ReplaceRuntime(recovered): %v", err)
+	}
+}
+
+func TestMemoryStoreAcknowledgementReplayPreservesRuntimeFence(t *testing.T) {
+	now := time.Date(2026, 7, 31, 9, 0, 0, 0, time.UTC)
+	store := newRuntimeStore(t, &now)
+	ctx := context.Background()
+	openControlSession(t, store, "session-a", time.Minute)
+	epoch, err := store.CurrentOwnershipEpoch(ctx)
+	if err != nil {
+		t.Fatalf("CurrentOwnershipEpoch(): %v", err)
+	}
+	reference := controlReference(7, epoch, "snapshot-7")
+	if err := store.RecordIssuedSnapshot(ctx, reference, time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(): %v", err)
+	}
+	ack := SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: reference, Applied: true}
+	if err := store.AcknowledgeSnapshot(ctx, ack, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(first): %v", err)
+	}
+	if err := store.ReplaceRuntime(ctx, controlReport(now, "session-a", 100, 7, epoch), time.Minute); err != nil {
+		t.Fatalf("ReplaceRuntime(): %v", err)
+	}
+	if err := store.AcknowledgeSnapshot(ctx, ack, time.Minute); err != nil {
+		t.Fatalf("AcknowledgeSnapshot(replay): %v", err)
+	}
+	got, err := store.ReadRuntime(ctx, []OwnedProxy{{ProxyID: "proxy-a", WorkerID: "worker-a", OwnershipEpoch: epoch}})
+	if err != nil || len(got) != 1 || !got[0].Fresh {
+		t.Fatalf("ReadRuntime(after ACK replay) = %+v, %v", got, err)
+	}
+	if err := store.ReplaceRuntime(ctx, controlReport(now, "session-a", 99, 7, epoch), time.Minute); !errors.Is(err, ErrStaleReport) {
+		t.Fatalf("ReplaceRuntime(stale): %v, want ErrStaleReport", err)
+	}
+}
+
+func TestMemoryStoreRejectsConflictingSnapshotReference(t *testing.T) {
+	now := time.Date(2026, 7, 31, 9, 0, 0, 0, time.UTC)
+	store := newRuntimeStore(t, &now)
+	ctx := context.Background()
+	epoch, err := store.CurrentOwnershipEpoch(ctx)
+	if err != nil {
+		t.Fatalf("CurrentOwnershipEpoch(): %v", err)
+	}
+	if err := store.RecordIssuedSnapshot(ctx, controlReference(7, epoch, "first"), time.Minute); err != nil {
+		t.Fatalf("RecordIssuedSnapshot(first): %v", err)
+	}
+	if err := store.RecordIssuedSnapshot(ctx, controlReference(7, epoch, "second"), time.Minute); !errors.Is(err, ErrConflictingSnapshotReference) {
+		t.Fatalf("RecordIssuedSnapshot(conflict): %v, want ErrConflictingSnapshotReference", err)
+	}
+}
+
 func TestMemoryStoreReplacesSparseRuntimeAndClearsMissingCounters(t *testing.T) {
 	now := time.Date(2026, 7, 30, 15, 0, 0, 0, time.UTC)
 	store := newRuntimeStore(t, &now)
@@ -103,13 +217,13 @@ func TestMemoryStoreRejectsRuntimeBeyondAcknowledgedSnapshot(t *testing.T) {
 		WorkerID: "worker-a", SessionID: "session-a", Sequence: 1,
 		SnapshotVersion: 4, OwnershipEpoch: 9, ObservedAt: now,
 	}
-	if err := store.ReplaceRuntime(context.Background(), report, time.Minute); !errors.Is(err, ErrStaleReport) {
-		t.Fatalf("ReplaceRuntime(ahead snapshot) error = %v, want ErrStaleReport", err)
+	if err := store.ReplaceRuntime(context.Background(), report, time.Minute); !errors.Is(err, ErrSnapshotMismatch) {
+		t.Fatalf("ReplaceRuntime(ahead snapshot) error = %v, want ErrSnapshotMismatch", err)
 	}
 	report.SnapshotVersion = 3
 	report.OwnershipEpoch = 10
-	if err := store.ReplaceRuntime(context.Background(), report, time.Minute); !errors.Is(err, ErrStaleReport) {
-		t.Fatalf("ReplaceRuntime(ahead epoch) error = %v, want ErrStaleReport", err)
+	if err := store.ReplaceRuntime(context.Background(), report, time.Minute); !errors.Is(err, ErrSnapshotMismatch) {
+		t.Fatalf("ReplaceRuntime(ahead epoch) error = %v, want ErrSnapshotMismatch", err)
 	}
 }
 
@@ -154,3 +268,26 @@ func registerRuntimeSession(t *testing.T, store *MemoryStore, sessionID string,
 		t.Fatalf("ReplaceSession(): %v", err)
 	}
 }
+
+func openControlSession(t *testing.T, store *MemoryStore, sessionID string, ttl time.Duration) {
+	t.Helper()
+	if err := store.OpenSession(context.Background(), Session{
+		WorkerID: "worker-a", InstanceID: "instance-a", SessionID: sessionID, Zone: "zone-a", ProtocolVersion: 1,
+		Labels: map[string]string{"region": "test"},
+	}, ttl); err != nil {
+		t.Fatalf("OpenSession(): %v", err)
+	}
+}
+
+func controlReference(version, epoch uint64, content string) SnapshotReference {
+	return SnapshotReference{
+		WorkerID: "worker-a", Version: version, OwnershipEpoch: epoch, Checksum: sha256.Sum256([]byte(content)),
+	}
+}
+
+func controlReport(now time.Time, sessionID string, sequence, version, epoch uint64) Report {
+	return Report{
+		WorkerID: "worker-a", SessionID: sessionID, Sequence: sequence, SnapshotVersion: version,
+		OwnershipEpoch: epoch, ObservedAt: now, Counters: []Counter{{ProxyID: "proxy-a", Active: 1}},
+	}
+}
diff --git a/internal/domain/workerruntime/runtime.go b/internal/domain/workerruntime/runtime.go
index f4861ef..a7e423b 100644
--- a/internal/domain/workerruntime/runtime.go
+++ b/internal/domain/workerruntime/runtime.go
@@ -2,26 +2,53 @@ package workerruntime
 
 import (
 	"context"
+	"crypto/sha256"
 	"errors"
 	"time"
 )
 
 var (
-	ErrInvalidStore      = errors.New("invalid worker runtime store")
-	ErrInvalidSession    = errors.New("invalid worker runtime session")
-	ErrInvalidReport     = errors.New("invalid worker runtime report")
-	ErrInvalidQuery      = errors.New("invalid worker runtime query")
-	ErrStaleSession      = errors.New("stale worker runtime session")
-	ErrStaleReport       = errors.New("stale worker runtime report")
-	ErrConflictingReport = errors.New("conflicting worker runtime report")
+	ErrInvalidStore                 = errors.New("invalid worker runtime store")
+	ErrInvalidSession               = errors.New("invalid worker runtime session")
+	ErrInvalidReport                = errors.New("invalid worker runtime report")
+	ErrInvalidQuery                 = errors.New("invalid worker runtime query")
+	ErrStaleSession                 = errors.New("stale worker runtime session")
+	ErrStaleReport                  = errors.New("stale worker runtime report")
+	ErrConflictingReport            = errors.New("conflicting worker runtime report")
+	ErrInvalidSnapshotReference     = errors.New("invalid worker snapshot reference")
+	ErrInvalidAcknowledgement       = errors.New("invalid worker snapshot acknowledgement")
+	ErrSnapshotMismatch             = errors.New("worker snapshot does not match acknowledged state")
+	ErrStaleSnapshotReference       = errors.New("stale worker snapshot reference")
+	ErrConflictingSnapshotReference = errors.New("conflicting worker snapshot reference")
+	ErrStaleAcknowledgement         = errors.New("stale worker snapshot acknowledgement")
 )
 
 type Session struct {
 	WorkerID             string
 	InstanceID           string
 	SessionID            string
+	Zone                 string
+	ProtocolVersion      uint32
+	Labels               map[string]string
 	AckedSnapshotVersion uint64
 	AckedOwnershipEpoch  uint64
+	AckedChecksum        [sha256.Size]byte
+	RuntimeEnabled       bool
+}
+
+type SnapshotReference struct {
+	WorkerID       string
+	Version        uint64
+	OwnershipEpoch uint64
+	Checksum       [sha256.Size]byte
+}
+
+type SnapshotAcknowledgement struct {
+	WorkerID  string
+	SessionID string
+	Reference SnapshotReference
+	Applied   bool
+	ErrorCode string
 }
 
 type Counter struct {
@@ -61,6 +88,14 @@ type SessionWriter interface {
 	ReplaceSession(context.Context, Session, time.Duration) error
 }
 
+type ControlStore interface {
+	CurrentOwnershipEpoch(context.Context) (uint64, error)
+	OpenSession(context.Context, Session, time.Duration) error
+	RecordIssuedSnapshot(context.Context, SnapshotReference, time.Duration) error
+	AcknowledgeSnapshot(context.Context, SnapshotAcknowledgement, time.Duration) error
+	ReplaceRuntime(context.Context, Report, time.Duration) error
+}
+
 type ReportWriter interface {
 	ReplaceRuntime(context.Context, Report, time.Duration) error
 }
diff --git a/internal/domain/workerruntime/validation.go b/internal/domain/workerruntime/validation.go
new file mode 100644
index 0000000..0ea62b6
--- /dev/null
+++ b/internal/domain/workerruntime/validation.go
@@ -0,0 +1,138 @@
+package workerruntime
+
+import (
+	"crypto/sha256"
+	"encoding/json"
+	"regexp"
+	"sort"
+	"strings"
+)
+
+const (
+	maximumLabels          = 32
+	maximumLabelKeyBytes   = 64
+	maximumLabelValueBytes = 256
+	maximumLabelTotalBytes = 4 << 10
+)
+
+var identifierPattern = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._:-]{0,127}$`)
+
+// ValidIdentifier accepts stable Worker, Session and Proxy identifiers.
+func ValidIdentifier(value string) bool {
+	return identifierPattern.MatchString(value)
+}
+
+// NormalizeLabels validates and deep-copies the bounded Worker label set.
+func NormalizeLabels(labels map[string]string) (map[string]string, error) {
+	if len(labels) > maximumLabels {
+		return nil, ErrInvalidSession
+	}
+	normalized := make(map[string]string, len(labels))
+	total := 0
+	for key, value := range labels {
+		if !ValidIdentifier(key) || len(key) > maximumLabelKeyBytes || value == "" ||
+			strings.TrimSpace(value) != value || strings.IndexByte(value, 0) >= 0 ||
+			len(value) > maximumLabelValueBytes {
+			return nil, ErrInvalidSession
+		}
+		total += len(key) + len(value)
+		if total > maximumLabelTotalBytes {
+			return nil, ErrInvalidSession
+		}
+		normalized[key] = value
+	}
+	return normalized, nil
+}
+
+// NormalizeSession prepares a new, not-yet-acknowledged session for storage.
+func NormalizeSession(session Session) (Session, error) {
+	if !ValidIdentifier(session.WorkerID) || !ValidIdentifier(session.InstanceID) ||
+		!ValidIdentifier(session.SessionID) || !ValidIdentifier(session.Zone) ||
+		session.ProtocolVersion == 0 || session.AckedSnapshotVersion != 0 ||
+		session.AckedOwnershipEpoch != 0 || !checksumIsZero(session.AckedChecksum) ||
+		session.RuntimeEnabled {
+		return Session{}, ErrInvalidSession
+	}
+	labels, err := NormalizeLabels(session.Labels)
+	if err != nil {
+		return Session{}, err
+	}
+	session.Labels = labels
+	return session, nil
+}
+
+func NormalizeSnapshotReference(reference SnapshotReference) (SnapshotReference, error) {
+	if !ValidIdentifier(reference.WorkerID) || reference.Version == 0 || reference.OwnershipEpoch == 0 ||
+		checksumIsZero(reference.Checksum) {
+		return SnapshotReference{}, ErrInvalidSnapshotReference
+	}
+	return reference, nil
+}
+
+func NormalizeAcknowledgement(acknowledgement SnapshotAcknowledgement) (SnapshotAcknowledgement, error) {
+	if !ValidIdentifier(acknowledgement.WorkerID) || !ValidIdentifier(acknowledgement.SessionID) ||
+		(acknowledgement.ErrorCode != "" && !ValidIdentifier(acknowledgement.ErrorCode)) {
+		return SnapshotAcknowledgement{}, ErrInvalidAcknowledgement
+	}
+	reference, err := NormalizeSnapshotReference(acknowledgement.Reference)
+	if err != nil || reference.WorkerID != acknowledgement.WorkerID {
+		return SnapshotAcknowledgement{}, ErrInvalidAcknowledgement
+	}
+	acknowledgement.Reference = reference
+	return acknowledgement, nil
+}
+
+// NormalizeReport returns the canonical sparse replacement and its digest.
+func NormalizeReport(report Report) (Report, [sha256.Size]byte, error) {
+	if !ValidIdentifier(report.WorkerID) || !ValidIdentifier(report.SessionID) || report.Sequence == 0 ||
+		report.SnapshotVersion == 0 || report.OwnershipEpoch == 0 || report.ObservedAt.IsZero() {
+		return Report{}, [sha256.Size]byte{}, ErrInvalidReport
+	}
+	normalized := report
+	normalized.ObservedAt = report.ObservedAt.UTC()
+	normalized.Counters = append([]Counter(nil), report.Counters...)
+	sort.Slice(normalized.Counters, func(left, right int) bool {
+		return normalized.Counters[left].ProxyID < normalized.Counters[right].ProxyID
+	})
+	seen := make(map[string]struct{}, len(normalized.Counters))
+	for _, counter := range normalized.Counters {
+		if !ValidIdentifier(counter.ProxyID) || counter.Active < 0 || counter.Reserved < 0 {
+			return Report{}, [sha256.Size]byte{}, ErrInvalidReport
+		}
+		if _, exists := seen[counter.ProxyID]; exists {
+			return Report{}, [sha256.Size]byte{}, ErrInvalidReport
+		}
+		seen[counter.ProxyID] = struct{}{}
+	}
+	payload, err := json.Marshal(normalized)
+	if err != nil {
+		return Report{}, [sha256.Size]byte{}, ErrInvalidReport
+	}
+	return normalized, sha256.Sum256(payload), nil
+}
+
+func checksumIsZero(checksum [sha256.Size]byte) bool {
+	return checksum == [sha256.Size]byte{}
+}
+
+func compareSnapshotTuple(left, right SnapshotReference) int {
+	switch {
+	case left.OwnershipEpoch < right.OwnershipEpoch:
+		return -1
+	case left.OwnershipEpoch > right.OwnershipEpoch:
+		return 1
+	case left.Version < right.Version:
+		return -1
+	case left.Version > right.Version:
+		return 1
+	default:
+		return 0
+	}
+}
+
+func sessionReference(session Session) SnapshotReference {
+	return SnapshotReference{
+		WorkerID: session.WorkerID, Version: session.AckedSnapshotVersion,
+		OwnershipEpoch: session.AckedOwnershipEpoch, Checksum: session.AckedChecksum,
+	}
+}
diff --git a/internal/domain/workerruntime/validation_test.go b/internal/domain/workerruntime/validation_test.go
new file mode 100644
index 0000000..0f30a39
--- /dev/null
+++ b/internal/domain/workerruntime/validation_test.go
@@ -0,0 +1,63 @@
+package workerruntime
+
+import (
+	"crypto/sha256"
+	"errors"
+	"testing"
+	"time"
+)
+
+func TestNormalizeLabelsClonesAndBoundsValues(t *testing.T) {
+	source := map[string]string{"region": "cn-north"}
+	labels, err := NormalizeLabels(source)
+	if err != nil {
+		t.Fatalf("NormalizeLabels(): %v", err)
+	}
+	labels["region"] = "changed"
+	if source["region"] != "cn-north" {
+		t.Fatal("NormalizeLabels() aliases the source map")
+	}
+	if !ValidIdentifier("worker-a:1") || ValidIdentifier("worker a") || ValidIdentifier("") {
+		t.Fatal("ValidIdentifier() accepted or rejected an invalid value")
+	}
+	if _, err := NormalizeLabels(map[string]string{" region": "cn"}); !errors.Is(err, ErrInvalidSession) {
+		t.Fatalf("NormalizeLabels(invalid key) error = %v", err)
+	}
+}
+
+func TestNormalizeReportUsesStableCounterOrdering(t *testing.T) {
+	now := time.Date(2026, 7, 31, 9, 0, 0, 0, time.FixedZone("UTC+8", 8*60*60))
+	base := Report{
+		WorkerID: "worker-a", SessionID: "session-a", Sequence: 1, SnapshotVersion: 7, OwnershipEpoch: 3,
+		ObservedAt: now, Counters: []Counter{{ProxyID: "proxy-b", Active: 2}, {ProxyID: "proxy-a", Reserved: 1}},
+	}
+	normalized, digest, err := NormalizeReport(base)
+	if err != nil || normalized.ObservedAt.Location() != time.UTC || normalized.Counters[0].ProxyID != "proxy-a" {
+		t.Fatalf("NormalizeReport() = %+v, %x, %v", normalized, digest, err)
+	}
+	base.Counters[0], base.Counters[1] = base.Counters[1], base.Counters[0]
+	_, replayDigest, err := NormalizeReport(base)
+	if err != nil || digest != replayDigest {
+		t.Fatalf("NormalizeReport(reordered) digest = %x, %v; want %x", replayDigest, err, digest)
+	}
+	if _, _, err := NormalizeReport(Report{}); !errors.Is(err, ErrInvalidReport) {
+		t.Fatalf("NormalizeReport(invalid) error = %v", err)
+	}
+}
+
+func TestNormalizeSnapshotReferenceAndAcknowledgement(t *testing.T) {
+	reference := SnapshotReference{
+		WorkerID: "worker-a", Version: 7, OwnershipEpoch: 3, Checksum: sha256.Sum256([]byte("snapshot")),
+	}
+	if _, err := NormalizeSnapshotReference(reference); err != nil {
+		t.Fatalf("NormalizeSnapshotReference(): %v", err)
+	}
+	acknowledgement := SnapshotAcknowledgement{WorkerID: "worker-a", SessionID: "session-a", Reference: reference, ErrorCode: "apply_failed"}
+	if _, err := NormalizeAcknowledgement(acknowledgement); err != nil {
+		t.Fatalf("NormalizeAcknowledgement(): %v", err)
+	}
+	acknowledgement.Reference.WorkerID = "worker-b"
+	if _, err := NormalizeAcknowledgement(acknowledgement); !errors.Is(err, ErrInvalidAcknowledgement) {
+		t.Fatalf("NormalizeAcknowledgement(worker mismatch) error = %v", err)
+	}
+}