diff --git a/apps/backend/cmd/mock-agent/background_test.go b/apps/backend/cmd/mock-agent/background_test.go
index c2d29b007e..5a37cbce68 100644
--- a/apps/backend/cmd/mock-agent/background_test.go
+++ b/apps/backend/cmd/mock-agent/background_test.go
@@ -103,3 +103,25 @@ func TestAsyncSubagentForegroundFramesMatchClaudeOrdering(t *testing.T) {
 		t.Fatalf("fifth update must be final same-prompt assistant output, got %#v", got[4])
 	}
 }
+
+func TestBackgroundWorkEmitsForegroundIdleBoundary(t *testing.T) {
+	e, updates := newTestEmitter()
+	emitBackgroundWork(e, "/background 1ms")
+
+	got := updates.getUpdates()
+	idleIndex := -1
+	for i, update := range got {
+		usage := update.notification.Update.UsageUpdate
+		if usage == nil {
+			continue
+		}
+		origin := usage.Meta[claudeOriginMetaKey].(map[string]any)
+		if origin["kind"] == claudeOriginHuman {
+			idleIndex = i
+			break
+		}
+	}
+	if idleIndex < 0 {
+		t.Fatal("/background must emit a human-origin foreground-idle boundary")
+	}
+}
diff --git a/apps/backend/cmd/mock-agent/handler.go b/apps/backend/cmd/mock-agent/handler.go
index 6f113c33bb..b3aac71cba 100644
--- a/apps/backend/cmd/mock-agent/handler.go
+++ b/apps/backend/cmd/mock-agent/handler.go
@@ -381,6 +381,7 @@ func emitBackgroundWork(e *emitter, cmd string) {
 		"Background exploration",
 		"Explore the codebase while the foreground stays idle",
 		"general-purpose")
+	e.foregroundIdle()
 
 	// Hold the turn open with NO foreground output so the session stays in the
 	// background-idle substate for the whole window.
diff --git a/apps/backend/internal/backendapp/orchestrator.go b/apps/backend/internal/backendapp/orchestrator.go
index 9da8aa7b1b..92d4b3e36d 100644
--- a/apps/backend/internal/backendapp/orchestrator.go
+++ b/apps/backend/internal/backendapp/orchestrator.go
@@ -72,6 +72,8 @@ func provideOrchestrator(
 	agentManagerClient := newLifecycleAdapter(lifecycleMgr, agentRegistry, log)
 
 	serviceCfg := orchestrator.DefaultServiceConfig()
+	serviceCfg.ClaudeBackgroundPromptHandoff =
+		cfg != nil && cfg.Features.ClaudeBackgroundPromptHandoff
 	namespace := resolveEventNamespace(cfg)
 	serviceCfg.QueueGroup = "orchestrator." + namespace
 	busMode := "memory"
diff --git a/apps/backend/internal/common/config/config.go b/apps/backend/internal/common/config/config.go
index 14c7e8b35e..c484cf1347 100644
--- a/apps/backend/internal/common/config/config.go
+++ b/apps/backend/internal/common/config/config.go
@@ -397,6 +397,12 @@ type FeaturesConfig struct {
 	// Toggles). Off by default so kandev stays single-user until a deployment
 	// opts in.
 	Auth bool `mapstructure:"auth" json:"auth"`
+
+	// ClaudeBackgroundPromptHandoff gates the high-risk experiment that lets a
+	// claude-acp session accept a successor prompt after an adapter-attested
+	// foreground handoff while background work remains live. It is off in every
+	// embedded profile and must fail closed for every other provider.
+	ClaudeBackgroundPromptHandoff bool `mapstructure:"claude_background_prompt_handoff" json:"claudeBackgroundPromptHandoff"`
 }
 
 // LoggingConfig holds logging configuration.
diff --git a/apps/backend/internal/common/config/config_test.go b/apps/backend/internal/common/config/config_test.go
index 29c8a7cb4e..870c8ee6a3 100644
--- a/apps/backend/internal/common/config/config_test.go
+++ b/apps/backend/internal/common/config/config_test.go
@@ -228,6 +228,18 @@ func TestFeatures_PluginsEnabledByEnv(t *testing.T) {
 	}
 }
 
+func TestFeatures_ClaudeBackgroundPromptHandoffEnabledByEnv(t *testing.T) {
+	t.Setenv("KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF", "true")
+
+	cfg, err := LoadWithPath(t.TempDir())
+	if err != nil {
+		t.Fatalf("LoadWithPath: %v", err)
+	}
+	if !cfg.Features.ClaudeBackgroundPromptHandoff {
+		t.Error("Features.ClaudeBackgroundPromptHandoff = false, want true")
+	}
+}
+
 func TestFeatures_AppStatusBarDisabledByEnv(t *testing.T) {
 	t.Setenv("KANDEV_FEATURES_APP_STATUS_BAR", "false")
 
@@ -422,13 +434,18 @@ func TestServerHostsFromConfigWhenHostUnset(t *testing.T) {
 // without a tag) would surface as a capitalized JSON key and break the
 // frontend's case-sensitive read in apps/web/app/actions/features.ts.
 func TestFeaturesConfig_JSONShape(t *testing.T) {
-	cfg := FeaturesConfig{Office: true, Plugins: true, AppStatusBar: true, Auth: true}
+	cfg := FeaturesConfig{
+		Office:       true,
+		Plugins:      true,
+		AppStatusBar: true,
+		Auth:         true,
+	}
 	raw, err := json.Marshal(cfg)
 	if err != nil {
 		t.Fatalf("json.Marshal: %v", err)
 	}
 	got := string(raw)
-	want := `{"office":true,"plugins":true,"appStatusBar":true,"auth":true}`
+	want := `{"office":true,"plugins":true,"appStatusBar":true,"auth":true,"claudeBackgroundPromptHandoff":false}`
 	if got != want {
 		t.Errorf("FeaturesConfig JSON = %s; want %s — missing or wrong `json:` struct tag", got, want)
 	}
diff --git a/apps/backend/internal/orchestrator/background_work_accounting_test.go b/apps/backend/internal/orchestrator/background_work_accounting_test.go
index b81a85053e..57ef8b8598 100644
--- a/apps/backend/internal/orchestrator/background_work_accounting_test.go
+++ b/apps/backend/internal/orchestrator/background_work_accounting_test.go
@@ -33,7 +33,7 @@ func (b *blockingRetirementEventBus) Publish(
 ) error {
 	if subject == eventtypes.TaskSessionActivityChanged {
 		data, _ := event.Data.(map[string]interface{})
-		if value, present := data["foreground_activity"]; present && value == nil {
+		if count, present := data["active_subagent_count"]; present && count == 0 {
 			b.once.Do(func() { close(b.retirementEntered) })
 			<-b.releaseRetirement
 		}
@@ -99,7 +99,7 @@ func TestActiveSubagentCount_DerivesOnlyLiveSubagentRegistrations(t *testing.T)
 	}
 }
 
-func TestBackgroundCompletion_IntermediateSubagentPublishesBackground(t *testing.T) {
+func TestBackgroundCompletion_IntermediateSubagentPublishesGenerating(t *testing.T) {
 	repo := setupTestRepo(t)
 	const taskID, sessionID, executionID = "task-intermediate", "session-intermediate", "execution-intermediate"
 	seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateRunning)
@@ -126,14 +126,86 @@ func TestBackgroundCompletion_IntermediateSubagentPublishesBackground(t *testing
 		t.Fatalf("published events = %d, want 1", len(recorded.events))
 	}
 	data, _ := recorded.events[0].event.Data.(map[string]interface{})
-	if got := data["foreground_activity"]; got != string(v1.ForegroundActivityBackground) {
-		t.Fatalf("published foreground activity = %#v, want background", got)
+	if got := data["foreground_activity"]; got != string(v1.ForegroundActivityGenerating) {
+		t.Fatalf("published foreground activity = %#v, want generating", got)
 	}
 	if got := data["active_subagent_count"]; got != 1 {
 		t.Fatalf("published active subagent count = %#v, want 1", got)
 	}
 }
 
+func TestBackgroundCompletion_SettledSessionClearsActivityForCountOnlyUpdate(t *testing.T) {
+	repo := setupTestRepo(t)
+	const taskID, sessionID, executionID = "task-settled-intermediate", "session-settled-intermediate", "execution-settled-intermediate"
+	seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateWaitingForInput)
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+	recorded := &recordingEventBus{}
+	svc.eventBus = recorded
+	svc.registerBackgroundWorkKind(
+		sessionID, "tool-one", executionID, "child-one", streams.BackgroundWorkKindSubagent,
+	)
+	svc.registerBackgroundWorkKind(
+		sessionID, "tool-two", executionID, "child-two", streams.BackgroundWorkKindSubagent,
+	)
+	svc.markForegroundIdle(sessionID)
+
+	publication, changed := svc.completeBackgroundWorkSnapshot(
+		sessionID, executionID, "child-one", string(v1.ForegroundActivityBackground),
+	)
+	if !changed {
+		t.Fatal("intermediate settled completion must publish the count-only transition")
+	}
+	svc.publishForegroundActivitySnapshot(t.Context(), taskID, sessionID, publication)
+
+	if len(recorded.events) != 1 {
+		t.Fatalf("published events = %d, want 1", len(recorded.events))
+	}
+	data, _ := recorded.events[0].event.Data.(map[string]interface{})
+	if got := data["foreground_activity"]; got != nil {
+		t.Fatalf("settled session activity = %#v, want nil", got)
+	}
+	if got := data["active_subagent_count"]; got != 1 {
+		t.Fatalf("settled session active subagent count = %#v, want 1", got)
+	}
+}
+
+func TestBackgroundCompletion_EnabledClaudeSettledSessionPublishesBackground(t *testing.T) {
+	repo := setupTestRepo(t)
+	const taskID, sessionID, executionID = "task-settled-claude", "session-settled-claude", "execution-settled-claude"
+	seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateWaitingForInput)
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+	enableClaudeBackgroundPromptHandoffForTest(t, svc)
+	setSessionAgentNameForTest(t, svc, sessionID, "claude-acp")
+	recorded := &recordingEventBus{}
+	svc.eventBus = recorded
+	svc.registerBackgroundWorkKind(
+		sessionID, "tool-one", executionID, "child-one", streams.BackgroundWorkKindSubagent,
+	)
+	svc.registerBackgroundWorkKind(
+		sessionID, "tool-two", executionID, "child-two", streams.BackgroundWorkKindSubagent,
+	)
+	svc.markForegroundIdle(sessionID)
+
+	publication, changed := svc.completeBackgroundWorkSnapshot(
+		sessionID, executionID, "child-one", string(v1.ForegroundActivityBackground),
+	)
+	if !changed {
+		t.Fatal("intermediate enabled Claude completion must publish the count-only transition")
+	}
+	svc.publishForegroundActivitySnapshot(t.Context(), taskID, sessionID, publication)
+
+	if len(recorded.events) != 1 {
+		t.Fatalf("published events = %d, want 1", len(recorded.events))
+	}
+	data, _ := recorded.events[0].event.Data.(map[string]interface{})
+	if got := data["foreground_activity"]; got != string(v1.ForegroundActivityBackground) {
+		t.Fatalf("enabled Claude settled activity = %#v, want background", got)
+	}
+	if got := data["active_subagent_count"]; got != 1 {
+		t.Fatalf("enabled Claude settled active subagent count = %#v, want 1", got)
+	}
+}
+
 func TestBackgroundCompletion_IdentifiedRetiresExactWorkAndDuplicateIsHarmless(t *testing.T) {
 	svc := createTestService(setupTestRepo(t), newMockStepGetter(), newMockTaskRepo())
 	const taskID, sessionID, executionID = "task-accounting", "session-accounting", "execution-accounting"
@@ -201,7 +273,7 @@ func TestBackgroundCompletion_UnidentifiedRetiresOldestOfMultipleWorkloadsFIFO(t
 	if !svc.hasBackgroundTask(sessionID, "tool-two") {
 		t.Fatal("unidentified completion must leave the remaining workload live")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("completion with a live remainder changed visible activity to %q", got)
 	}
 }
@@ -241,7 +313,7 @@ func TestBackgroundCompletion_TwoUnidentifiedCompletionsRetireBothWorkloadsFIFO(
 	if !svc.hasBackgroundTask(sessionID, "tool-second") {
 		t.Fatal("first ID-less completion retired the second-registered workload out of FIFO order")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("session left background-idle with a live remainder, got %q", got)
 	}
 
@@ -251,7 +323,7 @@ func TestBackgroundCompletion_TwoUnidentifiedCompletionsRetireBothWorkloadsFIFO(
 	if svc.hasBackgroundTask(sessionID, "tool-second") {
 		t.Fatal("second ID-less completion did not retire the last remaining workload")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("session did not leave background after final completion, got %q", got)
 	}
 }
@@ -279,18 +351,18 @@ func TestBackgroundCompletion_UnidentifiedSuccessorCycleRetiresSoleSessionWork(t
 		t.Fatal("ID-less successor-cycle notification did not retire sole session workload")
 	}
 
-	activityClears := 0
+	activityUpdates := 0
 	for _, record := range recorded.events {
 		if record.subject != eventtypes.TaskSessionActivityChanged {
 			continue
 		}
 		data, _ := record.event.Data.(map[string]interface{})
-		if value, present := data["foreground_activity"]; present && value == nil {
-			activityClears++
+		if count, present := data["active_subagent_count"]; present && count == 0 {
+			activityUpdates++
 		}
 	}
-	if activityClears != 1 || len(taskEvents.activityTaskIDs) != 2 {
-		t.Fatalf("sole completion clear cardinality: session=%d task=%v", activityClears, taskEvents.activityTaskIDs)
+	if activityUpdates != 1 || len(taskEvents.activityTaskIDs) != 2 {
+		t.Fatalf("sole completion update cardinality: session=%d task=%v", activityUpdates, taskEvents.activityTaskIDs)
 	}
 
 	// The same ID-less notification re-delivered after retirement is a no-op.
@@ -385,7 +457,7 @@ func TestExecutionTeardown_StaleToolOwnershipIsNotVisibleToReusedSuccessorID(t *
 		},
 	})
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("stale predecessor tool ownership changed successor activity to %q", got)
 	}
 }
@@ -477,7 +549,7 @@ func TestExecutionStop_RetiresOnlyOwnedBackgroundWorkAndPublishesFinalTransition
 	); got != toolOwnershipChild {
 		t.Fatalf("successor tool ownership = %d, want child", got)
 	}
-	if got := svc.ForegroundActivity("session-stop-accounting"); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue("session-stop-accounting"); got != v1.ForegroundActivityBackground {
 		t.Fatalf("successor background work should remain visible, got %q", got)
 	}
 
@@ -487,7 +559,7 @@ func TestExecutionStop_RetiresOnlyOwnedBackgroundWorkAndPublishesFinalTransition
 	if svc.hasBackgroundTask("session-stop-accounting", "tool-new") {
 		t.Fatal("final stopped execution left its background registration behind")
 	}
-	if got := svc.ForegroundActivity("session-stop-accounting"); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue("session-stop-accounting"); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("final execution cleanup left stale background activity: %q", got)
 	}
 	if _, ok := turnActivityRecord(t, svc, "session-stop-accounting"); ok {
@@ -507,7 +579,7 @@ func TestExecutionStop_RetiresOnlyOwnedBackgroundWorkAndPublishesFinalTransition
 		activityValues = append(activityValues, data["foreground_activity"])
 		subagentCounts = append(subagentCounts, data["active_subagent_count"].(int))
 	}
-	wantValues := []interface{}{"generating", "generating", "background", nil}
+	wantValues := []interface{}{"generating", "generating", "generating", nil}
 	if !slices.Equal(activityValues, wantValues) {
 		t.Fatalf("execution cleanup activity values = %#v, want %#v", activityValues, wantValues)
 	}
@@ -596,8 +668,8 @@ func TestExecutionCleanup_DelayedPublicationCannotOverwriteSuccessorActivity(t *
 		data, _ := record.event.Data.(map[string]interface{})
 		values = append(values, data["foreground_activity"])
 	}
-	if len(values) != 1 || values[0] != string(v1.ForegroundActivityBackground) {
-		t.Fatalf("activity publications = %#v, want only successor background", values)
+	if len(values) != 1 || values[0] != nil {
+		t.Fatalf("activity publications = %#v, want only successor clear", values)
 	}
 	if len(taskEvents.activityTaskIDs) != 1 {
 		t.Fatalf("task aggregate publications = %v, want successor only", taskEvents.activityTaskIDs)
@@ -666,7 +738,10 @@ func TestExecutionCleanup_PublicationDeliveryIsOrderedAcrossRecordGenerations(t
 		values = append(values, data["foreground_activity"])
 		counts = append(counts, data["active_subagent_count"].(int))
 	}
-	want := []interface{}{nil, string(v1.ForegroundActivityBackground)}
+	want := []interface{}{
+		nil,
+		nil,
+	}
 	if !slices.Equal(values, want) {
 		t.Fatalf("cross-generation publications = %#v, want %#v", values, want)
 	}
@@ -817,8 +892,8 @@ func TestExecutionCleanup_DelayedNullCannotOverwriteClaimlessSuccessorStart(t *t
 			values = append(values, data["foreground_activity"])
 		}
 	}
-	if len(values) != 1 || values[0] != string(v1.ForegroundActivityGenerating) {
-		t.Fatalf("activity publications = %#v, want only successor generating", values)
+	if len(values) != 1 || values[0] != nil {
+		t.Fatalf("activity publications = %#v, want only successor clear", values)
 	}
 }
 
@@ -861,8 +936,8 @@ func TestBackgroundCompletion_IDLessSingletonDelayedNullCannotOverwriteSuccessor
 			values = append(values, data["foreground_activity"])
 		}
 	}
-	if len(values) != 1 || values[0] != string(v1.ForegroundActivityGenerating) {
-		t.Fatalf("activity publications = %#v, want only successor generating", values)
+	if len(values) != 1 || values[0] != nil {
+		t.Fatalf("activity publications = %#v, want only successor clear", values)
 	}
 }
 
@@ -905,10 +980,10 @@ func TestExecutionCleanup_AfterClaimlessBeginCannotCreateSuccessorNull(t *testin
 			values = append(values, data["foreground_activity"])
 		}
 	}
-	if len(values) != 1 || values[0] != string(v1.ForegroundActivityGenerating) {
-		t.Fatalf("activity publications = %#v, want only successor generating", values)
+	if len(values) != 1 || values[0] != nil {
+		t.Fatalf("activity publications = %#v, want only successor clear", values)
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("cleanup after begin displaced successor ownership: got %q", got)
 	}
 }
@@ -952,10 +1027,10 @@ func TestBackgroundCompletion_AfterClaimlessBeginCannotCreateSuccessorNull(t *te
 			values = append(values, data["foreground_activity"])
 		}
 	}
-	if len(values) != 1 || values[0] != string(v1.ForegroundActivityGenerating) {
-		t.Fatalf("activity publications = %#v, want only successor generating", values)
+	if len(values) != 1 || values[0] != nil {
+		t.Fatalf("activity publications = %#v, want only successor clear", values)
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("completion after begin displaced successor ownership: got %q", got)
 	}
 }
@@ -1026,25 +1101,29 @@ func TestStopSessionPathPublishesStateAndTeardownActivityClears(t *testing.T) {
 		TaskID: taskID, SessionID: sessionID, AgentExecutionID: executionID,
 	})
 
-	var stateClears, activityClears int
+	var stateClears, activityRetirements int
 	for _, record := range recorded.events {
 		data, ok := record.event.Data.(map[string]interface{})
 		if !ok {
 			continue
 		}
-		value, present := data["foreground_activity"]
-		if !present || value != nil {
-			continue
-		}
 		switch record.subject {
 		case eventtypes.TaskSessionStateChanged:
-			stateClears++
+			if value, present := data["foreground_activity"]; present && value == nil {
+				stateClears++
+			}
 		case eventtypes.TaskSessionActivityChanged:
-			activityClears++
+			if count, present := data["active_subagent_count"]; present && count == 0 {
+				activityRetirements++
+			}
 		}
 	}
-	if stateClears != 1 || activityClears != 1 {
-		t.Fatalf("session.stop clear cardinality: state=%d activity=%d, want 1/1", stateClears, activityClears)
+	if stateClears != 1 || activityRetirements != 1 {
+		t.Fatalf(
+			"session.stop retirement cardinality: state=%d activity=%d, want 1/1",
+			stateClears,
+			activityRetirements,
+		)
 	}
 	// Two task-aggregate recomputes: the teardown activity clear, plus the
 	// republish when the session leaves RUNNING (republishTaskActivityOnSettle),
@@ -1131,7 +1210,7 @@ func countActivityClears(recorded *recordingEventBus) int {
 			continue
 		}
 		data, _ := record.event.Data.(map[string]interface{})
-		if value, present := data["foreground_activity"]; present && value == nil {
+		if count, present := data["active_subagent_count"]; present && count == 0 {
 			clears++
 		}
 	}
@@ -1356,7 +1435,7 @@ func TestBackgroundActivity_ClaudeMetadataOnlyChildUpdateDoesNotReopenForeground
 
 	svc.registerBackgroundTask(sessionID, "async-agent")
 	svc.markForegroundIdle(sessionID)
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("precondition activity = %q, want background", got)
 	}
 
@@ -1373,7 +1452,7 @@ func TestBackgroundActivity_ClaudeMetadataOnlyChildUpdateDoesNotReopenForeground
 		},
 	})
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("metadata-only child update changed activity to %q, want background", got)
 	}
 }
@@ -1413,7 +1492,7 @@ func TestBackgroundActivity_ClaudeCachedChildUpdateDoesNotReopenForeground(t *te
 		},
 	})
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("cached child update changed activity to %q, want background", got)
 	}
 }
@@ -1435,7 +1514,7 @@ func TestBackgroundActivity_UnknownToolUpdatePreservesActivity(t *testing.T) {
 		},
 	})
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("unknown tool update changed activity to %q, want background", got)
 	}
 }
@@ -1475,7 +1554,7 @@ func TestBackgroundWork_RegisteredFromInitialToolCallIsRetiredOnExecutionTeardow
 		},
 	})
 	svc.markForegroundIdle(sessionID)
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("initial tool_call registration did not surface as background, got %q", got)
 	}
 
@@ -1486,7 +1565,7 @@ func TestBackgroundWork_RegisteredFromInitialToolCallIsRetiredOnExecutionTeardow
 	if svc.hasBackgroundTask(sessionID, "tool-initial-call") {
 		t.Fatal("execution teardown left the initial tool_call registration behind")
 	}
-	if got := svc.ForegroundActivity(sessionID); got == v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got == v1.ForegroundActivityBackground {
 		t.Fatalf("session still reports background after owning execution died, got %q", got)
 	}
 }
diff --git a/apps/backend/internal/orchestrator/event_handlers_streaming.go b/apps/backend/internal/orchestrator/event_handlers_streaming.go
index b503512a07..a3e779601e 100644
--- a/apps/backend/internal/orchestrator/event_handlers_streaming.go
+++ b/apps/backend/internal/orchestrator/event_handlers_streaming.go
@@ -456,10 +456,8 @@ func (s *Service) handleStreamingEventKind(
 // handleMessageStreamingEvent handles streaming message events for real-time text updates.
 // It creates a new message on first chunk (IsAppend=false) or appends to existing (IsAppend=true).
 func (s *Service) handleMessageStreamingEvent(ctx context.Context, payload *lifecycle.AgentStreamEventPayload) {
-	// Streamed foreground output means the agent is actively generating again,
-	// even if a background task is still outstanding — narrows the busy signal.
-	// Only genuine output flips the state: an empty/invalid frame is discarded by
-	// handleStreamingEventKind, so it must not spuriously reclose the prompt gate.
+	// Keep the private ownership estimate current for accounting. Only genuine
+	// output flips it; empty/invalid frames are discarded below.
 	if payload.Data.Text != "" && s.markForegroundGenerating(payload.SessionID, payload.ExecutionID) {
 		s.publishForegroundActivityChanged(ctx, payload.TaskID, payload.SessionID)
 	}
@@ -471,9 +469,8 @@ func (s *Service) handleMessageStreamingEvent(ctx context.Context, payload *life
 // handleThinkingStreamingEvent handles streaming thinking events for real-time reasoning updates.
 // It creates a new thinking message on first chunk (IsAppend=false) or appends to existing (IsAppend=true).
 func (s *Service) handleThinkingStreamingEvent(ctx context.Context, payload *lifecycle.AgentStreamEventPayload) {
-	// Streamed foreground reasoning means the agent is actively generating again.
-	// Only genuine output flips the state — an empty/invalid frame is discarded
-	// downstream, so it must not spuriously reclose the prompt gate.
+	// Keep the private ownership estimate current for accounting. Empty/invalid
+	// frames are discarded downstream.
 	if payload.Data.Text != "" && s.markForegroundGenerating(payload.SessionID, payload.ExecutionID) {
 		s.publishForegroundActivityChanged(ctx, payload.TaskID, payload.SessionID)
 	}
@@ -514,10 +511,8 @@ func (s *Service) handleToolUpdateEvent(ctx context.Context, payload *lifecycle.
 		s.publishForegroundActivityChanged(ctx, payload.TaskID, payload.SessionID)
 	}
 
-	// Background-work bookkeeping for the finer-grained busy signal runs
-	// regardless of message persistence — mirrors handleToolCallEvent — so a
-	// run-in-background shell or Monitor watch still drives the prompt gate even
-	// when no messageCreator is wired (tests, minimal configs).
+	// Background-work bookkeeping runs regardless of message persistence so
+	// accounting remains available even when no messageCreator is wired.
 	s.trackBackgroundToolUpdate(ctx, payload, ownership)
 
 	s.persistToolUpdateMessage(ctx, payload)
@@ -593,9 +588,9 @@ func (s *Service) persistToolUpdateMessage(ctx context.Context, payload *lifecyc
 	}
 }
 
-// trackBackgroundToolUpdate maintains the fine-grained busy signal's background
-// hold from a top-level tool_call_update: a terminal status clears the hold and
-// the first recognizable non-terminal frame registers it. Child tool calls
+// trackBackgroundToolUpdate maintains best-effort background accounting from a
+// top-level tool_call_update: a terminal status clears the hold and the first
+// recognizable non-terminal frame registers it. Child tool calls
 // (ParentToolCallID set) are a subagent's own internal work, not a new
 // background task, so they never touch the hold.
 func (s *Service) trackBackgroundToolUpdate(
@@ -1099,8 +1094,12 @@ func (s *Service) publishTaskSessionStateChanged(
 		}
 	}
 	var foregroundActivity interface{}
-	if nextState == models.TaskSessionStateRunning || nextState == models.TaskSessionStateWaitingForInput {
-		foregroundActivity = string(s.foregroundActivityValue(sessionID))
+	if nextState == models.TaskSessionStateRunning {
+		foregroundActivity = string(s.ForegroundActivity(sessionID))
+	} else if activity := s.ForegroundActivity(sessionID); activity == v1.ForegroundActivityBackground {
+		// Only the enabled Claude experiment can return background here.
+		// Preserve detached-work visibility as the coarse foreground settles.
+		foregroundActivity = string(activity)
 	}
 	eventData := map[string]interface{}{
 		metaKeyTaskID:            taskID,
@@ -1111,9 +1110,9 @@ func (s *Service) publishTaskSessionStateChanged(
 		metaKeyAgentProfileID:    agentProfileID,
 		"agent_profile_snapshot": session.AgentProfileSnapshot,
 		"is_passthrough":         session.IsPassthrough,
-		// Carry activity only while the session can own foreground/background
-		// work. Every other state gets an explicit null so partial client-store
-		// merges clear a previously-live substate during session.stop/teardown.
+		// Carry activity only while the durable session is RUNNING. Every other
+		// state gets an explicit null so partial client-store merges clear a
+		// previously-live busy signal during settlement or teardown.
 		"foreground_activity":   foregroundActivity,
 		"active_subagent_count": s.ActiveSubagentCount(sessionID),
 	}
diff --git a/apps/backend/internal/orchestrator/event_handlers_streaming_test.go b/apps/backend/internal/orchestrator/event_handlers_streaming_test.go
index 8011ebf2ac..6c996c863f 100644
--- a/apps/backend/internal/orchestrator/event_handlers_streaming_test.go
+++ b/apps/backend/internal/orchestrator/event_handlers_streaming_test.go
@@ -271,6 +271,34 @@ func TestUpdateTaskSessionStatePublishesPersistedUpdatedAt(t *testing.T) {
 	require.Equal(t, session.UpdatedAt.UTC().Format(time.RFC3339Nano), data["updated_at"])
 }
 
+func TestUpdateTaskSessionState_EnabledClaudePublishesSettledBackground(t *testing.T) {
+	ctx := context.Background()
+	repo := setupTestRepo(t)
+	seedSession(t, repo, "task-state-claude", "session-state-claude", "step1")
+	eb := &recordingEventBus{}
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+	enableClaudeBackgroundPromptHandoffForTest(t, svc)
+	setSessionAgentNameForTest(t, svc, "session-state-claude", "claude-acp")
+	svc.eventBus = eb
+	svc.registerBackgroundTask("session-state-claude", "background-1")
+	svc.markForegroundIdle("session-state-claude")
+
+	svc.updateTaskSessionState(
+		ctx,
+		"task-state-claude",
+		"session-state-claude",
+		models.TaskSessionStateWaitingForInput,
+		"",
+		false,
+	)
+
+	require.Len(t, eb.events, 1)
+	require.Equal(t, events.TaskSessionStateChanged, eb.events[0].subject)
+	data, ok := eb.events[0].event.Data.(map[string]interface{})
+	require.True(t, ok)
+	require.Equal(t, string(v1.ForegroundActivityBackground), data["foreground_activity"])
+}
+
 func TestTransitionTaskSessionStateReportsAcceptedWrite(t *testing.T) {
 	ctx := context.Background()
 	repo := setupTestRepo(t)
diff --git a/apps/backend/internal/orchestrator/foreground_activity_freshload_test.go b/apps/backend/internal/orchestrator/foreground_activity_freshload_test.go
index 60971e0102..4c8b3a029d 100644
--- a/apps/backend/internal/orchestrator/foreground_activity_freshload_test.go
+++ b/apps/backend/internal/orchestrator/foreground_activity_freshload_test.go
@@ -64,7 +64,7 @@ func TestFreshLoad_SettledSessionOmitsSubstate(t *testing.T) {
 	}
 }
 
-func TestFreshLoad_SettledSessionWithDetachedWorkSerializesBackground(t *testing.T) {
+func TestFreshLoad_SettledSessionWithDetachedWorkOmitsActivity(t *testing.T) {
 	repo := setupTestRepo(t)
 	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
 
@@ -73,15 +73,15 @@ func TestFreshLoad_SettledSessionWithDetachedWorkSerializesBackground(t *testing
 	svc.markForegroundIdle(sessionID)
 	sessionDTO := &taskdto.TaskSessionDTO{ID: sessionID, State: models.TaskSessionStateWaitingForInput}
 	taskdto.EnrichForegroundActivity(sessionDTO, svc)
-	if got := marshalField(t, sessionDTO); got != string(v1.ForegroundActivityBackground) {
-		t.Fatalf("settled detached session foreground_activity: got %q, want background", got)
+	if body := marshalDTO(t, sessionDTO); strings.Contains(body, "foreground_activity") {
+		t.Fatalf("settled detached session must omit foreground_activity, got %s", body)
 	}
 
 	taskDTO := &taskdto.TaskDTO{ID: "task-detached"}
 	sessions := []*models.TaskSession{{ID: sessionID, State: models.TaskSessionStateWaitingForInput}}
 	taskdto.EnrichTaskForegroundActivity(taskDTO, sessions, svc)
-	if got := marshalField(t, taskDTO); got != string(v1.ForegroundActivityBackground) {
-		t.Fatalf("detached task foreground_activity: got %q, want background", got)
+	if body := marshalDTO(t, taskDTO); strings.Contains(body, "foreground_activity") {
+		t.Fatalf("settled detached task must omit foreground_activity, got %s", body)
 	}
 }
 
diff --git a/apps/backend/internal/orchestrator/foreground_activity_prompt_cycle_test.go b/apps/backend/internal/orchestrator/foreground_activity_prompt_cycle_test.go
index 131a3d5461..00a76fc51b 100644
--- a/apps/backend/internal/orchestrator/foreground_activity_prompt_cycle_test.go
+++ b/apps/backend/internal/orchestrator/foreground_activity_prompt_cycle_test.go
@@ -1,6 +1,7 @@
 package orchestrator
 
 import (
+	"errors"
 	"testing"
 
 	"github.com/kandev/kandev/internal/agent/runtime/lifecycle"
@@ -71,18 +72,18 @@ func TestForegroundActivitySignal_FollowUpPromptKeepsIndependentCompletionIdenti
 	svc.completeTurnForTaskSession(t.Context(), taskID, sessionID)
 	svc.completeTurnForTaskSession(t.Context(), taskID, sessionID)
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("follow-up completion was mistaken for its predecessor: activity = %q", got)
 	}
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("follow-up left background-only session unpromptable: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("follow-up RUNNING session must remain unpromptable: %v", err)
 	}
 	got := activityValues(eb)
 	want := []string{
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
+		string(v1.ForegroundActivityGenerating),
+		string(v1.ForegroundActivityGenerating),
 	}
 	if len(got) != len(want) {
 		t.Fatalf("activity publications = %v, want exactly %v", got, want)
@@ -145,18 +146,18 @@ func TestForegroundActivitySignal_PreDispatchEventsUseCurrentPromptCycle(t *test
 	); err != nil {
 		t.Fatalf("dispatch follow-up prompt: %v", err)
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("pre-callback completion did not own the new prompt cycle: activity = %q", got)
 	}
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("detached work after pre-callback completion must be promptable: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("detached work must not make a RUNNING session promptable: %v", err)
 	}
 	got := activityValues(eb)
 	want := []string{
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
+		string(v1.ForegroundActivityGenerating),
+		string(v1.ForegroundActivityGenerating),
 	}
 	if len(got) != len(want) {
 		t.Fatalf("activity publications = %v, want exactly %v", got, want)
@@ -212,25 +213,13 @@ func TestForegroundActivitySignal_ClaimedPreDispatchCompletionReconcilesOnAccept
 				}
 			}
 
-			if _, err := svc.PromptTask(t.Context(), taskID, sessionID, "follow up", "", false, nil, false); err != nil {
-				t.Fatalf("dispatch claimed follow-up: %v", err)
+			if _, err := svc.PromptTask(
+				t.Context(), taskID, sessionID, "follow up", "", false, nil, false,
+			); !errors.Is(err, ErrAgentPromptInProgress) {
+				t.Fatalf("RUNNING session must reject claimed follow-up: %v", err)
 			}
-			got := activityValues(eb)
-			if tt.keepWork {
-				want := []string{string(v1.ForegroundActivityGenerating), string(v1.ForegroundActivityBackground)}
-				if len(got) != len(want) || got[0] != want[0] || got[1] != want[1] {
-					t.Fatalf("claimed pre-callback publications = %v, want %v", got, want)
-				}
-				if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-					t.Fatalf("accepted completed foreground with detached work must be promptable: %v", err)
-				}
-				return
-			}
-			if len(got) != 1 || got[0] != string(v1.ForegroundActivityGenerating) {
-				t.Fatalf("no-work completion publications = %v, want generating claim only", got)
-			}
-			if gotActivity := svc.ForegroundActivity(sessionID); gotActivity != v1.ForegroundActivityGenerating {
-				t.Fatalf("no-work completion must settle without background hold, got %q", gotActivity)
+			if len(activityValues(eb)) != 0 {
+				t.Fatalf("rejected follow-up must not publish an activity change: %v", activityValues(eb))
 			}
 		})
 	}
diff --git a/apps/backend/internal/orchestrator/foreground_activity_signal_test.go b/apps/backend/internal/orchestrator/foreground_activity_signal_test.go
index 170bea6581..134e4742e8 100644
--- a/apps/backend/internal/orchestrator/foreground_activity_signal_test.go
+++ b/apps/backend/internal/orchestrator/foreground_activity_signal_test.go
@@ -176,7 +176,7 @@ func TestForegroundActivitySignal_PublishesOnFlips(t *testing.T) {
 	got := activityValues(eb)
 	want := []string{
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
+		string(v1.ForegroundActivityGenerating),
 		string(v1.ForegroundActivityGenerating),
 	}
 	if len(got) != len(want) {
@@ -246,8 +246,8 @@ func TestForegroundActivitySignal_NoPublishWithoutFlip(t *testing.T) {
 	want := []string{
 		string(v1.ForegroundActivityGenerating),
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
-		string(v1.ForegroundActivityBackground),
+		string(v1.ForegroundActivityGenerating),
+		string(v1.ForegroundActivityGenerating),
 		string(v1.ForegroundActivityGenerating),
 	}
 	if len(got) != len(want) {
@@ -260,7 +260,7 @@ func TestForegroundActivitySignal_NoPublishWithoutFlip(t *testing.T) {
 	}
 }
 
-func TestForegroundActivitySignal_ClaimReleasePublishesRestoredBackground(t *testing.T) {
+func TestForegroundActivitySignal_ClaimReleasePublishesCoarseGenerating(t *testing.T) {
 	repo := setupTestRepo(t)
 	agentMgr := &mockAgentManager{}
 	svc := createTestServiceWithAgent(repo, newMockStepGetter(), newMockTaskRepo(), agentMgr)
@@ -276,17 +276,19 @@ func TestForegroundActivitySignal_ClaimReleasePublishesRestoredBackground(t *tes
 	svc.registerBackgroundTask(sessionID, "background-1")
 	svc.markForegroundIdle(sessionID)
 
-	// Admission claims the foreground, but the missing executor row makes
-	// ensureSessionRunning fail before the prompt reaches the agent. Releasing
-	// that claim must tell every client that background-idle was restored.
-	if _, err := svc.PromptTask(context.Background(), taskID, sessionID, "retry", "", false, nil, false); err == nil {
-		t.Fatal("expected prompt preflight to fail without an executor record")
+	claim := svc.claimForegroundTurn(sessionID)
+	if claim == nil {
+		t.Fatal("expected dormant tracker to allow an internal foreground claim")
+	}
+	svc.releaseForegroundClaimOnFailure(context.Background(), taskID, sessionID, claim)
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
+		t.Fatalf("released internal claim did not restore background tracking: %q", got)
 	}
 
 	got := activityValues(eb)
-	want := []string{string(v1.ForegroundActivityBackground)}
+	want := []string{string(v1.ForegroundActivityGenerating)}
 	if len(got) != len(want) || got[0] != want[0] {
-		t.Fatalf("expected restored background activity broadcast %v, got %v", want, got)
+		t.Fatalf("expected coarse generating activity broadcast %v, got %v", want, got)
 	}
 }
 
@@ -320,22 +322,19 @@ func TestForegroundActivitySignal_ModelSwitchPublishesClaimedGenerating(t *testi
 	svc.registerBackgroundTask(sessionID, "background-1")
 	svc.markForegroundIdle(sessionID)
 
-	result, err := svc.PromptTask(context.Background(), taskID, sessionID, "continue", "new-model", false, nil, false)
-	if err != nil {
-		t.Fatalf("model-switch prompt failed: %v", err)
-	}
-	if result == nil || result.StopReason != "model_switched" {
-		t.Fatalf("expected restart-based model switch result, got %#v", result)
+	if _, err := svc.PromptTask(
+		context.Background(), taskID, sessionID, "continue", "new-model", false, nil, false,
+	); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("model-switch prompt must remain blocked while RUNNING: %v", err)
 	}
 
 	got := activityValues(eb)
-	want := []string{string(v1.ForegroundActivityGenerating)}
-	if len(got) != len(want) || got[0] != want[0] {
-		t.Fatalf("expected claimed foreground activity broadcast %v, got %v", want, got)
+	if len(got) != 0 {
+		t.Fatalf("rejected model-switch prompt published activity: %v", got)
 	}
 }
 
-func TestForegroundActivitySignal_DispatchPublishesBackgroundRegisteredDuringClaim(t *testing.T) {
+func TestForegroundActivitySignal_DispatchPublishesCoarseActivity(t *testing.T) {
 	repo := setupTestRepo(t)
 	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
 	eb := &recordingEventBus{}
@@ -352,7 +351,7 @@ func TestForegroundActivitySignal_DispatchPublishesBackgroundRegisteredDuringCla
 		t.Fatal("prompt must claim the background-idle turn")
 	}
 	svc.registerBackgroundTask(sessionID, "background-2")
-	if s := svc.ForegroundActivity(sessionID); s != v1.ForegroundActivityGenerating {
+	if s := svc.foregroundActivityValue(sessionID); s != v1.ForegroundActivityGenerating {
 		t.Fatalf("active claim must remain generating, got %q", s)
 	}
 
@@ -362,12 +361,15 @@ func TestForegroundActivitySignal_DispatchPublishesBackgroundRegisteredDuringCla
 	if !svc.markForegroundIdle(sessionID) {
 		t.Fatal("foreground idle must expose work registered during admission")
 	}
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
+		t.Fatalf("precondition: private activity = %q, want background", got)
+	}
 	svc.publishForegroundActivityChanged(context.Background(), taskID, sessionID)
 
 	got := activityValues(eb)
-	want := []string{string(v1.ForegroundActivityBackground)}
+	want := []string{string(v1.ForegroundActivityGenerating)}
 	if len(got) != len(want) || got[0] != want[0] {
-		t.Fatalf("expected dispatch-time background activity broadcast %v, got %v", want, got)
+		t.Fatalf("expected coarse dispatch-time activity broadcast %v, got %v", want, got)
 	}
 }
 
@@ -436,7 +438,7 @@ func TestForegroundActivitySignal_PropagatesToTaskLevel(t *testing.T) {
 	}
 }
 
-func TestForegroundActivitySignal_TurnCompletionPublishesBackgroundExactlyOnce(t *testing.T) {
+func TestForegroundActivitySignal_TurnCompletionPublishesCoarseExactlyOnce(t *testing.T) {
 	tests := []struct {
 		name string
 		act  func(*Service, string, string)
@@ -489,9 +491,9 @@ func TestForegroundActivitySignal_TurnCompletionPublishesBackgroundExactlyOnce(t
 			tt.act(svc, taskID, sessionID)
 
 			got := activityValues(eb)
-			want := []string{string(v1.ForegroundActivityBackground)}
+			want := []string{string(v1.ForegroundActivityGenerating)}
 			if len(got) != len(want) || got[0] != want[0] {
-				t.Fatalf("expected exactly one session background publication %v, got %v", want, got)
+				t.Fatalf("expected exactly one coarse session publication %v, got %v", want, got)
 			}
 			if len(taskEvents.activityTaskIDs) != 1 || taskEvents.activityTaskIDs[0] != taskID {
 				t.Fatalf("expected exactly one task aggregate publication for %q, got %v", taskID, taskEvents.activityTaskIDs)
@@ -602,18 +604,20 @@ func TestForegroundActivitySignal_SamePromptOutputAfterIdleDoesNotInvalidateComp
 			})
 			svc.completeTurnForTaskSession(t.Context(), taskID, sessionID)
 
-			if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+			if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 				t.Fatalf("same-prompt %s made completion stale: got activity %q", tt.outputType, got)
 			}
-			if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-				t.Fatalf("background-only session must accept immediate input: %v", err)
+			if err := svc.checkSessionPromptable(
+				taskID, sessionID, models.TaskSessionStateRunning,
+			); !errors.Is(err, ErrAgentPromptInProgress) {
+				t.Fatalf("background-only RUNNING session must reject immediate input: %v", err)
 			}
 			got := activityValues(eb)
 			want := []string{
 				string(v1.ForegroundActivityGenerating),
-				string(v1.ForegroundActivityBackground),
 				string(v1.ForegroundActivityGenerating),
-				string(v1.ForegroundActivityBackground),
+				string(v1.ForegroundActivityGenerating),
+				string(v1.ForegroundActivityGenerating),
 			}
 			if len(got) != len(want) {
 				t.Fatalf("activity publications = %v, want exactly %v", got, want)
@@ -676,7 +680,7 @@ func TestForegroundActivitySignal_DetachedLaunchTerminalOutputStaysBackground(t
 		},
 	})
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("terminal launch card must not impersonate foreground output: got %q", got)
 	}
 	if !svc.hasBackgroundTask(sessionID, toolID) {
@@ -684,7 +688,7 @@ func TestForegroundActivitySignal_DetachedLaunchTerminalOutputStaysBackground(t
 	}
 	if got := activityValues(eb); !slices.Equal(got, []string{
 		string(v1.ForegroundActivityGenerating),
-		string(v1.ForegroundActivityBackground),
+		string(v1.ForegroundActivityGenerating),
 	}) {
 		t.Fatalf("detached launch activity sequence = %v", got)
 	}
@@ -716,7 +720,7 @@ func TestForegroundActivitySignal_SynchronousDispatchFailureReleasesCycleClaim(t
 	); err == nil {
 		t.Fatal("expected synchronous provider dispatch failure")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("failed dispatch must release its foreground claim, got %q", got)
 	}
 	if retryClaim := svc.claimForegroundTurn(sessionID); retryClaim == nil {
@@ -747,7 +751,7 @@ func TestForegroundActivitySignal_TurnCompletionPreservesFinalBackgroundCompleti
 	})
 
 	got := activityValues(eb)
-	want := []string{string(v1.ForegroundActivityBackground), string(v1.ForegroundActivityGenerating)}
+	want := []string{string(v1.ForegroundActivityGenerating), string(v1.ForegroundActivityGenerating)}
 	if len(got) != len(want) || got[0] != want[0] || got[1] != want[1] {
 		t.Fatalf("expected completion and final-background publications %v, got %v", want, got)
 	}
@@ -785,7 +789,7 @@ func TestForegroundActivitySignal_DelayedOldCompletionCannotYieldSuccessor(t *te
 	// has already claimed and begun generating in the same session.
 	svc.completeTurnForSession(t.Context(), sessionID)
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("delayed old completion yielded successor foreground: got %q", got)
 	}
 	if got := activityValues(eb); len(got) != 0 {
@@ -826,7 +830,7 @@ func TestForegroundActivitySignal_OldCompletionBeforeSuccessorLeavesSuccessorCom
 	// the successor is current and must expose the still-running background task.
 	svc.completeTurnForSession(t.Context(), sessionID)
 
-	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityBackground) {
+	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityGenerating) {
 		t.Fatalf("current successor completion must publish background once, got %v", got)
 	}
 	if len(taskEvents.activityTaskIDs) != 1 || taskEvents.activityTaskIDs[0] != taskID {
@@ -851,7 +855,7 @@ func TestForegroundActivitySignal_TaskLookupFailureDoesNotConsumeCompletionYield
 	svc.repo = &failOnceGetTaskSessionRepo{repoStore: baseRepo, err: errors.New("transient lookup failure")}
 
 	svc.completeTurnForSession(t.Context(), sessionID)
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("failed identity lookup must not consume transition, got %q", got)
 	}
 	if got := activityValues(eb); len(got) != 0 {
@@ -859,7 +863,7 @@ func TestForegroundActivitySignal_TaskLookupFailureDoesNotConsumeCompletionYield
 	}
 
 	svc.completeTurnForSession(t.Context(), sessionID)
-	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityBackground) {
+	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityGenerating) {
 		t.Fatalf("retry must publish preserved background transition once, got %v", got)
 	}
 	if len(taskEvents.activityTaskIDs) != 1 || taskEvents.activityTaskIDs[0] != taskID {
@@ -888,13 +892,13 @@ func TestForegroundActivitySignal_TurnCompletionIsSessionIsolated(t *testing.T)
 
 	svc.completeTurnForSession(t.Context(), sessionA)
 
-	if got := svc.ForegroundActivity(sessionA); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionA); got != v1.ForegroundActivityBackground {
 		t.Fatalf("completed session A must become background, got %q", got)
 	}
-	if got := svc.ForegroundActivity(sessionB); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionB); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("completion for session A mutated session B: got %q", got)
 	}
-	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityBackground) {
+	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityGenerating) {
 		t.Fatalf("expected one session A background event, got %v", got)
 	}
 	if len(taskEvents.activityTaskIDs) != 1 || taskEvents.activityTaskIDs[0] != taskA {
@@ -934,7 +938,7 @@ func TestForegroundActivitySignal_SettleRepublishesTaskAggregate(t *testing.T) {
 	// left behind after retirement, whose foreground activity safely defaults to
 	// generating.
 	seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateRunning)
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("untracked RUNNING session must default generating, got %q", got)
 	}
 	taskEvents.activityTaskIDs = nil
@@ -1014,7 +1018,7 @@ func TestForegroundActivitySignal_DelayedOldProviderIdleCannotYieldSuccessor(t *
 		},
 	})
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("delayed old provider idle yielded successor foreground: got %q", got)
 	}
 	if got := activityValues(eb); len(got) != 0 {
@@ -1035,10 +1039,10 @@ func TestForegroundActivitySignal_DelayedOldProviderIdleCannotYieldSuccessor(t *
 			PromptGeneration: 2,
 		},
 	})
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("current provider idle must yield promptly, got %q", got)
 	}
-	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityBackground) {
+	if got := activityValues(eb); len(got) != 1 || got[0] != string(v1.ForegroundActivityGenerating) {
 		t.Fatalf("current provider idle must publish background once, got %v", got)
 	}
 	if len(taskEvents.activityTaskIDs) != 1 || taskEvents.activityTaskIDs[0] != taskID {
diff --git a/apps/backend/internal/orchestrator/foreground_busy_signal_test.go b/apps/backend/internal/orchestrator/foreground_busy_signal_test.go
index d87699b3a0..a0e3030a46 100644
--- a/apps/backend/internal/orchestrator/foreground_busy_signal_test.go
+++ b/apps/backend/internal/orchestrator/foreground_busy_signal_test.go
@@ -11,6 +11,30 @@ import (
 	v1 "github.com/kandev/kandev/pkg/api/v1"
 )
 
+func enableClaudeBackgroundPromptHandoffForTest(t *testing.T, svc *Service) {
+	t.Helper()
+	svc.config.ClaudeBackgroundPromptHandoff = true
+}
+
+func setSessionAgentNameForTest(
+	t *testing.T,
+	svc *Service,
+	sessionID, agentName string,
+) {
+	t.Helper()
+	session, err := svc.repo.GetTaskSession(t.Context(), sessionID)
+	if err != nil {
+		t.Fatalf("GetTaskSession(%q): %v", sessionID, err)
+	}
+	session.AgentProfileSnapshot = map[string]interface{}{
+		"agent_id":   "persisted-agent-record-id",
+		"agent_name": agentName,
+	}
+	if err := svc.repo.UpdateTaskSession(t.Context(), session); err != nil {
+		t.Fatalf("UpdateTaskSession(%q): %v", sessionID, err)
+	}
+}
+
 func emitForegroundIdle(svc *Service, taskID, sessionID string) {
 	svc.handleAgentStreamEvent(context.Background(), &lifecycle.AgentStreamEventPayload{
 		TaskID: taskID, SessionID: sessionID,
@@ -18,18 +42,11 @@ func emitForegroundIdle(svc *Service, taskID, sessionID string) {
 	})
 }
 
-// TestCheckSessionPromptable_BackgroundTaskAcceptsInput is the red
-// characterization test for ADR-0049: a session whose
-// foreground turn is idle while a spawned background task is still running must
-// accept a new message, not be rejected as "already running".
-//
-// Before the fix, checkSessionPromptable rejected ANY RUNNING session with
-// ErrAgentPromptInProgress, so an operator whose agent kicked off background
-// work was locked out of the conversation. After the fix, a RUNNING session
-// with an outstanding background task (and no active foreground generation) is
-// promptable, while a RUNNING session that is genuinely generating in the
-// foreground is still gated.
-func TestCheckSessionPromptable_BackgroundTaskAcceptsInput(t *testing.T) {
+// TestCheckSessionPromptable_BackgroundTaskRemainsBusy pins the conservative
+// admission contract from ADR-2026-07-28: provider background-work inference
+// may remain useful for accounting, but it cannot relax a RUNNING session's
+// prompt gate.
+func TestCheckSessionPromptable_BackgroundTaskRemainsBusy(t *testing.T) {
 	repo := setupTestRepo(t)
 	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
 
@@ -44,9 +61,13 @@ func TestCheckSessionPromptable_BackgroundTaskAcceptsInput(t *testing.T) {
 	svc.registerBackgroundTask(sessionID, "tool-subagent-1")
 	svc.markForegroundIdle(sessionID)
 
-	// The session must now accept a new message even though its state is RUNNING.
-	if err := svc.checkSessionPromptable("task1", sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("RUNNING session waiting only on background work must be promptable, got: %v", err)
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
+		t.Fatalf("precondition: private tracker activity = %q, want background", got)
+	}
+
+	// Background accounting must not make the RUNNING session promptable.
+	if err := svc.checkSessionPromptable("task1", sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("RUNNING session waiting on background work must remain gated, got: %v", err)
 	}
 
 	// Once the background task finishes, the (still open) turn is once again a
@@ -57,6 +78,59 @@ func TestCheckSessionPromptable_BackgroundTaskAcceptsInput(t *testing.T) {
 	}
 }
 
+func TestCheckSessionPromptable_ClaudeExperimentAcceptsBackgroundIdle(t *testing.T) {
+	repo := setupTestRepo(t)
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+	enableClaudeBackgroundPromptHandoffForTest(t, svc)
+
+	const taskID = "task-claude-experiment"
+	const sessionID = "session-claude-experiment"
+	seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateRunning)
+	setSessionAgentNameForTest(t, svc, sessionID, "claude-acp")
+
+	svc.registerBackgroundTask(sessionID, "tool-subagent-1")
+	svc.markForegroundIdle(sessionID)
+
+	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+		t.Fatalf("enabled Claude activity = %q, want background", got)
+	}
+	if err := svc.checkSessionPromptable(
+		taskID,
+		sessionID,
+		models.TaskSessionStateRunning,
+	); err != nil {
+		t.Fatalf("enabled Claude background-idle session rejected: %v", err)
+	}
+}
+
+func TestCheckSessionPromptable_ClaudeExperimentRejectsNonClaude(t *testing.T) {
+	repo := setupTestRepo(t)
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+	enableClaudeBackgroundPromptHandoffForTest(t, svc)
+
+	const taskID = "task-codex-experiment"
+	const sessionID = "session-codex-experiment"
+	seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateRunning)
+	setSessionAgentNameForTest(t, svc, sessionID, "codex-acp")
+
+	// Deliberately forge the private tracker state. Provider gating must remain
+	// a separate fail-closed boundary even if a future normalizer regression
+	// incorrectly attests a non-Claude workload.
+	svc.registerBackgroundTask(sessionID, "tool-subagent-1")
+	svc.markForegroundIdle(sessionID)
+
+	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+		t.Fatalf("enabled non-Claude activity = %q, want generating", got)
+	}
+	if err := svc.checkSessionPromptable(
+		taskID,
+		sessionID,
+		models.TaskSessionStateRunning,
+	); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("enabled non-Claude background-idle session must remain gated, got: %v", err)
+	}
+}
+
 func TestForegroundToolCallClosesBackgroundIdleGate(t *testing.T) {
 	repo := setupTestRepo(t)
 	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
@@ -82,14 +156,8 @@ func TestForegroundToolCallClosesBackgroundIdleGate(t *testing.T) {
 	}
 }
 
-// TestTurnActivity_ForegroundBackgroundTransitions locks in the state machine
-// behind isForegroundTurnGenerating.
-// TestForegroundActivity_ExportedValue covers the seam the page-load / list
-// serialization layer depends on (ADR-0049): the exported
-// ForegroundActivity mirror of the in-memory tracker. An untracked session — which
-// includes every session after a backend restart, since a restart ends the turn —
-// must report the safe "generating" default so a stale "you may type" can never be
-// serialized.
+// TestForegroundActivity_ExportedValue proves the public seam stays coarse
+// while the dormant tracker retains its fine-grained value.
 func TestForegroundActivity_ExportedValue(t *testing.T) {
 	repo := setupTestRepo(t)
 	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
@@ -105,8 +173,11 @@ func TestForegroundActivity_ExportedValue(t *testing.T) {
 		t.Fatalf("registration must not override foreground activity, got %q", got)
 	}
 	svc.markForegroundIdle(s)
-	if got := svc.ForegroundActivity(s); got != v1.ForegroundActivityBackground {
-		t.Fatalf("after foreground idle with background work, got %q, want background", got)
+	if got := svc.foregroundActivityValue(s); got != v1.ForegroundActivityBackground {
+		t.Fatalf("private activity after foreground idle = %q, want background", got)
+	}
+	if got := svc.ForegroundActivity(s); got != v1.ForegroundActivityGenerating {
+		t.Fatalf("public activity after foreground idle = %q, want generating", got)
 	}
 
 	svc.completeBackgroundTask(s, "t1")
@@ -238,9 +309,8 @@ func TestBackgroundCompleteEventRetiresOneOutstandingTask(t *testing.T) {
 }
 
 // TestForegroundBusySignal_WiredThroughStreamEvents drives the real agent
-// stream-event dispatch to prove the WS1 producer → WS2 gate wiring end to end:
-// a subagent tool_call arriving on the stream flips the promptable gate from
-// "reject (agent running)" to "accept (only background work outstanding)".
+// stream-event dispatch to prove background accounting does not relax the
+// coarse RUNNING gate.
 func TestForegroundBusySignal_WiredThroughStreamEvents(t *testing.T) {
 	repo := setupTestRepo(t)
 	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
@@ -269,9 +339,9 @@ func TestForegroundBusySignal_WiredThroughStreamEvents(t *testing.T) {
 	})
 	emitForegroundIdle(svc, taskID, sessionID)
 
-	// The gate now accepts a new message even though the session state is RUNNING.
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("after a background subagent tool_call the session must be promptable, got: %v", err)
+	// The private tracker yields, but the public gate remains closed.
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("background subagent work must not make RUNNING promptable, got: %v", err)
 	}
 
 	// A child tool_call from inside the subagent (ParentToolCallID set) is the
@@ -288,8 +358,8 @@ func TestForegroundBusySignal_WiredThroughStreamEvents(t *testing.T) {
 			Normalized:       streams.NewShellExec("ls", "", "", 0, false),
 		},
 	})
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("a subagent-internal child tool_call must not re-gate input, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("a subagent-internal child tool_call must leave RUNNING gated, got: %v", err)
 	}
 }
 
@@ -309,7 +379,7 @@ func TestForegroundBusySignal_TerminalToolUpdateReclosesGate(t *testing.T) {
 		sessionID = "session-stream"
 	)
 
-	// A top-level subagent tool_call opens the gate.
+	// A top-level subagent tool_call is tracked without opening the coarse gate.
 	svc.handleAgentStreamEvent(context.Background(), &lifecycle.AgentStreamEventPayload{
 		TaskID:    taskID,
 		SessionID: sessionID,
@@ -321,8 +391,8 @@ func TestForegroundBusySignal_TerminalToolUpdateReclosesGate(t *testing.T) {
 		},
 	})
 	emitForegroundIdle(svc, taskID, sessionID)
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("precondition: background subagent tool_call should open the gate, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("background subagent tool_call must leave RUNNING gated, got: %v", err)
 	}
 
 	// The subagent's own terminal tool_update arrives on the stream.
@@ -360,7 +430,7 @@ func TestForegroundBusySignal_TerminalToolUpdateReclosesGateByIDNotKind(t *testi
 		sessionID = "session-stream"
 	)
 
-	// A top-level subagent tool_call opens the gate.
+	// A top-level subagent tool_call is tracked without opening the coarse gate.
 	svc.handleAgentStreamEvent(context.Background(), &lifecycle.AgentStreamEventPayload{
 		TaskID:    taskID,
 		SessionID: sessionID,
@@ -372,8 +442,8 @@ func TestForegroundBusySignal_TerminalToolUpdateReclosesGateByIDNotKind(t *testi
 		},
 	})
 	emitForegroundIdle(svc, taskID, sessionID)
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("precondition: background subagent tool_call should open the gate, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("background subagent tool_call must leave RUNNING gated, got: %v", err)
 	}
 
 	// The terminal update for the SAME tool-call ID carries a plain, non-background
@@ -408,7 +478,7 @@ func TestForegroundBusySignal_UnregisteredTerminalToolUpdateLeavesGateOpen(t *te
 		sessionID = "session-stream"
 	)
 
-	// A top-level subagent tool_call opens the gate.
+	// A top-level subagent tool_call is tracked without opening the coarse gate.
 	svc.handleAgentStreamEvent(context.Background(), &lifecycle.AgentStreamEventPayload{
 		TaskID:    taskID,
 		SessionID: sessionID,
@@ -420,8 +490,8 @@ func TestForegroundBusySignal_UnregisteredTerminalToolUpdateLeavesGateOpen(t *te
 		},
 	})
 	emitForegroundIdle(svc, taskID, sessionID)
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("precondition: background subagent tool_call should open the gate, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("background subagent tool_call must leave RUNNING gated, got: %v", err)
 	}
 
 	// A terminal tool_update for an ID that was never registered as a background
@@ -437,8 +507,8 @@ func TestForegroundBusySignal_UnregisteredTerminalToolUpdateLeavesGateOpen(t *te
 		},
 	})
 
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("a terminal update for an unregistered tool-call ID must not re-gate input while background work is still outstanding, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("an unrelated terminal update must leave RUNNING gated, got: %v", err)
 	}
 }
 
@@ -539,8 +609,8 @@ func TestForegroundBusySignal_BackgroundShellViaUpdate(t *testing.T) {
 		},
 	})
 	emitForegroundIdle(svc, taskID, sessionID)
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("a run_in_background shell tool_update must open the gate, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("a background shell update must leave RUNNING gated, got: %v", err)
 	}
 
 	// Terminal update closes the launch card, not the detached workload.
@@ -554,8 +624,8 @@ func TestForegroundBusySignal_BackgroundShellViaUpdate(t *testing.T) {
 			Normalized: attestedBackgroundShellPayload("npm run dev"),
 		},
 	})
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("terminal shell launch update must preserve background promptability, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("terminal shell launch update must leave RUNNING gated, got: %v", err)
 	}
 
 	svc.handleAgentStreamEvent(context.Background(), &lifecycle.AgentStreamEventPayload{
@@ -648,8 +718,8 @@ func TestForegroundBusySignal_MonitorViaUpdate(t *testing.T) {
 		},
 	})
 	emitForegroundIdle(svc, taskID, sessionID)
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("an active Monitor registration tool_update must open the gate, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("an active Monitor update must leave RUNNING gated, got: %v", err)
 	}
 
 	// sweepMonitorsOnPromptEnd emits a terminal "complete" tool_update with the
@@ -701,8 +771,8 @@ func TestForegroundBusySignal_UpdateDoesNotReYieldAfterForeground(t *testing.T)
 	// A background run_in_background shell is recognized on its first update.
 	bgUpdate()
 	emitForegroundIdle(svc, taskID, sessionID)
-	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); err != nil {
-		t.Fatalf("precondition: background shell update should open the gate, got: %v", err)
+	if err := svc.checkSessionPromptable(taskID, sessionID, models.TaskSessionStateRunning); !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("background shell update must leave RUNNING gated, got: %v", err)
 	}
 
 	// The foreground resumes generating (streamed message chunk).
diff --git a/apps/backend/internal/orchestrator/foreground_claim_test.go b/apps/backend/internal/orchestrator/foreground_claim_test.go
index d6903e77c4..369e799fb8 100644
--- a/apps/backend/internal/orchestrator/foreground_claim_test.go
+++ b/apps/backend/internal/orchestrator/foreground_claim_test.go
@@ -12,16 +12,9 @@ import (
 	v1 "github.com/kandev/kandev/pkg/api/v1"
 )
 
-// ADR-0049 narrowed the busy gate so a RUNNING session whose foreground turn has
-// yielded to background work accepts a new prompt. checkSessionPromptable only
-// *reads* that substate, though, and PromptTask does real work between the read
-// and the point the turn is marked generating (session reload, ensureSessionRunning,
-// an optionally network-bound model switch). Two prompts arriving in that window —
-// a double-send, or two tabs on the same session — would both pass the read and
-// both reach executor.Prompt, starting overlapping turns on one ACP session.
-//
-// claimForegroundTurn closes the window: the check and the claim happen under one
-// lock, so exactly one caller wins.
+// ADR-0049 introduced tracker-side admission claims. The coarse policy no
+// longer reaches them from operator prompt admission, but the dormant mechanism
+// remains race-safe for a future protocol-backed design.
 
 // TestClaimForegroundTurn_OnlyOneConcurrentPromptWins is the regression test for
 // that race. Every claim but one must lose, no matter how many race in at once.
@@ -179,18 +172,18 @@ func TestPromptTask_ConcurrentPromptsIntoBackgroundIdleStartOneTurn(t *testing.T
 	start.Done()
 	done.Wait()
 
-	if accepted != 1 {
-		t.Fatalf("exactly one concurrent prompt may open a turn, got %d accepted (%d rejected busy)", accepted, rejectedBusy)
+	if accepted != 0 {
+		t.Fatalf("no concurrent prompt may enter a RUNNING turn, got %d accepted", accepted)
 	}
-	if rejectedBusy != prompters-1 {
-		t.Fatalf("every prompt that lost the claim must be rejected with ErrAgentPromptInProgress, got %d of %d", rejectedBusy, prompters-1)
+	if rejectedBusy != prompters {
+		t.Fatalf("every prompt must be rejected with ErrAgentPromptInProgress, got %d of %d", rejectedBusy, prompters)
 	}
 	// The decisive assertion: only one turn was actually started on the agent.
 	agentMgr.mu.Lock()
 	captured := len(agentMgr.capturedPrompts)
 	agentMgr.mu.Unlock()
-	if captured != 1 {
-		t.Fatalf("overlapping turns reached the agent: %d prompts forwarded, want exactly 1", captured)
+	if captured != 0 {
+		t.Fatalf("RUNNING-session prompts reached the agent: %d forwarded, want 0", captured)
 	}
 }
 
@@ -216,10 +209,10 @@ func TestPromptTask_SupersededQueuedDispatchReleasesForegroundClaim(t *testing.T
 	_, err := svc.promptTask(
 		context.Background(), taskID, sessionID, "queued prompt", "", false, nil, false, "stale-entry",
 	)
-	if !errors.Is(err, errQueuedDispatchSuperseded) {
-		t.Fatalf("a dispatch without the current ownership token must be superseded, got: %v", err)
+	if !errors.Is(err, ErrAgentPromptInProgress) {
+		t.Fatalf("a queued dispatch into a RUNNING session must be rejected, got: %v", err)
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("a superseded dispatch must restore the background-idle gate, got %q", got)
 	}
 	if svc.claimForegroundTurn(sessionID) == nil {
@@ -336,7 +329,7 @@ func TestReleaseForegroundClaim_FailedPromptReopensTheGate(t *testing.T) {
 	if claim == nil {
 		t.Fatal("the first prompt must win the claim")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("a claimed turn reads as generating, got %q", got)
 	}
 
@@ -347,7 +340,7 @@ func TestReleaseForegroundClaim_FailedPromptReopensTheGate(t *testing.T) {
 
 	// Background work is still outstanding, so the session is background-idle again
 	// and the operator can retry.
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("a released claim must return the turn to background-idle, got %q", got)
 	}
 	if svc.claimForegroundTurn(sessionID) == nil {
@@ -377,7 +370,7 @@ func TestReleaseForegroundClaim_DoesNotReopenGateWithoutBackgroundWork(t *testin
 		t.Fatal("with no background work outstanding the release must not reopen the gate")
 	}
 
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 		t.Fatalf("with no background work outstanding the turn must read as generating, got %q", got)
 	}
 }
@@ -444,7 +437,7 @@ func TestForegroundDispatch_FailedDispatchRollsBackForRetry(t *testing.T) {
 	if restored := <-rollbackDone; !restored {
 		t.Fatal("an unobserved synchronous dispatch failure must restore background-idle")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("failed dispatch must reopen immediate input, got %q", got)
 	}
 
@@ -464,7 +457,7 @@ func TestForegroundDispatch_FailedDispatchRollsBackForRetry(t *testing.T) {
 		t.Fatal("accepting a retry does not expose background work before foreground idle")
 	}
 	svc.markForegroundIdle(sessionID)
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("accepted retry must retain its own completion/idle identity, got %q", got)
 	}
 }
@@ -503,7 +496,7 @@ func TestForegroundDispatch_StaleRollbackCannotClobberRetry(t *testing.T) {
 	if !svc.markForegroundIdle(sessionID) {
 		t.Fatal("retry's current idle event must expose its background work")
 	}
-	if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+	if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 		t.Fatalf("stale rollback clobbered retry activity: got %q", got)
 	}
 }
@@ -516,13 +509,13 @@ func TestForegroundDispatch_ClaimlessRollbackRestoresOnlyExactUnobservedStart(t
 		svc.registerBackgroundTask(sessionID, "background-1")
 		svc.markForegroundIdle(sessionID)
 		dispatch := svc.beginForegroundDispatch(sessionID, nil)
-		if dispatch == nil || svc.ForegroundActivity(sessionID) != v1.ForegroundActivityGenerating {
+		if dispatch == nil || svc.foregroundActivityValue(sessionID) != v1.ForegroundActivityGenerating {
 			t.Fatal("begin must atomically establish claimless successor ownership")
 		}
 		if !svc.rollbackForegroundDispatch(dispatch) {
 			t.Fatal("exact unobserved failure must restore prior background idle")
 		}
-		if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityBackground {
+		if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityBackground {
 			t.Fatalf("rollback restored %q, want background", got)
 		}
 	})
@@ -538,7 +531,7 @@ func TestForegroundDispatch_ClaimlessRollbackRestoresOnlyExactUnobservedStart(t
 		if svc.rollbackForegroundDispatch(dispatch) {
 			t.Fatal("provider-observed cycle must not roll back")
 		}
-		if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+		if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 			t.Fatalf("provider output lost successor ownership: got %q", got)
 		}
 	})
@@ -560,7 +553,7 @@ func TestForegroundDispatch_ClaimlessRollbackRestoresOnlyExactUnobservedStart(t
 		if svc.rollbackForegroundDispatch(first) {
 			t.Fatal("stale failure token must not restore over retry")
 		}
-		if got := svc.ForegroundActivity(sessionID); got != v1.ForegroundActivityGenerating {
+		if got := svc.foregroundActivityValue(sessionID); got != v1.ForegroundActivityGenerating {
 			t.Fatalf("stale rollback displaced retry: got %q", got)
 		}
 	})
diff --git a/apps/backend/internal/orchestrator/prompt_background_acceptance_test.go b/apps/backend/internal/orchestrator/prompt_background_acceptance_test.go
index 5180ae88aa..094a5b5b41 100644
--- a/apps/backend/internal/orchestrator/prompt_background_acceptance_test.go
+++ b/apps/backend/internal/orchestrator/prompt_background_acceptance_test.go
@@ -11,38 +11,11 @@ import (
 	"github.com/kandev/kandev/internal/task/models"
 )
 
-// TestPromptTask_BackgroundWorkAcceptsInput is the falsifiable acceptance proof
-// for ADR-0049, driven through
-// the REAL operator entrypoint (PromptTask) rather than checkSessionPromptable
-// in isolation — it reproduces the operator-lockout→fixed transition end to end
-// for both of Claude's background-work wire shapes.
-//
-// The symptom: an operator whose agent launched background work (a Monitor
-// watch or a run_in_background shell) is locked out — PromptTask rejects the
-// next message with ErrAgentPromptInProgress because the session state still
-// reads RUNNING, and the only recovery is a service restart. Both shapes only
-// become recognizable on a tool_call_update (the Monitor registration banner
-// seeds its Generic view; the run_in_background flag and command are streamed
-// after the initial empty tool_call), so this exercises the full producer path:
-// a live stream update → background registration → the prompt gate opening.
-//
-// Why #1600 does not already cover this: the upstream idle-turn completion
-// (#1600) only synthesizes a turn-complete after async content has been idle
-// for a ~5s debounce, and a chatty Monitor re-extends that debounce on every
-// event burst — so the synthetic completion never fires while the watch is
-// active. The monitor case below drives repeated event bursts and asserts the
-// session is STILL RUNNING (the #1600 window is open, not closed) before it
-// sends the mid-burst prompt: without the fine-grained gate, that prompt is
-// rejected even though #1600 is armed. See the RED/GREEN note in the batch plan.
-//
-// Deterministic backend integration harness chosen over Playwright by design:
-// surfacing the fine-grained signal to the web composer is a documented
-// follow-up (Batch 2 — the composer still derives "busy" from state ===
-// RUNNING), so a UI test cannot isolate this fix without a timing-flaky
-// assertion. This harness drives PromptTask against a live-agent mock and
-// asserts the message is forwarded to the agent, which is exactly the
-// acceptance the operator sees.
-func TestPromptTask_BackgroundWorkAcceptsInput(t *testing.T) {
+// TestPromptTask_BackgroundWorkStaysBusy drives the real operator entrypoint
+// for both recognized background-work wire shapes. Accounting remains live,
+// but neither a background shell nor a chatty Monitor can bypass the coarse
+// RUNNING gate.
+func TestPromptTask_BackgroundWorkStaysBusy(t *testing.T) {
 	cases := []struct {
 		name       string
 		toolCallID string
@@ -120,10 +93,8 @@ func TestPromptTask_BackgroundWorkAcceptsInput(t *testing.T) {
 			}
 			emitForegroundIdle(svc, taskID, sessionID)
 
-			// The session is still RUNNING: #1600's synthetic turn-complete has not
-			// fired (the bursts kept its debounce alive), so the durable state alone
-			// would keep the operator locked out. This is the window the
-			// fine-grained gate must open.
+			// The session is still RUNNING, so durable state remains the admission
+			// authority regardless of the private background estimate.
 			refreshed, err := repo.GetTaskSession(context.Background(), sessionID)
 			if err != nil {
 				t.Fatalf("reload session: %v", err)
@@ -132,14 +103,100 @@ func TestPromptTask_BackgroundWorkAcceptsInput(t *testing.T) {
 				t.Fatalf("expected session to remain RUNNING while background work is outstanding, got %s", refreshed.State)
 			}
 
-			// Fixed: the same message now goes through — the session accepts input
-			// while only background work is outstanding, and it is forwarded to the
-			// live agent instead of being dropped as "busy".
-			if _, err := svc.PromptTask(context.Background(), taskID, sessionID, "are you still working?", "", false, nil, false); err != nil {
-				t.Fatalf("session with only background work outstanding must accept input, got: %v", err)
+			if _, err := svc.PromptTask(
+				context.Background(), taskID, sessionID, "are you still working?", "", false, nil, false,
+			); !errors.Is(err, ErrAgentPromptInProgress) {
+				t.Fatalf("RUNNING session with background work must reject input, got: %v", err)
+			}
+			if len(agentMgr.capturedPrompts) != 0 {
+				t.Fatalf("rejected prompt reached the agent, captured=%d", len(agentMgr.capturedPrompts))
+			}
+		})
+	}
+}
+
+func TestPromptTask_ClaudeExperimentAdmitsRecognizedBackgroundWork(t *testing.T) {
+	cases := []struct {
+		name       string
+		toolCallID string
+		normalized func() *streams.NormalizedPayload
+	}{
+		{
+			name:       "async subagent",
+			toolCallID: "agent-1",
+			normalized: func() *streams.NormalizedPayload {
+				payload := attestedSubagentPayload("background work", "do it", "general-purpose")
+				payload.SubagentTask().IsAsync = true
+				payload.SetBackgroundWorkIdentity(
+					streams.BackgroundWorkKindSubagent,
+					"child-1",
+					true,
+					false,
+				)
+				return payload
+			},
+		},
+		{
+			name:       "run_in_background shell",
+			toolCallID: "bash-1",
+			normalized: func() *streams.NormalizedPayload {
+				return attestedBackgroundShellPayload("npm run dev")
+			},
+		},
+		{
+			name:       "monitor",
+			toolCallID: "monitor-1",
+			normalized: func() *streams.NormalizedPayload {
+				return monitorGenericPayload(false)
+			},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			repo := setupTestRepo(t)
+			agentMgr := &mockAgentManager{isAgentRunning: true, repoForExecutionLookup: repo}
+			svc := createTestServiceWithAgent(repo, newMockStepGetter(), newMockTaskRepo(), agentMgr)
+			svc.executor = executor.NewExecutor(agentMgr, repo, testLogger(), executor.ExecutorConfig{})
+			svc.messageCreator = &mockMessageCreator{}
+			enableClaudeBackgroundPromptHandoffForTest(t, svc)
+
+			const (
+				taskID    = "task1"
+				sessionID = "session1"
+			)
+			seedTaskAndSession(t, repo, taskID, sessionID, models.TaskSessionStateRunning)
+			setSessionAgentNameForTest(t, svc, sessionID, "claude-acp")
+			session, err := repo.GetTaskSession(context.Background(), sessionID)
+			if err != nil {
+				t.Fatalf("load session: %v", err)
+			}
+			session.AgentExecutionID = "exec-1"
+			seedExecutorRunning(t, repo, sessionID, taskID, "exec-1")
+			if err := repo.UpdateTaskSession(context.Background(), session); err != nil {
+				t.Fatalf("update session: %v", err)
+			}
+
+			svc.handleAgentStreamEvent(context.Background(), &lifecycle.AgentStreamEventPayload{
+				TaskID:      taskID,
+				SessionID:   sessionID,
+				ExecutionID: "exec-1",
+				Data: &lifecycle.AgentStreamEventData{
+					Type:       "tool_update",
+					ToolCallID: tc.toolCallID,
+					ToolStatus: "in_progress",
+					Normalized: tc.normalized(),
+				},
+			})
+			emitForegroundIdle(svc, taskID, sessionID)
+
+			if _, err := svc.PromptTask(
+				context.Background(), taskID, sessionID, "are you still working?", "", false, nil, false,
+			); err != nil {
+				t.Fatalf("enabled Claude background handoff rejected input: %v", err)
 			}
 			if len(agentMgr.capturedPrompts) != 1 {
-				t.Fatalf("accepted prompt must be forwarded to the agent, captured=%d", len(agentMgr.capturedPrompts))
+				t.Fatalf("accepted prompt count = %d, want 1", len(agentMgr.capturedPrompts))
 			}
 		})
 	}
diff --git a/apps/backend/internal/orchestrator/service.go b/apps/backend/internal/orchestrator/service.go
index f015421946..cfb5c44cee 100644
--- a/apps/backend/internal/orchestrator/service.go
+++ b/apps/backend/internal/orchestrator/service.go
@@ -49,9 +49,10 @@ var (
 
 // ServiceConfig holds orchestrator service configuration
 type ServiceConfig struct {
-	Scheduler  scheduler.SchedulerConfig
-	QueueSize  int
-	QueueGroup string
+	Scheduler                     scheduler.SchedulerConfig
+	QueueSize                     int
+	QueueGroup                    string
+	ClaudeBackgroundPromptHandoff bool
 }
 
 // DefaultServiceConfig returns default configuration
@@ -459,8 +460,8 @@ type Service struct {
 	// foregroundActivity tracks, per session, whether the open turn is actively
 	// generating in the foreground or only waiting on a spawned background task
 	// (subagent / run-in-background shell). Keyed sessionID -> *turnActivity;
-	// see turn_activity.go. Consulted by checkSessionPromptable so a session
-	// that kicked off background work still accepts operator input.
+	// see turn_activity.go. This is best-effort accounting state and does not
+	// relax the coarse RUNNING admission policy.
 	// foregroundActivityMu protects record identity: lookups lock the selected
 	// record before releasing it, and execution teardown uses the same order
 	// before detaching an unused record.
@@ -1130,8 +1131,8 @@ func (s *Service) completeTurnForSession(ctx context.Context, sessionID string)
 
 func (s *Service) completeTurnForTaskSession(ctx context.Context, taskID, sessionID string) {
 	// Foreground ownership ends with the turn, but detached background work can
-	// outlive it. Preserve those registrations and expose them as background-idle;
-	// full cleanup belongs to execution/session teardown paths.
+	// outlive it. Preserve those registrations for accounting; full cleanup
+	// belongs to execution/session teardown paths.
 	s.yieldForegroundAndPublish(ctx, taskID, sessionID, foregroundYieldTurnCompletion)
 
 	if s.turnService == nil {
diff --git a/apps/backend/internal/orchestrator/task_operations.go b/apps/backend/internal/orchestrator/task_operations.go
index e0b71b0eee..0a47ac91cf 100644
--- a/apps/backend/internal/orchestrator/task_operations.go
+++ b/apps/backend/internal/orchestrator/task_operations.go
@@ -2975,8 +2975,9 @@ func (s *Service) loadPromptableSession(ctx context.Context, taskID, sessionID s
 	return session, nil
 }
 
-// claimForegroundForPrompt closes the gap between reading a RUNNING session's
-// background-idle substate and dispatching its next prompt.
+// claimForegroundForPrompt serializes two callers racing to take the
+// background-idle foreground turn. For non-experiment RUNNING sessions,
+// checkSessionPromptable already rejects the prompt before this helper is reached.
 func (s *Service) claimForegroundForPrompt(taskID, sessionID string, session *models.TaskSession) (*foregroundClaim, error) {
 	if session.State != models.TaskSessionStateRunning {
 		return nil, nil
@@ -3175,16 +3176,12 @@ func (s *Service) checkSessionPromptable(taskID, sessionID string, state models.
 		models.TaskSessionStateIdle:
 		return nil
 	case models.TaskSessionStateRunning:
-		// Narrow the busy signal: a session that kicked off background work and
-		// is otherwise idle in the foreground should still accept a new message
-		// rather than reporting "running" and dropping it.
-		//
-		// This is a *read*, not a claim — DrainQueuedMessage and the STARTING wait
-		// both call it without going on to drive a turn themselves. PromptTask,
-		// which does, follows a passing read with claimForegroundTurn to close the
-		// check-then-act window against a second concurrent prompt.
-		if !s.isForegroundTurnGenerating(sessionID) {
-			s.logger.Debug("accepting prompt: foreground turn idle, only background work outstanding",
+		// The safe default is coarse: every RUNNING session is busy. A
+		// deployment may explicitly opt a persisted Claude Code session into
+		// ADR-0049's adapter-attested background handoff experiment. Every
+		// missing identity and non-Claude provider still fails closed.
+		if s.ForegroundActivity(sessionID) == v1.ForegroundActivityBackground {
+			s.logger.Debug("accepting prompt: enabled Claude foreground handoff is background-idle",
 				zap.String("task_id", taskID),
 				zap.String("session_id", sessionID))
 			return nil
diff --git a/apps/backend/internal/orchestrator/turn_activity.go b/apps/backend/internal/orchestrator/turn_activity.go
index df490f8b03..9bedaef24c 100644
--- a/apps/backend/internal/orchestrator/turn_activity.go
+++ b/apps/backend/internal/orchestrator/turn_activity.go
@@ -9,6 +9,7 @@ import (
 	"github.com/kandev/kandev/internal/agentctl/types/streams"
 	"github.com/kandev/kandev/internal/events"
 	"github.com/kandev/kandev/internal/events/bus"
+	"github.com/kandev/kandev/internal/task/models"
 	v1 "github.com/kandev/kandev/pkg/api/v1"
 )
 
@@ -16,18 +17,14 @@ import (
 // independently. Foreground activity always has precedence; background work is
 // visible only after an explicit foreground-idle boundary.
 //
-// It is the finer-grained signal behind checkSessionPromptable: a session whose
-// foreground turn has yielded to background work should accept a new message
-// even though its DB state still reads RUNNING. The single-scalar session state
-// cannot tell "the foreground agent is generating" from "the foreground turn is
-// idle but a spawned background task (a subagent, a run-in-background shell) is
-// still running", which is how a long background job used to lock the operator
-// out of the conversation.
+// It is a best-effort accounting signal only. The default admission and public
+// activity contracts never trust it. A high-risk, default-off experiment may
+// use it for persisted Claude Code sessions, whose adapter supplies the
+// recognized lifecycle attestations below.
 //
-// The absent/zero state means "foreground generating": callers default to the
-// pre-existing behaviour (reject a new prompt while RUNNING) unless a background
-// task has been explicitly registered for the session, so nothing changes for a
-// session that has no background work outstanding.
+// The absent/zero internal state means "foreground generating". A recognized
+// registration plus an explicit idle boundary can move only this private
+// estimate to background.
 type turnActivity struct {
 	mu            sync.Mutex
 	revision      uint64                    // invalidates delayed publications after newer mutations
@@ -821,10 +818,8 @@ func (s *Service) clearTurnActivity(sessionID string) {
 // yielded to an outstanding background task. An untracked session defaults to
 // true, preserving the historical "reject a new prompt while RUNNING" contract.
 //
-// This is a pure predicate: checkSessionPromptable and the DTO/WS serializers
-// call it to *report* promptability. A caller that is about to actually drive a
-// turn on the strength of the answer must use claimForegroundTurn instead, or it
-// races every other prompt reading the same window.
+// This is a pure internal predicate. The coarse default admission and
+// serialization seams deliberately do not use it.
 func (s *Service) isForegroundTurnGenerating(sessionID string) bool {
 	ta := s.lockTurnActivity(sessionID, false)
 	if ta == nil {
@@ -845,26 +840,15 @@ func (ta *turnActivity) generatingLocked() bool {
 	return !ta.yielded
 }
 
-// claimForegroundTurn is the check-and-claim half of the background-idle gate.
+// claimForegroundTurn is the retained check-and-claim mechanism for the private
+// background-idle estimate.
 // It atomically verifies the session's foreground turn has yielded to background
 // work and, if so, takes it for the caller by flipping it back to generating —
 // under the same lock, so exactly one caller can win.
 //
-// checkSessionPromptable only *reads* the substate, which leaves a wide
-// check-then-act window in PromptTask: between the gate and the point the turn is
-// finally marked generating sit a session reload, ensureSessionRunning, and an
-// optional (network-bound) model switch. Two prompts arriving in that window —
-// a double-send, or two browser tabs onto the same background-idle session —
-// would both pass the read-only gate and both reach executor.Prompt, starting
-// overlapping turns on one ACP session. Claiming closes that window: the first
-// prompt in wins, and every prompt behind it sees a generating foreground and is
-// rejected with ErrAgentPromptInProgress exactly as it would have been before
-// ADR-0049.
-//
-// The claim is held until agentctl accepts the prompt (beginForegroundDispatch
-// followed by acceptForegroundDispatch — see promptTask in task_operations.go)
-// or it is handed back (releaseForegroundClaim). The returned token binds both
-// operations to this activity record and admission generation.
+// The public coarse gate rejects RUNNING sessions before this is reached unless
+// the Claude-only experiment is enabled. Atomic claims preserve serialization
+// for the experimental path.
 //
 // Returns nil for an untracked session — no background work is outstanding, so
 // there is nothing to claim and the historical reject-while-RUNNING default
@@ -973,7 +957,7 @@ func (s *Service) beginForegroundDispatch(
 	}
 }
 
-// acceptForegroundDispatch closes a background-idle admission claim after
+// acceptForegroundDispatch closes a retained background-idle claim after
 // agentctl acknowledges the prompt. The cycle itself was already established by
 // beginForegroundDispatch, so pre-callback provider events own the right token.
 func (s *Service) acceptForegroundDispatch(dispatch *foregroundDispatch) bool {
@@ -1139,11 +1123,10 @@ func (s *Service) releaseForegroundClaim(claim *foregroundClaim) bool {
 	return true
 }
 
-// foregroundActivityValue reports the fine-grained busy substate of a session
-// for the operator-facing signal: "generating" when the foreground turn is
-// actively producing output (the default), "background" when it has yielded to
-// outstanding spawned work. Background activity can remain meaningful after the
-// coarse session state settles because detached work can outlive a turn.
+// foregroundActivityValue reports the best-effort internal activity estimate.
+// ACP providers do not expose background work with consistent enough lifecycle
+// semantics for this estimate to control operator-facing admission or busy
+// state. Keep it available for dormant tracking and diagnostics only.
 func (s *Service) foregroundActivityValue(sessionID string) v1.ForegroundActivity {
 	if s.isForegroundTurnGenerating(sessionID) {
 		return v1.ForegroundActivityGenerating
@@ -1151,22 +1134,50 @@ func (s *Service) foregroundActivityValue(sessionID string) v1.ForegroundActivit
 	return v1.ForegroundActivityBackground
 }
 
-// ForegroundActivity exposes the in-memory fine-grained busy substate so the
-// page-load / list serialization layer can stamp it onto a session DTO
-// (ADR-0049). This is the same value that drives the
-// live task_session.activity_changed WS event, read straight from the in-memory
-// tracker — the single source of truth. There is no persisted copy. Callers emit
-// generating only for RUNNING sessions, but may emit background for a settled
-// session while its connected execution still has detached work.
-func (s *Service) ForegroundActivity(sessionID string) v1.ForegroundActivity {
-	return s.foregroundActivityValue(sessionID)
+const (
+	claudeACPProviderID = "claude-acp"
+	mockAgentProviderID = "mock-agent"
+)
+
+// claudeBackgroundPromptHandoffEnabled reports whether sessionID is allowed to
+// use the high-risk fine-grained policy. Provider identity comes from the
+// persisted launch snapshot rather than a client-supplied activity value. A
+// missing session, snapshot, or provider fails closed.
+func (s *Service) claudeBackgroundPromptHandoffEnabled(sessionID string) bool {
+	if !s.config.ClaudeBackgroundPromptHandoff || s.repo == nil || sessionID == "" {
+		return false
+	}
+	session, err := s.repo.GetTaskSession(context.Background(), sessionID)
+	if err != nil || session == nil {
+		return false
+	}
+	return s.claudeBackgroundPromptHandoffEnabledForSession(session)
 }
 
-// publishForegroundActivityChanged emits the fine-grained busy signal so the
-// web composer and status indicator can distinguish "generating" from "waiting
-// on background work" without a coarse session-state transition. Callers invoke
-// it only when a flip actually happened (the mark/register/complete helpers
-// return that), so it never fires per background frame.
+func (s *Service) claudeBackgroundPromptHandoffEnabledForSession(
+	session *models.TaskSession,
+) bool {
+	if !s.config.ClaudeBackgroundPromptHandoff || session == nil {
+		return false
+	}
+	agentName, _ := session.AgentProfileSnapshot["agent_name"].(string)
+	return agentName == claudeACPProviderID || agentName == mockAgentProviderID
+}
+
+// ForegroundActivity exposes the conservative operator-facing busy signal by
+// default. A deployment that explicitly enables the experiment may expose the
+// private tracker value only for a persisted Claude Code session (or the mock
+// provider used to exercise Claude lifecycle frames in E2E).
+func (s *Service) ForegroundActivity(sessionID string) v1.ForegroundActivity {
+	if s.claudeBackgroundPromptHandoffEnabled(sessionID) {
+		return s.foregroundActivityValue(sessionID)
+	}
+	return v1.ForegroundActivityGenerating
+}
+
+// publishForegroundActivityChanged emits a provider-aware refresh when the
+// internal tracker changes. publishForegroundActivityNow applies the coarse
+// default or the explicitly enabled Claude experiment before broadcasting.
 func (s *Service) publishForegroundActivityChanged(ctx context.Context, taskID, sessionID string) {
 	publicationLock, releasePublication := s.acquireActivityPublicationGuard(sessionID)
 	defer releasePublication()
@@ -1239,7 +1250,7 @@ func (s *Service) publishForegroundActivityNow(
 	eventData := map[string]interface{}{
 		metaKeyTaskID:           taskID,
 		metaKeySessionID:        sessionID,
-		"foreground_activity":   value,
+		"foreground_activity":   s.publicForegroundActivityValue(ctx, sessionID, value),
 		"active_subagent_count": activeSubagentCount,
 	}
 	if err := s.eventBus.Publish(ctx, events.TaskSessionActivityChanged,
@@ -1255,6 +1266,32 @@ func (s *Service) publishForegroundActivityNow(
 	s.publishTaskActivityIfChanged(ctx, taskID)
 }
 
+func (s *Service) publicForegroundActivityValue(
+	ctx context.Context,
+	sessionID string,
+	value interface{},
+) interface{} {
+	if value == nil {
+		return nil
+	}
+	publicValue := interface{}(string(v1.ForegroundActivityGenerating))
+	if s.repo == nil {
+		return publicValue
+	}
+	session, err := s.repo.GetTaskSession(ctx, sessionID)
+	if err != nil || session == nil {
+		return publicValue
+	}
+	if s.claudeBackgroundPromptHandoffEnabledForSession(session) &&
+		value == string(v1.ForegroundActivityBackground) {
+		return value
+	}
+	if session.State != models.TaskSessionStateRunning {
+		return nil
+	}
+	return publicValue
+}
+
 // normalizedIsBackgroundTask reports whether the adapter attested a live
 // workload whose complete lifecycle Kandev recognizes.
 //
diff --git a/apps/backend/internal/profiles/profiles.yaml b/apps/backend/internal/profiles/profiles.yaml
index 8a015e3973..5b20a95f53 100644
--- a/apps/backend/internal/profiles/profiles.yaml
+++ b/apps/backend/internal/profiles/profiles.yaml
@@ -67,6 +67,13 @@ features:
     dev:  "false"
     e2e:  "false"
 
+  # High-risk Claude-only background prompt handoff experiment. Off in every
+  # profile so it is exercised only by contributors who deliberately opt in.
+  KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF:
+    prod: "false"
+    dev:  "false"
+    e2e:  "false"
+
 # ── Mock providers ────────────────────────────────────────────────
 # Swap real third-party services for in-memory fakes. Production
 # leaves all of these unset (real APIs). Dev opts into the mock agent
diff --git a/apps/backend/internal/profiles/profiles_test.go b/apps/backend/internal/profiles/profiles_test.go
index 5087c1e109..70784303b8 100644
--- a/apps/backend/internal/profiles/profiles_test.go
+++ b/apps/backend/internal/profiles/profiles_test.go
@@ -22,8 +22,8 @@ func TestApplyProfile_DefaultsToProd(t *testing.T) {
 		t.Errorf("env = %q, want %q (no selector env vars set)", env, EnvProd)
 	}
 	// Prod writes each registered feature flag with its safe shipped default.
-	if count != 4 {
-		t.Errorf("ApplyProfile wrote %d vars in prod; want 4", count)
+	if count != 5 {
+		t.Errorf("ApplyProfile wrote %d vars in prod; want 5", count)
 	}
 	if v := os.Getenv("KANDEV_FEATURES_OFFICE"); v != "false" {
 		t.Errorf("KANDEV_FEATURES_OFFICE = %q after prod ApplyProfile; want %q", v, "false")
@@ -37,6 +37,13 @@ func TestApplyProfile_DefaultsToProd(t *testing.T) {
 	if v := os.Getenv("KANDEV_FEATURES_AUTH"); v != "false" {
 		t.Errorf("KANDEV_FEATURES_AUTH = %q after prod ApplyProfile; want %q", v, "false")
 	}
+	if v := os.Getenv("KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF"); v != "false" {
+		t.Errorf(
+			"KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF = %q after prod ApplyProfile; want %q",
+			v,
+			"false",
+		)
+	}
 }
 
 // TestApplyProfile_DevUsesDevelopmentDefaults verifies the mixed dev profile:
@@ -67,6 +74,13 @@ func TestApplyProfile_DevUsesDevelopmentDefaults(t *testing.T) {
 	if v := os.Getenv("KANDEV_FEATURES_AUTH"); v != "false" {
 		t.Errorf("KANDEV_FEATURES_AUTH = %q in dev; want %q", v, "false")
 	}
+	if v := os.Getenv("KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF"); v != "false" {
+		t.Errorf(
+			"KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF = %q in dev; want %q",
+			v,
+			"false",
+		)
+	}
 }
 
 // TestApplyProfile_E2EWinsOverDev checks the documented detection
@@ -92,6 +106,13 @@ func TestApplyProfile_E2EWinsOverDev(t *testing.T) {
 	if v := os.Getenv("AGENTCTL_AUTO_APPROVE_PERMISSIONS"); v != "true" {
 		t.Errorf("AGENTCTL_AUTO_APPROVE_PERMISSIONS = %q in e2e; want %q", v, "true")
 	}
+	if v := os.Getenv("KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF"); v != "false" {
+		t.Errorf(
+			"KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF = %q in e2e; want %q",
+			v,
+			"false",
+		)
+	}
 }
 
 // TestApplyProfile_ExistingEnvWins is the precedence guarantee that
@@ -154,6 +175,13 @@ func TestFeatureFlagDefaults_LowercasesShortName(t *testing.T) {
 	if _, ok := defaults["app_status_bar"]; !ok {
 		t.Errorf("FeatureFlagDefaults missing %q key; got %#v", "app_status_bar", defaults)
 	}
+	if _, ok := defaults["claude_background_prompt_handoff"]; !ok {
+		t.Errorf(
+			"FeatureFlagDefaults missing %q key; got %#v",
+			"claude_background_prompt_handoff",
+			defaults,
+		)
+	}
 }
 
 func TestMarkApplied_OnlyAllowsKnownDerivedEnvVars(t *testing.T) {
@@ -181,7 +209,15 @@ func TestMarkApplied_OnlyAllowsKnownDerivedEnvVars(t *testing.T) {
 // hell out of whoever debugs it.
 func TestProfilesYAML_ContainsRequiredSections(t *testing.T) {
 	yaml := string(ProfilesYAML())
-	for _, section := range []string{"features:", "mocks:", "debug:", "KANDEV_FEATURES_OFFICE:", "KANDEV_FEATURES_PLUGINS:", "KANDEV_FEATURES_APP_STATUS_BAR:"} {
+	for _, section := range []string{
+		"features:",
+		"mocks:",
+		"debug:",
+		"KANDEV_FEATURES_OFFICE:",
+		"KANDEV_FEATURES_PLUGINS:",
+		"KANDEV_FEATURES_APP_STATUS_BAR:",
+		"KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF:",
+	} {
 		if !strings.Contains(yaml, section) {
 			t.Errorf("embedded profiles.yaml missing section/key %q; embed broken or file truncated", section)
 		}
diff --git a/apps/backend/internal/runtimeflags/config.go b/apps/backend/internal/runtimeflags/config.go
index af69a35c6b..138494d13f 100644
--- a/apps/backend/internal/runtimeflags/config.go
+++ b/apps/backend/internal/runtimeflags/config.go
@@ -9,18 +9,20 @@ import (
 )
 
 const (
-	featureOfficeKey        = "features.office"
-	featurePluginsKey       = "features.plugins"
-	featureAppStatusBarKey  = "features.appStatusBar"
-	featureAuthKey          = "features.auth"
-	debugDevModeKey         = "debug.devMode"
-	envFeaturesOffice       = "KANDEV_FEATURES_OFFICE"
-	envFeaturesPlugins      = "KANDEV_FEATURES_PLUGINS"
-	envFeaturesAppStatusBar = "KANDEV_FEATURES_APP_STATUS_BAR"
-	envFeaturesAuth         = "KANDEV_FEATURES_AUTH"
-	envDebugDevMode         = "KANDEV_DEBUG_DEV_MODE"
-	envDebugPprofEnabled    = "KANDEV_DEBUG_PPROF_ENABLED"
-	envDebugAgentMessages   = "KANDEV_DEBUG_AGENT_MESSAGES"
+	featureOfficeKey                         = "features.office"
+	featurePluginsKey                        = "features.plugins"
+	featureAppStatusBarKey                   = "features.appStatusBar"
+	featureAuthKey                           = "features.auth"
+	featureClaudeBackgroundPromptHandoffKey  = "features.claudeBackgroundPromptHandoff"
+	debugDevModeKey                          = "debug.devMode"
+	envFeaturesOffice                        = "KANDEV_FEATURES_OFFICE"
+	envFeaturesPlugins                       = "KANDEV_FEATURES_PLUGINS"
+	envFeaturesAppStatusBar                  = "KANDEV_FEATURES_APP_STATUS_BAR"
+	envFeaturesAuth                          = "KANDEV_FEATURES_AUTH"
+	envFeaturesClaudeBackgroundPromptHandoff = "KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF"
+	envDebugDevMode                          = "KANDEV_DEBUG_DEV_MODE"
+	envDebugPprofEnabled                     = "KANDEV_DEBUG_PPROF_ENABLED"
+	envDebugAgentMessages                    = "KANDEV_DEBUG_AGENT_MESSAGES"
 )
 
 func OptionsFromConfig(cfg *config.Config) Options {
@@ -32,9 +34,12 @@ func OptionsFromConfig(cfg *config.Config) Options {
 			envFeaturesPlugins:      isTruthy(os.Getenv(envFeaturesPlugins)),
 			envFeaturesAppStatusBar: isTruthy(os.Getenv(envFeaturesAppStatusBar)),
 			envFeaturesAuth:         isTruthy(os.Getenv(envFeaturesAuth)),
-			envDebugDevMode:         isTruthy(os.Getenv(envDebugDevMode)),
-			envDebugPprofEnabled:    isTruthy(os.Getenv(envDebugPprofEnabled)),
-			envDebugAgentMessages:   isTruthy(os.Getenv(envDebugAgentMessages)),
+			envFeaturesClaudeBackgroundPromptHandoff: isTruthy(
+				os.Getenv(envFeaturesClaudeBackgroundPromptHandoff),
+			),
+			envDebugDevMode:       isTruthy(os.Getenv(envDebugDevMode)),
+			envDebugPprofEnabled:  isTruthy(os.Getenv(envDebugPprofEnabled)),
+			envDebugAgentMessages: isTruthy(os.Getenv(envDebugAgentMessages)),
 		},
 		IsExplicitEnv: func(name string) bool {
 			_, ok := os.LookupEnv(name)
@@ -46,11 +51,12 @@ func OptionsFromConfig(cfg *config.Config) Options {
 func ValuesFromConfig(cfg *config.Config) map[string]bool {
 	debugEnabled := cfg.Debug.DevMode || cfg.Debug.PprofEnabled
 	return map[string]bool{
-		featureOfficeKey:       cfg.Features.Office,
-		featurePluginsKey:      cfg.Features.Plugins,
-		featureAppStatusBarKey: cfg.Features.AppStatusBar,
-		featureAuthKey:         cfg.Features.Auth,
-		debugDevModeKey:        debugEnabled,
+		featureOfficeKey:                        cfg.Features.Office,
+		featurePluginsKey:                       cfg.Features.Plugins,
+		featureAppStatusBarKey:                  cfg.Features.AppStatusBar,
+		featureAuthKey:                          cfg.Features.Auth,
+		featureClaudeBackgroundPromptHandoffKey: cfg.Features.ClaudeBackgroundPromptHandoff,
+		debugDevModeKey:                         debugEnabled,
 	}
 }
 
@@ -65,6 +71,8 @@ func ApplyStatesToConfig(cfg *config.Config, states []RuntimeFlagState) {
 			cfg.Features.AppStatusBar = state.EffectiveValue
 		case featureAuthKey:
 			cfg.Features.Auth = state.EffectiveValue
+		case featureClaudeBackgroundPromptHandoffKey:
+			cfg.Features.ClaudeBackgroundPromptHandoff = state.EffectiveValue
 		case debugDevModeKey:
 			cfg.Debug.DevMode = state.EffectiveValue
 			cfg.Debug.PprofEnabled = state.EffectiveValue
diff --git a/apps/backend/internal/runtimeflags/config_test.go b/apps/backend/internal/runtimeflags/config_test.go
index c17cfdaa16..eb2b2c03aa 100644
--- a/apps/backend/internal/runtimeflags/config_test.go
+++ b/apps/backend/internal/runtimeflags/config_test.go
@@ -2,6 +2,7 @@ package runtimeflags
 
 import (
 	"os"
+	"reflect"
 	"testing"
 
 	"github.com/kandev/kandev/internal/common/config"
@@ -80,6 +81,17 @@ func TestOptionsFromConfigParsesUppercaseTruthyEnvForAppStatusBar(t *testing.T)
 	}
 }
 
+func TestOptionsFromConfigParsesClaudeBackgroundPromptHandoffEnv(t *testing.T) {
+	preserveEnv(t, "KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF")
+	t.Setenv("KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF", "TRUE")
+
+	opts := OptionsFromConfig(&config.Config{})
+
+	if !opts.EnvValues["KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF"] {
+		t.Fatal("KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF TRUE parsed false, want true")
+	}
+}
+
 func TestValuesFromConfigIncludesPlugins(t *testing.T) {
 	cfg := &config.Config{}
 	cfg.Features.Plugins = true
@@ -125,6 +137,34 @@ func TestValuesFromConfigIncludesAppStatusBar(t *testing.T) {
 	}
 }
 
+func TestValuesFromConfigIncludesClaudeBackgroundPromptHandoff(t *testing.T) {
+	cfg := &config.Config{}
+	field := reflect.ValueOf(&cfg.Features).Elem().FieldByName("ClaudeBackgroundPromptHandoff")
+	if !field.IsValid() {
+		t.Fatal("FeaturesConfig.ClaudeBackgroundPromptHandoff field missing")
+	}
+	field.SetBool(true)
+
+	values := ValuesFromConfig(cfg)
+
+	if !values["features.claudeBackgroundPromptHandoff"] {
+		t.Fatal("ValuesFromConfig did not surface features.claudeBackgroundPromptHandoff = true")
+	}
+}
+
+func TestApplyStatesToConfigSetsClaudeBackgroundPromptHandoff(t *testing.T) {
+	cfg := &config.Config{}
+	ApplyStatesToConfig(cfg, []RuntimeFlagState{{
+		Key:            "features.claudeBackgroundPromptHandoff",
+		EffectiveValue: true,
+	}})
+
+	field := reflect.ValueOf(&cfg.Features).Elem().FieldByName("ClaudeBackgroundPromptHandoff")
+	if !field.IsValid() || !field.Bool() {
+		t.Fatal("ApplyStatesToConfig did not set Features.ClaudeBackgroundPromptHandoff = true")
+	}
+}
+
 func TestApplyStatesToConfigMarksImpliedDebugEnvAsApplied(t *testing.T) {
 	for _, name := range []string{
 		"KANDEV_DEBUG_PPROF_ENABLED",
diff --git a/apps/backend/internal/runtimeflags/registry.go b/apps/backend/internal/runtimeflags/registry.go
index cb9da90dd8..cfcbf1870d 100644
--- a/apps/backend/internal/runtimeflags/registry.go
+++ b/apps/backend/internal/runtimeflags/registry.go
@@ -56,6 +56,20 @@ var definitions = []RuntimeFlagDefinition{
 		RestartRequired: true,
 		Mutable:         true,
 	},
+	{
+		Key:         featureClaudeBackgroundPromptHandoffKey,
+		EnvVar:      envFeaturesClaudeBackgroundPromptHandoff,
+		Kind:        KindFeature,
+		Label:       "Claude background prompt handoff",
+		Description: "Allows Claude Code to accept a new prompt after its foreground yields while recognized background work remains active.",
+		Stability:   StabilityExperimental,
+		RiskLevel:   RiskHigh,
+		RiskDescription: "Claude ACP background lifecycle signals can be missing, delayed, duplicated, or ambiguous. " +
+			"Enabling this experiment can misclassify session activity or dispatch overlapping prompts. " +
+			"Use it only for controlled testing and disable it if a session behaves unexpectedly.",
+		RestartRequired: true,
+		Mutable:         true,
+	},
 	{
 		Key:         debugDevModeKey,
 		EnvVar:      envDebugDevMode,
diff --git a/apps/backend/internal/runtimeflags/registry_test.go b/apps/backend/internal/runtimeflags/registry_test.go
index 36f0f3e7e8..1f2fe6d804 100644
--- a/apps/backend/internal/runtimeflags/registry_test.go
+++ b/apps/backend/internal/runtimeflags/registry_test.go
@@ -53,6 +53,34 @@ func TestDefinitionsIncludeAppStatusBarMetadata(t *testing.T) {
 	}
 }
 
+func TestDefinitionsIncludeClaudeBackgroundPromptHandoffMetadata(t *testing.T) {
+	def, ok := DefinitionByKey("features.claudeBackgroundPromptHandoff")
+	if !ok {
+		t.Fatal("features.claudeBackgroundPromptHandoff definition missing")
+	}
+	if def.EnvVar != "KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF" {
+		t.Fatalf(
+			"EnvVar = %q, want KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF",
+			def.EnvVar,
+		)
+	}
+	if def.Stability != StabilityExperimental {
+		t.Fatalf("Stability = %q, want %q", def.Stability, StabilityExperimental)
+	}
+	if def.RiskLevel != RiskHigh {
+		t.Fatalf("RiskLevel = %q, want %q", def.RiskLevel, RiskHigh)
+	}
+	if def.RiskDescription == "" {
+		t.Fatal("RiskDescription empty")
+	}
+	if !def.RestartRequired {
+		t.Fatal("RestartRequired = false, want true")
+	}
+	if !def.Mutable {
+		t.Fatal("Mutable = false, want true")
+	}
+}
+
 func TestDefinitionsExposeSingleUserFacingDebugToggle(t *testing.T) {
 	def, ok := DefinitionByKey("debug.devMode")
 	if !ok {
diff --git a/apps/backend/internal/task/handlers/message_handlers.go b/apps/backend/internal/task/handlers/message_handlers.go
index 8f0c73adf8..0e4db2ca21 100644
--- a/apps/backend/internal/task/handlers/message_handlers.go
+++ b/apps/backend/internal/task/handlers/message_handlers.go
@@ -32,20 +32,9 @@ type OrchestratorService interface {
 	StartCreatedSession(ctx context.Context, taskID, sessionID, agentProfileID, prompt string, skipMessageRecord, planMode, autoStart bool, attachments []v1.MessageAttachment, references []v1.EntityReference) error
 	ProcessOnTurnStart(ctx context.Context, taskID, sessionID string) error
 	StepRequiresCompletionSignal(ctx context.Context, taskID string) bool
-	// ForegroundActivity reports the fine-grained busy substate of a RUNNING
-	// session (ADR-0049): "background" when the foreground turn has yielded to
-	// spawned background work and can accept a new message.
-	//
-	// Deliberately a hard dependency here, unlike TaskHandlers — which reaches the
-	// same method through an optional type-assertion on OrchestratorStarter and
-	// simply omits the field when it isn't there. The asymmetry is the difference
-	// in blast radius, not an oversight: this is the admission gate, so an
-	// orchestrator that silently lacked the method would fall back to rejecting
-	// every RUNNING session and quietly un-ship the feature. Requiring it makes
-	// that a compile error. TaskHandlers only enriches a DTO with the substate; if
-	// it's absent the client just falls back to the safe "generating" default, so
-	// there a soft dependency costs nothing. Resist "fixing" the inconsistency by
-	// making this one optional.
+	// ForegroundActivity is already filtered by the orchestrator's runtime flag
+	// and persisted provider identity. Background therefore means this exact
+	// session is eligible for the experimental direct-admission path.
 	ForegroundActivity(sessionID string) v1.ForegroundActivity
 }
 
@@ -436,11 +425,8 @@ func (h *MessageHandlers) resolveSessionAfterTurnStart(
 func (h *MessageHandlers) errorForBlockedMessageSession(msg *ws.Message, sessionID string, state models.TaskSessionState) *ws.Message {
 	switch state {
 	case models.TaskSessionStateRunning:
-		// A RUNNING session whose foreground turn has yielded to spawned
-		// background work (ADR-0049) accepts a new message: it flows on to
-		// PromptTask, which owns the same foreground-idle gate and forwards it.
-		// Only a foreground-generating turn is blocked here.
-		if h.orchestrator != nil && h.orchestrator.ForegroundActivity(sessionID) == v1.ForegroundActivityBackground {
+		if h.orchestrator != nil &&
+			h.orchestrator.ForegroundActivity(sessionID) == v1.ForegroundActivityBackground {
 			return nil
 		}
 		wsErr, _ := ws.NewError(msg.ID, msg.Action, ws.ErrorCodeValidation, "Agent is currently processing. Please wait for the current operation to complete.", nil)
diff --git a/apps/backend/internal/task/handlers/message_handlers_blocked_test.go b/apps/backend/internal/task/handlers/message_handlers_blocked_test.go
index b5ab423e85..c92a858d81 100644
--- a/apps/backend/internal/task/handlers/message_handlers_blocked_test.go
+++ b/apps/backend/internal/task/handlers/message_handlers_blocked_test.go
@@ -644,8 +644,8 @@ func TestWSAddMessageFailsWhenSessionReloadAfterOnTurnStartFails(t *testing.T) {
 	assert.Empty(t, orch.getForwardedSession())
 }
 
-// fgActivityOrchestrator is a minimal OrchestratorService whose ForegroundActivity
-// is configurable, for testing the ADR-0049 message-add gate.
+// fgActivityOrchestrator retains a configurable legacy activity value to prove
+// message admission ignores it.
 type fgActivityOrchestrator struct {
 	activity v1.ForegroundActivity
 }
@@ -697,7 +697,7 @@ func TestWSAddMessage_ForegroundActivityAdmissionWiring(t *testing.T) {
 		wantPrompt   bool
 	}{
 		{
-			name:         "running background dispatches prompt",
+			name:         "running eligible background is accepted",
 			state:        models.TaskSessionStateRunning,
 			activity:     v1.ForegroundActivityBackground,
 			wantResponse: ws.MessageTypeResponse,
@@ -772,11 +772,11 @@ func TestWSAddMessage_ForegroundActivityAdmissionWiring(t *testing.T) {
 	}
 }
 
-// TestErrorForBlockedMessageSession_BackgroundIdleAccepts is the ADR-0049
-// message-add gate: a RUNNING session whose foreground turn has yielded to
-// background work must NOT be blocked at the message.add layer (it flows on to
-// PromptTask), while a foreground-generating RUNNING session stays blocked.
-func TestErrorForBlockedMessageSession_BackgroundIdleAccepts(t *testing.T) {
+// TestErrorForBlockedMessageSession_RunningAlwaysBlocks proves a legacy
+// TestErrorForBlockedMessageSession_UsesOrchestratorActivityPolicy proves the
+// transport accepts only the provider/flag-filtered background value returned
+// by the orchestrator while retaining the coarse block for generating turns.
+func TestErrorForBlockedMessageSession_UsesOrchestratorActivityPolicy(t *testing.T) {
 	log, err := logger.NewLogger(logger.LoggingConfig{Level: "error", Format: "json"})
 	require.NoError(t, err)
 	msg := &ws.Message{ID: "1", Action: ws.ActionMessageAdd}
@@ -788,7 +788,7 @@ func TestErrorForBlockedMessageSession_BackgroundIdleAccepts(t *testing.T) {
 		wantBlock bool
 	}{
 		{"running + generating is blocked", v1.ForegroundActivityGenerating, models.TaskSessionStateRunning, true},
-		{"running + background is accepted", v1.ForegroundActivityBackground, models.TaskSessionStateRunning, false},
+		{"running + eligible background is accepted", v1.ForegroundActivityBackground, models.TaskSessionStateRunning, false},
 		{"waiting is accepted regardless", v1.ForegroundActivityGenerating, models.TaskSessionStateWaitingForInput, false},
 		{"failed stays blocked", v1.ForegroundActivityBackground, models.TaskSessionStateFailed, true},
 	}
diff --git a/apps/web/e2e/tests/chat/busy-signal.spec.ts b/apps/web/e2e/tests/chat/busy-signal.spec.ts
index 5fd163147a..a26f0bd87a 100644
--- a/apps/web/e2e/tests/chat/busy-signal.spec.ts
+++ b/apps/web/e2e/tests/chat/busy-signal.spec.ts
@@ -2,24 +2,10 @@ import { type Page } from "@playwright/test";
 import { test, expect } from "../../fixtures/test-base";
 import type { SeedData } from "../../fixtures/test-base";
 import type { ApiClient } from "../../helpers/api-client";
-import { typeWhileBusy } from "../../helpers/type-while-busy";
 import { waitForActiveSessionForegroundActivity } from "../../helpers/session-store";
+import { typeWhileBusy } from "../../helpers/type-while-busy";
 import { SessionPage } from "../../pages/session-page";
 
-// ---------------------------------------------------------------------------
-// ADR-0049 — operator-visible surfacing.
-//
-// The mock `/detached-background <dur>` command returns its foreground response
-// immediately while the launched workload continues, so this suite exercises
-// work that genuinely outlives the foreground turn.
-//
-// The distinguishing observable of the background-idle window (b) is that the
-// agent status still reads "running" (the working affordance) WHILE the composer
-// shows its idle/accept placeholder — condition (a), a genuinely generating
-// turn, keeps the "Queue more instructions…" busy placeholder and diverts input
-// to the queue.
-// ---------------------------------------------------------------------------
-
 async function seedTaskAndWaitForIdle(
   testPage: Page,
   apiClient: ApiClient,
@@ -39,18 +25,16 @@ async function seedTaskAndWaitForIdle(
   );
 
   await testPage.goto(`/t/${task.id}`);
-
   const session = new SessionPage(testPage);
   await session.waitForLoad();
   await session.waitForChatIdle({ timeout: 30_000 });
-
   return session;
 }
 
-test.describe("Fine-grained busy signal — composer + status", () => {
+test.describe("Coarse RUNNING busy signal", () => {
   test.describe.configure({ retries: 1 });
 
-  test("async subagent accepts a new foreground turn and clears on singleton ID-less completion", async ({
+  test("held-open background turn remains busy across input and reload", async ({
     testPage,
     apiClient,
     seedData,
@@ -61,194 +45,39 @@ test.describe("Fine-grained busy signal — composer + status", () => {
       testPage,
       apiClient,
       seedData,
-      "Async subagent lifecycle",
+      "Coarse busy signal",
     );
 
-    // This replay is deliberately ordered like Claude's async Agent path:
-    // Agent launch (with agentId) -> human-origin foreground idle -> final
-    // same-prompt thought/message -> prompt completion -> Claude's ID-less
-    // task-notification completion. It is not the shell-background ordering
-    // covered below. Exact-ID completion is pinned by backend unit coverage;
-    // this browser path exercises the safe singleton fallback Claude requires.
-    await session.sendMessage("/async-subagent-lifecycle 20s");
-    await expect(testPage.getByText("Foreground response after async launch.")).toBeVisible({
-      timeout: 20_000,
+    await session.sendMessage("/background 30s");
+    await expect(session.agentStatus()).toBeVisible({ timeout: 15_000 });
+    await expect(testPage.getByText("Kicking off background work")).toBeVisible({
+      timeout: 15_000,
     });
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-    const backgroundIndicator = session
-      .sidebarTaskItem("Async subagent lifecycle")
-      .getByTestId("task-state-background-running");
-    await expect(backgroundIndicator).toBeVisible();
-    await expect(backgroundIndicator).toHaveClass(/text-violet-500/);
-    await expect(backgroundIndicator).toHaveClass(/animate-spin/);
-    await expect(backgroundIndicator.locator("..")).toHaveAttribute(
-      "aria-label",
-      "Background work is running",
-    );
+    // The foreground-idle frame follows this text in the mock's ordered ACP
+    // stream. Allow the subsequent WS publication to settle before asserting
+    // the stable composer contract.
+    await testPage.waitForTimeout(500);
 
-    // A prompt submitted while only the async child remains must be admitted
-    // immediately. Foreground activity temporarily wins over the child.
-    await session.sendMessage("/slow 2s");
-    await expect(testPage.getByText("/slow 2s")).toBeVisible({ timeout: 15_000 });
-    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
+    // The private tracker may identify background work, but the public
+    // contract remains coarse for the entire RUNNING turn.
     await waitForActiveSessionForegroundActivity(testPage, "generating");
-
-    // The older async child remains visible after the second foreground yields,
-    // then its singleton ID-less task-notification removes the final registration.
-    await expect(session.idleInput()).toBeVisible({ timeout: 15_000 });
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-    await waitForActiveSessionForegroundActivity(testPage, null);
-    await expect(backgroundIndicator).not.toBeVisible();
-  });
-
-  test("execution teardown clears an async child whose completion never arrives", async ({
-    testPage,
-    apiClient,
-    seedData,
-  }) => {
-    test.setTimeout(90_000);
-
-    const task = await apiClient.createTaskWithAgent(
-      seedData.workspaceId,
-      "Async subagent teardown",
-      seedData.agentProfileId,
-      {
-        description: "/async-subagent-teardown",
-        workflow_id: seedData.workflowId,
-        workflow_step_id: seedData.startStepId,
-        repository_ids: [seedData.repositoryId],
-      },
-    );
-    if (!task.session_id) throw new Error("auto-started task did not return a session id");
-
-    await testPage.goto(`/t/${task.id}`);
-    const session = new SessionPage(testPage);
-    await session.waitForLoad();
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-
-    // No child completion is emitted by this scenario. The terminal execution
-    // boundary must reconcile its owned registration instead.
-    await apiClient.stopSession({
-      session_id: task.session_id,
-      reason: "e2e teardown",
-      force: true,
-    });
-    await expect(session.agentStatus()).not.toBeVisible({ timeout: 20_000 });
-    await waitForActiveSessionForegroundActivity(testPage, null);
-    await expect(session.agentStatus()).not.toBeVisible();
-  });
-
-  test("background-idle session shows working AND accepts input, then flips to done", async ({
-    testPage,
-    apiClient,
-    seedData,
-  }) => {
-    test.setTimeout(90_000);
-
-    const session = await seedTaskAndWaitForIdle(testPage, apiClient, seedData, "Busy signal (b)");
-
-    // Launch work whose foreground prompt closes immediately.
-    await session.sendMessage("/detached-background 12s");
-
-    // The turn is working…
-    await expect(session.agentStatus()).toBeVisible({ timeout: 15_000 });
-
-    // …and once it yields to background work the composer flips to accept-input
-    // (idle placeholder) even though the status still reads "running": the two
-    // independent facts — "you may type" AND "work is still in progress" — are
-    // both visible at once. This is the whole point of the fine-grained signal.
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-
-    // The working affordance must NOT be the done state while background runs.
-    // Once the detached workload completes, the working affordance clears.
-    await expect(session.agentStatus()).not.toBeVisible({ timeout: 40_000 });
-    await expect(session.idleInput()).toBeVisible({ timeout: 10_000 });
-  });
-
-  test("input typed during the background-idle window is sent, not queued", async ({
-    testPage,
-    apiClient,
-    seedData,
-  }) => {
-    test.setTimeout(90_000);
-
-    const session = await seedTaskAndWaitForIdle(testPage, apiClient, seedData, "Busy signal send");
-
-    await session.sendMessage("/detached-background 20s");
-    await expect(session.agentStatus()).toBeVisible({ timeout: 15_000 });
-
-    // Wait for the background-idle window (accept-input while still working).
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-
-    // Type and submit a foreground turn — it is accepted and posted, not
-    // diverted, and foreground busy temporarily takes absolute precedence.
-    const editor = testPage.locator(".tiptap.ProseMirror").first();
-    await editor.click();
-    await editor.fill("/slow 3s");
-    const modifier = process.platform === "darwin" ? "Meta" : "Control";
-    await editor.press(`${modifier}+Enter`);
-
-    // It appears in the conversation as a sent user message…
-    await expect(testPage.getByText("/slow 3s")).toBeVisible({ timeout: 15_000 });
-    // …and was NOT silently diverted to the queue.
-    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
-
-    // While that foreground is active, the instant-send placeholder disappears
-    // even though the older detached workload remains registered.
-    await expect(session.idleInput()).not.toBeVisible({ timeout: 2_000 });
+    await expect(session.idleInput()).not.toBeVisible();
     await expect(testPage.locator('[data-placeholder^="Queue"]')).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "generating");
 
-    // Foreground completion reveals the still-running detached work again.
-    await expect(session.idleInput()).toBeVisible({ timeout: 15_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-  });
+    const editor = session.activeChat().locator(".tiptap.ProseMirror:visible");
+    await typeWhileBusy(testPage, editor, "queue this follow-up");
+    await testPage.getByTestId("submit-message-button").click();
+    await expect(testPage.getByTestId("queue-chip")).toBeVisible({ timeout: 10_000 });
 
-  test("background-idle substate survives a fresh page reload (boot payload, no WS flip)", async ({
-    testPage,
-    apiClient,
-    seedData,
-  }) => {
-    test.setTimeout(90_000);
-
-    const session = await seedTaskAndWaitForIdle(
-      testPage,
-      apiClient,
-      seedData,
-      "Busy signal reload",
-    );
-
-    // Open a long background window so it is still held after the reload lands.
-    await session.sendMessage("/detached-background 20s");
-    await expect(session.agentStatus()).toBeVisible({ timeout: 15_000 });
-
-    // Reach the background-idle window: accept-input while still working.
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
-    await expect(session.agentStatus()).toBeVisible();
-
-    // Reload: this is a fresh client that loads MID background-window. The
-    // substate is not persisted and no activity_changed WS flip is due, so the
-    // only way the composer can
-    // show accept-input + working here is if the boot payload carried the
-    // fine-grained substate. This is the exact gap this batch closes: before it,
-    // a reload showed the coarse "Queue more instructions…" busy affordance until
-    // the next flip — which, for a genuinely idle-on-background turn, never comes.
     await testPage.reload();
     await session.waitForLoad();
-
-    await expect(session.idleInput()).toBeVisible({ timeout: 15_000 });
     await expect(session.agentStatus()).toBeVisible();
+    await waitForActiveSessionForegroundActivity(testPage, "generating");
+    await expect(session.idleInput()).not.toBeVisible();
+    await expect(testPage.locator('[data-placeholder^="Queue"]')).toBeVisible();
   });
 
-  test("a turn with no background work keeps the composer gated (queues input)", async ({
+  test("foreground generation continues to queue input", async ({
     testPage,
     apiClient,
     seedData,
@@ -259,24 +88,116 @@ test.describe("Fine-grained busy signal — composer + status", () => {
       testPage,
       apiClient,
       seedData,
-      "Busy signal gated",
+      "Coarse busy foreground",
     );
 
-    // A plain slow turn generates in the foreground the whole time — no
-    // recognized background work — so the composer stays gated exactly as today.
     await session.sendMessage("/slow 10s");
     await expect(session.agentStatus()).toBeVisible({ timeout: 15_000 });
+    await waitForActiveSessionForegroundActivity(testPage, "generating");
 
-    // The accept-input (idle) placeholder must NOT appear while generating.
-    await expect(session.idleInput()).not.toBeVisible();
-
-    const editor = testPage.locator(".tiptap.ProseMirror").first();
-    await typeWhileBusy(testPage, editor, "should queue");
-    const submitBtn = testPage.getByTestId("submit-message-button");
-    await expect(submitBtn).toBeVisible({ timeout: 5_000 });
-    await submitBtn.click();
-
-    // Diverted to the queue, not posted — the historical contract is unchanged.
+    const editor = session.activeChat().locator(".tiptap.ProseMirror:visible");
+    await typeWhileBusy(testPage, editor, "queue foreground follow-up");
+    await testPage.getByTestId("submit-message-button").click();
     await expect(testPage.getByTestId("queue-chip")).toBeVisible({ timeout: 10_000 });
   });
 });
+
+test.describe.serial("Claude background prompt handoff experiment", () => {
+  test.describe.configure({ retries: 1 });
+
+  test.beforeAll(async ({ backend }) => {
+    await backend.restart({
+      KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF: "true",
+    });
+    const response = await fetch(`${backend.baseUrl}/api/v1/features`);
+    expect(response.ok).toBeTruthy();
+    expect(await response.json()).toMatchObject({
+      claudeBackgroundPromptHandoff: true,
+    });
+  });
+
+  test.afterAll(async ({ backend }) => {
+    await backend.restart();
+  });
+
+  test("async subagent accepts a foreground turn and clears on completion", async ({
+    testPage,
+    apiClient,
+    seedData,
+  }) => {
+    test.setTimeout(120_000);
+
+    const session = await seedTaskAndWaitForIdle(
+      testPage,
+      apiClient,
+      seedData,
+      "Experimental async subagent",
+    );
+    const agentName = await testPage.evaluate(() => {
+      const store = (
+        window as Window & {
+          __KANDEV_E2E_STORE__?: {
+            getState: () => {
+              tasks: { activeSessionId: string | null };
+              taskSessions: { items: Record<string, Record<string, unknown>> };
+            };
+          };
+        }
+      ).__KANDEV_E2E_STORE__;
+      const state = store?.getState();
+      const sessionID = state?.tasks.activeSessionId;
+      const snapshot = sessionID
+        ? (state?.taskSessions.items[sessionID]?.agent_profile_snapshot as
+            | Record<string, unknown>
+            | undefined)
+        : undefined;
+      return snapshot?.agent_name;
+    });
+    expect(agentName).toBe("mock-agent");
+
+    await session.sendMessage("/async-subagent-lifecycle 12s");
+    await expect(testPage.getByText("Foreground response after async launch.")).toBeVisible({
+      timeout: 20_000,
+    });
+    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
+    await waitForActiveSessionForegroundActivity(testPage, "background");
+
+    await session.sendMessage("/slow 2s");
+    await expect(testPage.getByText("/slow 2s")).toBeVisible({ timeout: 15_000 });
+    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
+    await waitForActiveSessionForegroundActivity(testPage, "generating");
+    await expect(session.idleInput()).toBeVisible({ timeout: 15_000 });
+    await waitForActiveSessionForegroundActivity(testPage, "background");
+    await waitForActiveSessionForegroundActivity(testPage, null);
+  });
+
+  test("detached work accepts input and preserves the background state on reload", async ({
+    testPage,
+    apiClient,
+    seedData,
+  }) => {
+    test.setTimeout(120_000);
+
+    const session = await seedTaskAndWaitForIdle(
+      testPage,
+      apiClient,
+      seedData,
+      "Experimental detached work",
+    );
+
+    await session.sendMessage("/detached-background 20s");
+    await expect(session.agentStatus()).toBeVisible({ timeout: 15_000 });
+    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
+    await waitForActiveSessionForegroundActivity(testPage, "background");
+
+    await testPage.reload();
+    await session.waitForLoad();
+    await expect(session.agentStatus()).toBeVisible();
+    await expect(session.idleInput()).toBeVisible({ timeout: 15_000 });
+    await waitForActiveSessionForegroundActivity(testPage, "background");
+
+    await session.sendMessage("/slow 2s");
+    await expect(testPage.getByText("/slow 2s")).toBeVisible({ timeout: 15_000 });
+    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
+  });
+});
diff --git a/apps/web/e2e/tests/chat/mobile-busy-signal.spec.ts b/apps/web/e2e/tests/chat/mobile-busy-signal.spec.ts
index daf7fce52f..767ba3fe60 100644
--- a/apps/web/e2e/tests/chat/mobile-busy-signal.spec.ts
+++ b/apps/web/e2e/tests/chat/mobile-busy-signal.spec.ts
@@ -1,114 +1,24 @@
 import { test, expect } from "../../fixtures/test-base";
-import { SessionPage } from "../../pages/session-page";
 import { waitForActiveSessionForegroundActivity } from "../../helpers/session-store";
+import { typeWhileBusy } from "../../helpers/type-while-busy";
+import { SessionPage } from "../../pages/session-page";
 
-// Mobile (Pixel 5) coverage for ADR-0049. Filename matches
-// /mobile-.*\.spec\.ts/ so the `mobile-chrome` project picks it up. The composer
-// gating and the working affordance derive from the same shared hooks the
-// desktop path uses, so this asserts the operator-visible outcome holds at
-// mobile width: a background-idle session shows "working" while the composer
-// accepts input, then flips to done once the background task finishes.
-
-test.describe("Mobile fine-grained busy signal", () => {
+test.describe("Mobile coarse RUNNING busy signal", () => {
   test.describe.configure({ retries: 1 });
 
-  test("async subagent allows instant mobile send and clears on singleton ID-less completion", async ({
-    testPage,
-    apiClient,
-    seedData,
-  }) => {
-    test.setTimeout(150_000);
-
-    const task = await apiClient.createTaskWithAgent(
-      seedData.workspaceId,
-      "Mobile async subagent lifecycle",
-      seedData.agentProfileId,
-      {
-        description: "/async-subagent-lifecycle 25s",
-        workflow_id: seedData.workflowId,
-        workflow_step_id: seedData.startStepId,
-        repository_ids: [seedData.repositoryId],
-      },
-    );
-
-    await testPage.goto(`/t/${task.id}`);
-    const session = new SessionPage(testPage);
-    await session.waitForLoad();
-    await expect(testPage.getByText("Foreground response after async launch.")).toBeVisible({
-      timeout: 25_000,
-    });
-    await expect(session.idleInput()).toBeVisible({ timeout: 25_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-
-    // Use the shipped Pixel 5 composer button path; the prompt must be posted,
-    // not queued, and foreground must take visual precedence over the child.
-    await session.sendMessageViaButton("/slow 3s");
-    await expect(testPage.getByText("/slow 3s")).toBeVisible({ timeout: 15_000 });
-    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "generating");
-
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-    await expect(session.agentStatus()).not.toBeVisible({ timeout: 45_000 });
-    await waitForActiveSessionForegroundActivity(testPage, null);
-    await expect(session.agentStatus()).not.toBeVisible();
-  });
-
-  test("execution teardown clears a missing async completion on mobile", async ({
-    testPage,
-    apiClient,
-    seedData,
-  }) => {
-    test.setTimeout(100_000);
-
-    const task = await apiClient.createTaskWithAgent(
-      seedData.workspaceId,
-      "Mobile async subagent teardown",
-      seedData.agentProfileId,
-      {
-        description: "/async-subagent-teardown",
-        workflow_id: seedData.workflowId,
-        workflow_step_id: seedData.startStepId,
-        repository_ids: [seedData.repositoryId],
-      },
-    );
-    if (!task.session_id) throw new Error("auto-started task did not return a session id");
-
-    await testPage.goto(`/t/${task.id}`);
-    const session = new SessionPage(testPage);
-    await session.waitForLoad();
-    await expect(session.idleInput()).toBeVisible({ timeout: 25_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-
-    await apiClient.stopSession({
-      session_id: task.session_id,
-      reason: "e2e teardown",
-      force: true,
-    });
-    await expect(session.agentStatus()).not.toBeVisible({ timeout: 20_000 });
-    await waitForActiveSessionForegroundActivity(testPage, null);
-    await expect(session.agentStatus()).not.toBeVisible();
-  });
-
-  test("background-idle session shows working AND accepts input at mobile width", async ({
+  test("held-open background turn remains busy across input and reload", async ({
     testPage,
     apiClient,
     seedData,
   }) => {
     test.setTimeout(120_000);
 
-    // Drive the background window via the auto-started first turn (the task
-    // description) rather than a sendMessage follow-up: the live turn reliably
-    // reaches the mobile client while it is still running (same approach as
-    // mobile-empty-turn.spec.ts).
     const task = await apiClient.createTaskWithAgent(
       seedData.workspaceId,
-      "Mobile busy signal",
+      "Mobile coarse busy signal",
       seedData.agentProfileId,
       {
-        description: "/detached-background 30s",
+        description: "/background 30s",
         workflow_id: seedData.workflowId,
         workflow_step_id: seedData.startStepId,
         repository_ids: [seedData.repositoryId],
@@ -118,50 +28,56 @@ test.describe("Mobile fine-grained busy signal", () => {
     await testPage.goto(`/t/${task.id}`);
     const session = new SessionPage(testPage);
     await session.waitForLoad();
-
-    // The auto-started turn is working…
     await expect(session.agentStatus()).toBeVisible({ timeout: 20_000 });
+    await expect(testPage.getByText("Kicking off background work")).toBeVisible({
+      timeout: 20_000,
+    });
+    await testPage.waitForTimeout(500);
 
-    // …and once it yields to background work the composer flips to accept-input
-    // (idle placeholder) while the status still reads "working" — both facts
-    // visible at once at mobile width.
-    await expect(session.idleInput()).toBeVisible({ timeout: 25_000 });
-    await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
-
-    // A mobile button submission during the background-only window must start
-    // a new foreground turn immediately, never divert the prompt to the queue.
-    await session.sendMessageViaButton("/slow 5s");
-    await expect(testPage.getByText("/slow 5s")).toBeVisible({ timeout: 15_000 });
-    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
-    await expect(session.idleInput()).not.toBeVisible({ timeout: 5_000 });
     await waitForActiveSessionForegroundActivity(testPage, "generating");
+    await expect(session.idleInput()).not.toBeVisible();
+    await expect(testPage.locator('[data-placeholder^="Queue"]')).toBeVisible();
 
-    // Foreground completion exposes the older detached work again until its
-    // own lifecycle completion arrives.
-    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
+    const editor = session.activeChat().locator(".tiptap.ProseMirror:visible");
+    await typeWhileBusy(testPage, editor, "queue this mobile follow-up");
+    await testPage.getByTestId("submit-message-button").tap();
+    await expect(testPage.getByTestId("queue-chip")).toBeVisible({ timeout: 10_000 });
+
+    await testPage.reload();
+    await session.waitForLoad();
     await expect(session.agentStatus()).toBeVisible();
-    await waitForActiveSessionForegroundActivity(testPage, "background");
+    await waitForActiveSessionForegroundActivity(testPage, "generating");
+    await expect(session.idleInput()).not.toBeVisible();
+    await expect(testPage.locator('[data-placeholder^="Queue"]')).toBeVisible();
+  });
+});
 
-    // After the detached task completes, the working affordance clears.
-    await expect(session.agentStatus()).not.toBeVisible({ timeout: 40_000 });
-    await expect(session.idleInput()).toBeVisible({ timeout: 10_000 });
+test.describe.serial("Mobile Claude background prompt handoff experiment", () => {
+  test.describe.configure({ retries: 1 });
+
+  test.beforeAll(async ({ backend }) => {
+    await backend.restart({
+      KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF: "true",
+    });
   });
 
-  test("background-idle substate survives a reload at mobile width", async ({
+  test.afterAll(async ({ backend }) => {
+    await backend.restart();
+  });
+
+  test("background-only work keeps working visible while input sends immediately", async ({
     testPage,
     apiClient,
     seedData,
   }) => {
-    test.setTimeout(90_000);
+    test.setTimeout(120_000);
 
-    // Long background window so it is still held after the reload lands.
     const task = await apiClient.createTaskWithAgent(
       seedData.workspaceId,
-      "Mobile busy signal reload",
+      "Mobile experimental background handoff",
       seedData.agentProfileId,
       {
-        description: "/detached-background 20s",
+        description: "/e2e:simple-message",
         workflow_id: seedData.workflowId,
         workflow_step_id: seedData.startStepId,
         repository_ids: [seedData.repositoryId],
@@ -171,19 +87,22 @@ test.describe("Mobile fine-grained busy signal", () => {
     await testPage.goto(`/t/${task.id}`);
     const session = new SessionPage(testPage);
     await session.waitForLoad();
+    await session.waitForChatIdle({ timeout: 30_000 });
 
-    // Reach the background-idle window.
+    const editor = session.activeChat().locator(".tiptap.ProseMirror:visible");
+    await editor.tap();
+    await editor.fill("/detached-background 20s");
+    await testPage.getByTestId("submit-message-button").tap();
     await expect(session.agentStatus()).toBeVisible({ timeout: 20_000 });
-    await expect(session.idleInput()).toBeVisible({ timeout: 25_000 });
-    await expect(session.agentStatus()).toBeVisible();
+    await expect(session.idleInput()).toBeVisible({ timeout: 20_000 });
+    await waitForActiveSessionForegroundActivity(testPage, "background");
 
-    // Reload mid-window: a fresh mobile client. The accept-input + working
-    // affordance must come straight from the boot payload (no persisted value,
-    // no activity_changed WS flip due) — ADR-0049.
-    await testPage.reload();
-    await session.waitForLoad();
+    await editor.tap();
+    await editor.fill("/slow 2s");
+    await testPage.getByTestId("submit-message-button").tap();
 
-    await expect(session.idleInput()).toBeVisible({ timeout: 15_000 });
-    await expect(session.agentStatus()).toBeVisible();
+    await expect(testPage.getByText("/slow 2s")).toBeVisible({ timeout: 15_000 });
+    await expect(testPage.getByTestId("queue-chip")).not.toBeVisible();
+    await waitForActiveSessionForegroundActivity(testPage, "generating");
   });
 });
diff --git a/apps/web/lib/state/slices/features/features-slice.test.ts b/apps/web/lib/state/slices/features/features-slice.test.ts
index 5c7f15cc27..b5307fdb90 100644
--- a/apps/web/lib/state/slices/features/features-slice.test.ts
+++ b/apps/web/lib/state/slices/features/features-slice.test.ts
@@ -24,24 +24,34 @@ describe("features slice", () => {
     expect(store.getState().features.plugins).toBe(false);
     expect(defaultFeaturesState.features).toHaveProperty("appStatusBar", false);
     expect(defaultFeaturesState.features).toHaveProperty("auth", false);
+    expect(defaultFeaturesState.features).toHaveProperty("claudeBackgroundPromptHandoff", false);
   });
 
   it("setFeatures replaces the whole flag map", () => {
     const store = makeStore();
-    store.getState().setFeatures({ office: true, plugins: true, appStatusBar: true, auth: true });
+    store.getState().setFeatures({
+      office: true,
+      plugins: true,
+      appStatusBar: true,
+      auth: true,
+      claudeBackgroundPromptHandoff: true,
+    });
     expect(store.getState().features.office).toBe(true);
     expect(store.getState().features.plugins).toBe(true);
     expect(store.getState().features.appStatusBar).toBe(true);
     expect(store.getState().features.auth).toBe(true);
+    expect(store.getState().features.claudeBackgroundPromptHandoff).toBe(true);
     store.getState().setFeatures({
       office: false,
       plugins: false,
       appStatusBar: false,
       auth: false,
+      claudeBackgroundPromptHandoff: false,
     });
     expect(store.getState().features.office).toBe(false);
     expect(store.getState().features.plugins).toBe(false);
     expect(store.getState().features.appStatusBar).toBe(false);
     expect(store.getState().features.auth).toBe(false);
+    expect(store.getState().features.claudeBackgroundPromptHandoff).toBe(false);
   });
 });
diff --git a/apps/web/lib/state/slices/features/features-slice.ts b/apps/web/lib/state/slices/features/features-slice.ts
index efd1e9fd51..9b952370f6 100644
--- a/apps/web/lib/state/slices/features/features-slice.ts
+++ b/apps/web/lib/state/slices/features/features-slice.ts
@@ -10,6 +10,7 @@ export const defaultFeaturesState: FeaturesSliceState = {
     plugins: false,
     appStatusBar: false,
     auth: false,
+    claudeBackgroundPromptHandoff: false,
   },
 };
 
diff --git a/apps/web/lib/state/slices/features/types.ts b/apps/web/lib/state/slices/features/types.ts
index 91e02a0928..5ed63c9e04 100644
--- a/apps/web/lib/state/slices/features/types.ts
+++ b/apps/web/lib/state/slices/features/types.ts
@@ -9,6 +9,7 @@ export type FeatureFlags = {
   plugins: boolean;
   appStatusBar: boolean;
   auth: boolean;
+  claudeBackgroundPromptHandoff: boolean;
 };
 
 export type FeatureName = keyof FeatureFlags;
diff --git a/docs/decisions/0049-fine-grained-foreground-idle-busy-signal.md b/docs/decisions/0049-fine-grained-foreground-idle-busy-signal.md
index ec6cf62fa4..e1ec4bd0dc 100644
--- a/docs/decisions/0049-fine-grained-foreground-idle-busy-signal.md
+++ b/docs/decisions/0049-fine-grained-foreground-idle-busy-signal.md
@@ -1,6 +1,6 @@
 # 0049: Fine-grained foreground-idle busy signal
 
-**Status:** accepted (amended 2026-07-26)
+**Status:** superseded by 2026-07-28-coarse-running-busy-signal
 **Date:** 2026-07-11
 **Area:** backend, frontend, protocol
 **Related:** [Background work liveness spec](../specs/platform/background-work-liveness.md)
diff --git a/docs/decisions/2026-07-28-coarse-running-busy-signal.md b/docs/decisions/2026-07-28-coarse-running-busy-signal.md
new file mode 100644
index 0000000000..e6e4c92e15
--- /dev/null
+++ b/docs/decisions/2026-07-28-coarse-running-busy-signal.md
@@ -0,0 +1,74 @@
+# ADR-2026-07-28-coarse-running-busy-signal: Default to Coarse Running Prompt Admission
+
+**Status:** accepted
+**Date:** 2026-07-28
+**Area:** backend, frontend, protocol
+
+## Context
+
+ADR-0049 allowed a `RUNNING` session to accept input when Kandev inferred that
+the foreground had yielded to recognized background work. In practice, ACP
+providers do not report subagent and background-work lifecycles with enough
+consistent identity, nesting, or terminal-state detail to make that inference a
+reliable admission boundary. Misclassification can enable overlapping prompts,
+show an incorrect background status, or leave a session transition waiting on
+an event the provider never emits.
+
+## Decision
+
+Restore the conservative pre-ADR-0049 operator contract as the shipped default:
+
+- Every `RUNNING` session rejects direct prompt admission and routes composer
+  input through the existing queued-message path.
+- Every `RUNNING` session is exposed as `foreground_activity=generating`.
+  Settled sessions do not expose a background activity tier.
+- `session.activity_changed`, `session.state_changed`, boot payloads, REST
+  session DTOs, and task aggregates follow the same coarse activity policy.
+- The in-memory background-work tracker and adapter attestations remain in place
+  as accounting infrastructure. They may continue to supply
+  `active_subagent_count`, but they do not relax admission or select an
+  operator-visible background activity tier by default.
+
+Retain ADR-0049's complete Claude Code behavior behind the default-off
+`features.claudeBackgroundPromptHandoff` runtime toggle. The exception is
+effective only for `claude-acp` sessions (plus the mock provider in E2E):
+
+- adapter-attested Claude subagents, background shells, and Monitor watches may
+  expose the background activity tier;
+- a generation-matched Claude foreground handoff may admit the next prompt
+  while the durable session remains `RUNNING`; and
+- every other provider remains coarse even when the toggle is enabled.
+
+The toggle is experimental, high risk, restart-required, and off in every
+embedded profile. Missing provider identity fails closed. Its purpose is to let
+designated contributors gather protocol fixtures and refine the behavior
+without changing the release default.
+
+## Consequences
+
+Prompt admission is safe and consistent across ACP providers by default, and
+the composer cannot advertise direct input that the coarse lifecycle considers
+busy. An operator may need to queue a follow-up while a held-open foreground
+turn waits on background work. Detached work that outlives a completed
+foreground turn is not shown as a distinct background-running tier unless the
+Claude experiment is deliberately enabled.
+
+The opt-in path preserves a focused real-world test bed without exposing known
+ACP lifecycle uncertainty to every user. Enabling it accepts the original
+risks: missing, delayed, duplicated, or ID-less Claude lifecycle frames can
+misclassify activity or promptability. The environment variable or persisted
+runtime override provides a kill switch, but it does not make those signals
+authoritative.
+
+## Alternatives Considered
+
+- **Revert ADR-0049 and all implementation commits.** Rejected because later
+  lifecycle hardening and accounting work spans many subsystems; removing it
+  immediately creates more release risk than disabling the policy boundary.
+- **Disable only prompt admission.** Rejected because the UI would still
+  advertise direct input or a background state that no longer controls
+  admission.
+- **Remove the fine-grained path completely.** Rejected because a default-off,
+  Claude-scoped experiment gives the original contributor a controlled way to
+  reproduce and improve all supported background modes without changing the
+  release default.
diff --git a/docs/decisions/INDEX.md b/docs/decisions/INDEX.md
index 52842b8e0f..676484268d 100644
--- a/docs/decisions/INDEX.md
+++ b/docs/decisions/INDEX.md
@@ -56,7 +56,7 @@ Read individual ADRs for full context. Create new ones via `/record decision` or
 | 0046 | [Settings route save coordinator](0046-settings-route-save-coordinator.md)                                                          | accepted   | frontend                    | 2026-07-14 |
 | 0047 | [Plugins read conversation content via a capability-gated Host RPC](0047-plugin-host-conversation-reads.md)                          | accepted   | backend, protocol           | 2026-07-21 |
 | 0048 | [Plugins invoke a settings-selectable utility agent](0048-plugin-host-utility-agent-invoke.md)                                       | accepted   | backend, frontend, protocol | 2026-07-21 |
-| 0049 | [Fine-grained foreground-idle busy signal](0049-fine-grained-foreground-idle-busy-signal.md)                                      | accepted (amended 2026-07-26) | backend, frontend, protocol | 2026-07-11 |
+| 0049 | [Fine-grained foreground-idle busy signal](0049-fine-grained-foreground-idle-busy-signal.md)                                      | superseded by 2026-07-28-coarse-running-busy-signal | backend, frontend, protocol | 2026-07-11 |
 | 0050 | [Plugins provide OIDC/SAML login via a capability-gated, host-minted session](0050-plugin-external-auth-capability.md)               | accepted   | backend, security, protocol | 2026-07-26 |
 | 2026-07-23-opencode-review-evidence-trust | [Trusted OpenCode Review Evidence](2026-07-23-opencode-review-evidence-trust.md) | accepted | workflow, infra | 2026-07-23 |
 | 2026-07-23-planner-direct-small-work | [Planner Direct Small Work](2026-07-23-planner-direct-small-work.md) | superseded by 2026-07-26 | workflow | 2026-07-23 |
@@ -83,3 +83,4 @@ Read individual ADRs for full context. Create new ones via `/record decision` or
 | 2026-07-27-task-git-credential-policy | [Separate GitHub Automation From Task Git Credential Policy](2026-07-27-task-git-credential-policy.md) | accepted | backend, frontend, security | 2026-07-27 |
 | 2026-07-27-legacy-add-branch-live-rescan | [Preserve Live Rescan for Legacy Add Branch](2026-07-27-legacy-add-branch-live-rescan.md) | accepted | backend, protocol | 2026-07-27 |
 | 2026-07-28-visible-wip-overflow-queues | [Separate Visible Queueing From WIP Admission](2026-07-28-visible-wip-overflow-queues.md) | proposed | backend, frontend, protocol, workflow | 2026-07-28 |
+| 2026-07-28-coarse-running-busy-signal | [Restore Coarse Running Prompt Admission](2026-07-28-coarse-running-busy-signal.md) | accepted | backend, frontend, protocol | 2026-07-28 |
diff --git a/docs/plans/coarse-running-busy-signal/plan.md b/docs/plans/coarse-running-busy-signal/plan.md
new file mode 100644
index 0000000000..2a7bb8fdb6
--- /dev/null
+++ b/docs/plans/coarse-running-busy-signal/plan.md
@@ -0,0 +1,75 @@
+---
+spec: docs/specs/platform/background-work-liveness.md
+created: 2026-07-28
+status: completed
+---
+
+# Implementation Plan: Coarse Running Default with Claude Experiment
+
+## Overview
+
+Restore the pre-ADR-0049 admission and display contract as the default while
+leaving ADR-0049's complete Claude behavior available behind a default-off,
+high-risk runtime flag. Pin both sides of the contract with focused backend
+tests and desktop/mobile browser coverage, then update the public configuration
+and API documentation.
+
+## Backend
+
+### Admission and exposed activity
+
+- Update `apps/backend/internal/orchestrator/task_operations.go` so
+  `checkSessionPromptable` rejects every `RUNNING` session with
+  `ErrAgentPromptInProgress`.
+- Update `apps/backend/internal/orchestrator/turn_activity.go` so
+  `ForegroundActivity` and activity publications expose only the coarse
+  generating policy while the private tracker retains its fine-grained value.
+- Update `publishTaskSessionStateChanged` in
+  `apps/backend/internal/orchestrator/event_handlers_streaming.go` to use the
+  same public policy and omit activity after `RUNNING`.
+- Add `features.claudeBackgroundPromptHandoff` and require both that flag and an
+  exact `claude-acp` provider snapshot before the private tracker can relax
+  admission or expose the background tier. The mock provider follows this path
+  only for E2E coverage.
+
+## Frontend
+
+The existing composer, activity store, and status components already consume
+the backend's `foreground_activity`. Add the flag to the shared feature shape;
+the backend remains authoritative for whether a specific session is eligible.
+
+## Tests
+
+- **What:** a `RUNNING` background-idle session remains unpromptable.
+  **File:** `apps/backend/internal/orchestrator/foreground_busy_signal_test.go`.
+  **How:** drive the real tracker into background-idle, assert the private value
+  remains available, then assert the public admission and activity seams remain
+  coarse.
+- **What:** live activity publications never advertise the dormant background
+  tier. **File:**
+  `apps/backend/internal/orchestrator/foreground_activity_signal_test.go`.
+  **How:** publish a background-idle transition through the recording event bus
+  and assert `generating`.
+
+## E2E Tests
+
+- **Scenario:** GIVEN a held-open background turn on desktop, WHEN the operator
+  submits during its background-idle window, THEN the composer queues the
+  message and remains generating across reload.
+  **File:** `apps/web/e2e/tests/chat/busy-signal.spec.ts`.
+- **Scenario:** the same user outcome through the existing mobile composer
+  button on Pixel 5.
+  **File:** `apps/web/e2e/tests/chat/mobile-busy-signal.spec.ts`.
+- **Scenario:** with the flag explicitly enabled, the complete desktop and
+  mobile Claude-mock suite covers async subagents, detached work, foreground
+  precedence, reload hydration, and touch submission. Backend prompt-entry
+  tests cover every recognized Claude mode, including `run_in_background`
+  shells and Monitor.
+
+No layout, navigation, scroll, or touch composition changes are required. Both
+viewports reuse the shipped session composer and status surfaces.
+
+## Implementation Waves
+
+- [x] [Task 01: Restore coarse running policy](task-01-restore-coarse-running-policy.md)
+- [x] [Task 02: Add Claude experiment flag](task-02-add-claude-experiment-flag.md)
diff --git a/docs/plans/coarse-running-busy-signal/task-01-restore-coarse-running-policy.md b/docs/plans/coarse-running-busy-signal/task-01-restore-coarse-running-policy.md
new file mode 100644
index 0000000000..683c3d185c
--- /dev/null
+++ b/docs/plans/coarse-running-busy-signal/task-01-restore-coarse-running-policy.md
@@ -0,0 +1,75 @@
+---
+id: "01-restore-coarse-running-policy"
+title: "Restore coarse running policy"
+status: completed
+wave: 1
+depends_on: []
+plan: "plan.md"
+spec: "../../specs/platform/background-work-liveness.md"
+---
+
+# Task 01: Restore coarse running policy
+
+## Acceptance
+
+- Every `RUNNING` session rejects direct prompt admission even when the private
+  tracker reports foreground-idle background work.
+- Boot/REST/WS/task activity surfaces expose `generating` for `RUNNING` and do
+  not expose a settled background tier.
+- Desktop and mobile composer flows queue input during a held-open background
+  turn and retain that behavior after a fresh reload.
+
+## Verification
+
+- `make -C apps/backend test`
+- `cd apps && pnpm --filter @kandev/web e2e:run -- tests/chat/busy-signal.spec.ts -- --grep "held-open background turn remains busy"`
+- `cd apps && pnpm --filter @kandev/web e2e:run -- tests/chat/mobile-busy-signal.spec.ts -- --grep "held-open background turn remains busy"`
+- `make fmt`
+- `make typecheck test lint`
+
+## Files likely touched
+
+- `apps/backend/internal/orchestrator/task_operations.go`
+- `apps/backend/internal/orchestrator/turn_activity.go`
+- `apps/backend/internal/orchestrator/event_handlers_streaming.go`
+- `apps/backend/internal/orchestrator/foreground_busy_signal_test.go`
+- `apps/backend/internal/orchestrator/foreground_activity_signal_test.go`
+- `apps/web/e2e/tests/chat/busy-signal.spec.ts`
+- `apps/web/e2e/tests/chat/mobile-busy-signal.spec.ts`
+- `docs/specs/platform/background-work-liveness.md`
+- `docs/decisions/0049-fine-grained-foreground-idle-busy-signal.md`
+- `docs/decisions/2026-07-28-coarse-running-busy-signal.md`
+- `docs/decisions/INDEX.md`
+- `docs/public/tasks-and-workflows.md`
+- `docs/public/websocket-api.md`
+
+## Dependencies
+
+None.
+
+## Parallelism
+
+Sequential. Admission and all activity surfaces share one policy boundary.
+
+## Inputs
+
+- Background work liveness spec: coarse admission and display scenarios.
+- ADR-2026-07-28: retain dormant accounting while disabling policy use.
+- Existing tracker and busy-signal tests around ADR-0049.
+
+## Output contract
+
+Report the root cause, files changed, RED/GREEN evidence, E2E results, required
+verification results, commit receipt, remaining risks, and task/plan status.
+
+## Results
+
+- RED: targeted orchestrator tests failed because background-idle was admitted
+  and exported as `background`; desktop and mobile E2E timed out waiting for the
+  coarse `generating` value.
+- GREEN: targeted orchestrator and mock-agent regressions passed.
+- GREEN: desktop Chromium and mobile Chrome held-open background scenarios
+  queued input and remained generating across reload.
+- GREEN: `make fmt`.
+- GREEN: `make typecheck test lint`.
+- GREEN: public documentation validation tests and source validation.
diff --git a/docs/plans/coarse-running-busy-signal/task-02-add-claude-experiment-flag.md b/docs/plans/coarse-running-busy-signal/task-02-add-claude-experiment-flag.md
new file mode 100644
index 0000000000..a7cae76076
--- /dev/null
+++ b/docs/plans/coarse-running-busy-signal/task-02-add-claude-experiment-flag.md
@@ -0,0 +1,74 @@
+---
+id: "02-add-claude-experiment-flag"
+title: "Add Claude background prompt handoff experiment"
+status: completed
+wave: 2
+depends_on: ["01-restore-coarse-running-policy"]
+plan: "plan.md"
+spec: "../../specs/platform/background-work-liveness.md"
+---
+
+# Task 02: Add Claude background prompt handoff experiment
+
+## Acceptance
+
+- `features.claudeBackgroundPromptHandoff` is experimental, high risk,
+  restart-required, and off in prod, dev, and E2E unless explicitly overridden.
+- Flag off preserves Task 01's coarse admission and activity behavior.
+- Flag on restores every ADR-0049 background mode for `claude-acp` sessions.
+- Flag on never relaxes admission or activity for another real provider.
+- Desktop and mobile Playwright cover both the default and opt-in contracts.
+
+## Verification
+
+- Targeted config, runtime-flag, orchestrator, handler, and frontend tests.
+- Targeted desktop and mobile Playwright for coarse and experimental behavior.
+- `make fmt`
+- `make typecheck test lint`
+- Public documentation validation.
+
+## Files likely touched
+
+- `apps/backend/internal/profiles/profiles.yaml`
+- `apps/backend/internal/common/config/config.go`
+- `apps/backend/internal/runtimeflags/`
+- `apps/backend/internal/backendapp/orchestrator.go`
+- `apps/backend/internal/orchestrator/`
+- `apps/backend/internal/task/handlers/message_handlers.go`
+- `apps/web/lib/state/slices/features/`
+- `apps/web/e2e/tests/chat/`
+- `docs/decisions/2026-07-28-coarse-running-busy-signal.md`
+- `docs/specs/platform/background-work-liveness.md`
+- `docs/public/configuration.md`
+- `docs/public/tasks-and-workflows.md`
+- `docs/public/websocket-api.md`
+
+## Dependencies
+
+Task 01 supplies the safe default and retains the internal tracker.
+
+## Parallelism
+
+Sequential. The config, admission, publication, and client contracts must use
+one policy and be proven together.
+
+## Verification Results
+
+- `make fmt` — passed.
+- `make typecheck test lint` — passed:
+  - Go suite, including orchestrator concurrency tests.
+  - Web: 922 files passed; 7,050 tests passed; 4 skipped.
+  - CLI: 30 files and 280 tests passed.
+  - Backend, web, and harness lint passed.
+- `cd apps && pnpm --filter @kandev/web e2e:run --host tests/chat/busy-signal.spec.ts`
+  — default-off desktop
+  cases passed; the first opt-in run found and drove the persisted provider
+  discriminator fix (`agent_name`, not the database UUID in `agent_id`).
+- `cd apps && pnpm --filter @kandev/web e2e:run --host --no-build tests/chat/busy-signal.spec.ts -- --grep "Claude background prompt handoff experiment"`
+  — 2 passed.
+- `cd apps && pnpm --filter @kandev/web e2e:run --host --no-build --project mobile-chrome tests/chat/mobile-busy-signal.spec.ts`
+  — default-off mobile passed; the opt-in test exposed a desktop-keyboard test
+  helper mismatch.
+- `cd apps && pnpm --filter @kandev/web e2e:run --host --no-build --project mobile-chrome tests/chat/mobile-busy-signal.spec.ts -- --grep "background-only work"`
+  — 1 passed after switching the mobile flow to touch submission.
+- Public documentation validation passed as part of `make test`.
diff --git a/docs/public/configuration.md b/docs/public/configuration.md
index ca589ad338..6835615561 100644
--- a/docs/public/configuration.md
+++ b/docs/public/configuration.md
@@ -118,6 +118,7 @@ The launcher starts `agentctl`, performs a one-time nonce handshake, and supplie
 | `features.office` | `KANDEV_FEATURES_OFFICE` | `false` in production | Experimental Office UI, routes, services, and automation. |
 | `features.plugins` | `KANDEV_FEATURES_PLUGINS` | `false` in production | Extensible plugin system: install/manage plugins, spawn plugin backends, and load native UI bundles. Loaded plugin code runs with backend privileges. |
 | `features.app_status_bar` | `KANDEV_FEATURES_APP_STATUS_BAR` | `false` in production | Opt-in global connection/host-metrics/plugin surface: bottom bar on tablet/desktop and Status drawer on phones. |
+| `features.claude_background_prompt_handoff` | `KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF` | `false` | High-risk experiment that lets Claude Code accept a new prompt after its foreground yields while adapter-attested background work remains active. Other providers keep the coarse busy gate. |
 
 Do not infer security from `auth.jwtSecret`: setting it currently does not turn the local server into an authenticated public service. Office's JWT key has a narrower, active purpose. Store both active secrets and third-party API keys in your deployment secret manager; never commit them in `config.yaml`.
 
@@ -294,11 +295,12 @@ Copying this entire file is unnecessary and can freeze old defaults in a deploym
 | `features.office` | `KANDEV_FEATURES_OFFICE` | off | Experimental autonomous-agent Office surfaces and automation. |
 | `features.plugins` | `KANDEV_FEATURES_PLUGINS` | off | Extensible plugin system: install/manage plugins and load their backends and native UI bundles. |
 | `features.appStatusBar` | `KANDEV_FEATURES_APP_STATUS_BAR` | off | Global status bar on tablet/desktop and Status drawer entry on phones. Enabling changes visibility only. |
+| `features.claudeBackgroundPromptHandoff` | `KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF` | off | High-risk Claude Code experiment that exposes recognized background-only activity and admits a successor prompt. |
 | `debug.devMode` | `KANDEV_DEBUG_DEV_MODE` (also locked by explicit legacy/debug-message vars) | off | High-risk diagnostic endpoints and ACP frame logging. |
 
 UI changes are persisted in the database and require a restart. An explicitly set environment value wins and locks the UI control. Otherwise a database override wins over the embedded profile/default. Resetting a toggle removes its database override.
 
-The source checkout's `make dev` activates the embedded development profile, which enables Office, debug surfaces, ACP logging, and a mock agent; the App status bar remains opt-in. Installed `run`/desktop builds select the safe production profile unless the environment explicitly opts in. E2E mock variables and routes are test-only and must never be enabled on a public deployment.
+The source checkout's `make dev` activates the embedded development profile, which enables Office, debug surfaces, ACP logging, and a mock agent; the App status bar and Claude background prompt handoff remain opt-in. Installed `run`/desktop builds select the safe production profile unless the environment explicitly opts in. E2E mock variables and routes are test-only and must never be enabled on a public deployment.
 
 ## Credentials and product settings
 
diff --git a/docs/public/feature-status.md b/docs/public/feature-status.md
index 8cb6a145b3..92939b4ae8 100644
--- a/docs/public/feature-status.md
+++ b/docs/public/feature-status.md
@@ -100,9 +100,10 @@ Released builds can lag this page. Check **Settings > System > About** or `kande
 | Statistics and host resource metrics                                            | Supported        | Workspace stats and on-demand CPU/memory/disk display are shipped. Execution-environment metrics depend on executor/runtime support.                                                                                                                                                                                                                         |
 | SQLite backups, database maintenance, status, and logs                          | Supported        | Backups use SQLite `VACUUM INTO` snapshots under the data root. Retention, free space, file permissions, and off-host copies remain operator responsibilities.                                                                                                                                                                                               |
 | Update checking and applying updates                                            | Dependency-bound | Checking is shipped. Package-manager installs update through their package manager; backend self-update is service-install-specific; desktop updater support varies by artifact/platform.                                                                                                                                                                    |
-| Feature Toggle settings                                                         | Supported        | The page exposes Office, Plugins, and Debug overrides, environment locks, and restart-required state. Debug is high risk because logs/endpoints can expose prompt, file, and tool data. A toggle being present does not promote its target feature to supported.                                                                                             |
+| Feature Toggle settings                                                         | Supported        | The page exposes Office, Plugins, Claude background prompt handoff, and Debug overrides, environment locks, and restart-required state. Claude background handoff and Debug are high risk. A toggle being present does not promote its target feature to supported.                                                                                        |
 | Office mode                                                                     | In progress      | Production defaults `KANDEV_FEATURES_OFFICE=false`; development and E2E enable it for implementation/testing. Its routes, agents, labels, documents, dependencies, routines, skills, routing, costs, and approvals may change between releases.                                                                                                              |
 | Plugin system                                                                   | In progress      | Production defaults `KANDEV_FEATURES_PLUGINS=false`; development and E2E enable it for implementation/testing. Loaded plugin code runs with backend privileges; manifest schema, capabilities, and host API may change between releases.                                                                                                                     |
+| Claude background prompt handoff                                                | Experimental     | Defaults `KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF=false` in every profile. When explicitly enabled, only Claude Code sessions can expose recognized background-only activity and accept a successor prompt. ACP lifecycle gaps can still misclassify activity or overlap prompts.                                                               |
 | Mock providers and E2E-only routes                                              | Internal         | They are selected only by development/test runtime profiles and must not be exposed as product integrations.                                                                                                                                                                                                                                                 |
 
 ## Publication boundary
diff --git a/docs/public/operations.md b/docs/public/operations.md
index 2f5f079938..3da7be6fe7 100644
--- a/docs/public/operations.md
+++ b/docs/public/operations.md
@@ -267,6 +267,7 @@ These metrics are lightweight UI observability. Set alerts, retention, CPU/memor
 
 - **Office mode** — experimental, medium risk, and off in the production profile by default.
 - **App status bar** — stable, low risk, and off in the production profile by default. Enabling it adds the desktop/tablet bar and phone Status entry after restart; disabling it again does not stop connections, metrics collection requested by other clients, or plugins.
+- **Claude background prompt handoff** — experimental, high risk, and off in every profile by default. Enabling it lets Claude Code accept another prompt after its foreground yields while recognized async subagent, `run_in_background` shell, or Monitor work remains active. ACP lifecycle gaps can misclassify activity or overlap prompts; use it only for controlled testing.
 - **Debug mode** — high risk; enables diagnostic endpoints and agent-message logging that can contain sensitive content.
 
 Each requires restart. A value supplied explicitly by its environment variable locks the UI control; the debug toggle is also locked by explicit legacy/debug-message environment variables. Otherwise the UI stores an override in the database. The page can request restart only when the native local supervisor is available. A normal Unix `kandev` terminal launch is supervised; Desktop, a service, a container, a directly started backend, a deploy preview, or Windows requires a manual application restart.
diff --git a/docs/public/sessions-and-review.md b/docs/public/sessions-and-review.md
index 60466f4f31..7610d888d6 100644
--- a/docs/public/sessions-and-review.md
+++ b/docs/public/sessions-and-review.md
@@ -144,7 +144,7 @@ Pending inline comments are scoped to the current review session but persist onl
 
 ## Generate a walkthrough
 
-Select **Walkthrough** from Changes or Review. Kandev sends the built-in `changes-walkthrough` prompt to the active session. If the agent is actively generating, the request queues; if it is idle — or only waiting on background work it spawned — it starts a new turn immediately. The agent must have task MCP and must call `show_walkthrough_kandev` with an ordered list of file and line anchors.
+Select **Walkthrough** from Changes or Review. Kandev sends the built-in `changes-walkthrough` prompt to the active session. If the agent is actively generating, the request queues; if it is idle, it starts a new turn immediately. A running Claude Code session that is only waiting on recognized background work also starts immediately when the high-risk **Claude background prompt handoff** experiment is enabled; the default behavior queues it. The agent must have task MCP and must call `show_walkthrough_kandev` with an ordered list of file and line anchors.
 
 <DocsVideo
   webm="./media/feature-guides/code-walkthrough.webm"
diff --git a/docs/public/tasks-and-workflows.md b/docs/public/tasks-and-workflows.md
index 81f32e30e2..4eab405470 100644
--- a/docs/public/tasks-and-workflows.md
+++ b/docs/public/tasks-and-workflows.md
@@ -133,13 +133,14 @@ A task created with **Create without starting agent** opens in a prepared workbe
 
 If the selected profile is unhealthy or incompatible with the executor, fix that configuration before launch. Starting an agent is separate from moving the task through its workflow; entry actions and turn-complete transitions can move or restart work afterward.
 
-When a session shows **Working in background**, its foreground turn has ended
-but recognized child work is still live. You can send a follow-up without
-waiting for that work to finish. Providers with an attested handoff, including
-Claude ACP, receive the follow-up immediately while the child may continue
-streaming. While the session still shows **Generating**, the provider retains
-foreground ownership and Kandev keeps another message queued until that
-ownership is released.
+By default, a running session keeps the coarse **Generating** state and queues
+another message even if Kandev detects background work. Operators can opt into
+the high-risk **Claude background prompt handoff** feature toggle for controlled
+testing. With that experiment enabled, a Claude Code session shows **Working in
+background** after its foreground yields while a recognized async subagent,
+`run_in_background` shell, or Monitor remains active. A follow-up is then sent
+immediately and the child may continue streaming. Other providers and
+foreground-generating Claude turns retain the coarse queueing behavior.
 
 ## Find and organize tasks
 
@@ -296,7 +297,11 @@ To restore a task, open **List**, enable **Show archived**, and choose unarchive
 
 Delete is permanent. If **Also delete _N_ subtasks** is left unchecked, direct children become root tasks. If selected, descendants are deleted. The operation cannot be undone, and executor cleanup follows the same asynchronous, best-effort rules as archive.
 
-When a task still has an agent generating or background work outstanding, the confirmation dialog adds a still-working warning: proceeding discards work that is in progress. Delete always shows this warning; archive shows it only when the archive confirmation is enabled.
+When a task still has a `RUNNING` agent, the confirmation dialog adds a
+still-working warning: proceeding discards work that is in progress. Delete
+always shows this warning; archive shows it only when the archive confirmation
+is enabled. Best-effort detached-work accounting does not independently keep a
+settled task in the still-working state.
 
 ## Troubleshooting
 
diff --git a/docs/public/websocket-api.md b/docs/public/websocket-api.md
index d880fec5d8..6c25c8b96c 100644
--- a/docs/public/websocket-api.md
+++ b/docs/public/websocket-api.md
@@ -702,14 +702,20 @@ system.job.update
 
 Current lifecycle code broadcasts `session.turn.started` and `session.turn.completed` globally even though their payloads identify a session. `task.subscribe` does not change this global routing.
 
-`session.activity_changed` carries `task_id`, `session_id`, `foreground_activity`,
-and `active_subagent_count`. The activity is `generating`, `background`, or
-`null`; the count is always an integer and is zero when no adapter-attested
-subagent is live for that session. Task lifecycle notifications expose the same count
-aggregated across
-the task's sessions as `active_subagent_count`. Count-only changes may emit
-`session.activity_changed` and `task.updated` even when the foreground activity
-and coarse lifecycle state do not change.
+`session.activity_changed` carries `task_id`, `session_id`,
+`foreground_activity`, and `active_subagent_count`. The activity is
+`generating` while the session is `RUNNING` and otherwise clears with the
+coarse lifecycle by default; background-work accounting does not expose a
+separate activity tier. When
+`KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF=true`, a persisted Claude
+Code session may instead expose `background` while its foreground has yielded
+and adapter-attested async subagent, background shell, or Monitor work remains
+active. Other providers remain coarse. The count is always an integer and is
+zero when no adapter-attested subagent is live for that session. Task lifecycle
+notifications expose the same count aggregated across the task's sessions as
+`active_subagent_count`. Count-only changes may emit
+`session.activity_changed` and `task.updated` even when the coarse lifecycle
+state does not change.
 
 Office workspace notifications are also global; clients filter on `workspace_id`:
 
diff --git a/docs/specs/platform/background-work-liveness.md b/docs/specs/platform/background-work-liveness.md
index 175cb96039..9feee215df 100644
--- a/docs/specs/platform/background-work-liveness.md
+++ b/docs/specs/platform/background-work-liveness.md
@@ -1,7 +1,7 @@
 ---
 status: shipped
 created: 2026-07-21
-updated: 2026-07-26
+updated: 2026-07-28
 owner: kandev
 ---
 
@@ -9,228 +9,125 @@ owner: kandev
 
 ## Why
 
-Operators need to know whether an agent is actively generating, is available
-for another prompt while recognized work continues, or has finished. Collapsing
-those conditions into a coarse running state both hides active background work
-and incorrectly prevents prompt delivery.
+ACP providers do not yet expose a consistent, accountable lifecycle for
+subagents and other background work. Kandev can account for recognized work,
+but that best-effort signal is not reliable enough to decide whether a
+`RUNNING` agent can safely receive another prompt by default. Prompt admission
+and operator-visible busy state therefore use the durable coarse session
+lifecycle unless a deployment deliberately enables the Claude-only experiment.
 
 ## What
 
-- A session distinguishes foreground generation from recognized background work.
-  Foreground activity takes precedence over background work; neither condition
-  may appear as done.
-- A foreground-idle session with recognized background work accepts a new
-  prompt. A session with foreground activity continues to reject it.
-- When a provider-attested, generation-bearing foreground-idle boundary also
-  guarantees prompt handoff, the next human prompt reaches the provider
-  immediately even if the prior prompt RPC remains open for detached work.
-  Synthetic wakeups remain serialized behind the owning RPC. Providers that do
-  not attest handoff keep the follow-up queued until they release ownership.
-- Only adapter-attested workloads relax prompt admission. An adapter opts in a
-  workload only when Kandev has fixture-tested both its launch and accountable
-  terminal lifecycle. Claude subagents, background shells, and Monitor watches
-  are initially supported. Codex and other ACP agents remain conservatively
-  foreground-busy until their providers reliably emit the terminal lifecycle
-  Kandev needs.
-- The runtime retains one registration per live subagent and derives an active
-  subagent count from those registrations. Background shells and Monitor
-  watches contribute to background liveness but not to the subagent count.
-- Task and session status surfaces distinguish generating,
-  background-running, and done with text or accessible labels in addition to
-  color. The compact sidebar uses the same dashed spinner for both running
-  states: yellow for foreground generation and violet for background work, with
-  a distinct background-work tooltip and accessible label. A pending
-  permission request takes precedence over a pending clarification request,
-  which in turn takes precedence over the work-state indicator for a current,
-  input-capable session only; stale pending flags on starting or terminal
-  sessions do not override the work-state indicator.
-- A task aggregates its sessions with most-active-wins: generating outranks
-  background-running, which outranks existing settled-state rendering.
-- A terminal asynchronous launch result closes its tool card but does not end
-  the launched workload. Work remains live until accountable completion or
-  execution teardown.
+- Every `RUNNING` session is busy, rejects direct prompt admission, and routes
+  composer input through the queued-message path by default.
+- Every `RUNNING` session is shown as generating. Background-work accounting
+  does not select a separate operator-visible activity tier by default.
+- A settled session follows its coarse state and does not remain visually busy
+  solely because detached work is still registered.
+- The runtime retains one registration per recognized live subagent and derives
+  `active_subagent_count` from those registrations. Background shells and
+  Monitor watches may remain internally tracked but do not contribute to the
+  subagent count.
+- Adapter attestation is accounting evidence only unless the
+  `features.claudeBackgroundPromptHandoff` experiment is enabled for a
+  `claude-acp` session.
+- When that experiment is enabled, all Claude modes covered by ADR-0049 retain
+  their fine-grained behavior: subagents, `run_in_background` shells, and
+  Monitor watches may expose background activity and a generation-matched
+  foreground handoff may admit the next prompt.
+- Non-Claude providers remain coarse even when the experiment is enabled.
+- The experiment is off in every embedded profile, high risk,
+  restart-required, and available through
+  `KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF`.
 - Terminal execution teardown retires every tool-ownership and background-work
   entry owned by that execution. It releases the whole session activity record
   when no successor execution or in-flight prompt/dispatch token still owns it.
-- The delete confirmation warns when a task has foreground or recognized
-  background work. Archive uses the same warning only when archive confirmation
-  is enabled.
 
 ## API surface
 
-- Session records and boot payloads expose `foreground_activity` as
-  `generating`, `background`, or absent when no fine-grained activity is known.
-  `background` can be present after the coarse session state settles.
+- A `RUNNING` session record, boot payload, activity notification, or state
+  notification exposes `foreground_activity=generating` by default. An
+  eligible session in the enabled Claude experiment may expose `background`.
+- Settled session records omit `foreground_activity`; task records aggregate
+  only coarse running activity.
+- `session.activity_changed` carries `task_id`, `session_id`,
+  `foreground_activity`, and `active_subagent_count`. Its activity is
+  `generating` while the session is running; count-only changes may publish
+  without an activity-tier change.
 - Session records, boot payloads, activity/state notifications, task records,
-  and `task.updated` always expose `active_subagent_count` as an integer. It is
-  zero when no adapter-attested subagent is live and may be positive while
-  `foreground_activity` is either `generating` or `background`.
-- `session.activity_changed` publishes the changed fine-grained session value
-  and active subagent count; a count-only transition is publishable even when
-  the activity tier does not change. `session.state_changed` carries both with
-  coarse state changes.
-- Task records and `task.updated` carry the most-active-wins
-  `foreground_activity` aggregate and the sum of active subagents across its
-  sessions. A task update is emitted when either aggregate changes, including a
-  generating-to-background or count-only transition with no coarse state
-  change.
+  and `task.updated` expose `active_subagent_count` as an integer. It is zero
+  when no adapter-attested subagent is live.
 
 ## State machine
 
-| State | Entry | Exit |
+| Coarse state | Prompt admission | Operator activity |
 | --- | --- | --- |
-| generating | A prompt is claimed or dispatched, or known top-level foreground work emits output. | The current prompt yields or completes, unless more foreground activity arrives. |
-| background-running | The foreground is idle and one or more recognized workloads remain registered. | A foreground prompt/output takes precedence, or the final workload completes or is torn down. |
-| idle/done | Neither foreground ownership nor recognized background work remains. | A foreground prompt/output or recognized workload begins. |
+| `RUNNING` | Queue/reject by default; enabled Claude handoff may accept | generating by default; enabled Claude may show background |
+| `WAITING_FOR_INPUT`, `COMPLETED`, or `IDLE` | Accept | omitted |
+| `STARTING`, `CREATED`, `FAILED`, or `CANCELLED` | Reject as not promptable | omitted |
 
-Prompt admission is atomic: only one prompt can claim foreground ownership for
-a session. Delayed release or completion from an earlier prompt cycle cannot
-mutate a later accepted claim. Prompt delivery is serialized per agent
-execution except for one generation-matched human ownership transfer at an
-adapter-attested provider handoff. The transfer finalizes the earlier lifecycle
-buffer/completion owner before the successor starts; synthetic wakeups cannot
-consume it, and a delayed response from the earlier RPC cannot finalize the
-successor. Prompt-end cleanup for that successor excludes predecessor background
-work and its nested tool/Monitor lineage, while explicit cancellation and session
-replacement still clear all ownership.
+The background-work tracker may still transition internally between foreground
+ownership and recognized background liveness. Those transitions do not change
+the table above.
 
 ## Failure modes
 
-- An unknown activity value for an in-flight `RUNNING` session is rendered as
-  generating, not done.
-- A foreground-idle signal without a nonzero matching prompt generation and
-  adapter-attested handoff capability does not relax transport serialization.
-  The session remains visibly foreground-owned and the follow-up remains
-  queued rather than being reported as delivered.
-- A normalized tool-card shape cannot attest to background capability. An
-  unsupported adapter that emits a subagent-looking card remains foreground-busy
-  until its launch, yield, and terminal lifecycle are explicitly supported.
-- The development/E2E mock provider may replay captured Claude lifecycle
-  metadata through the same attested path. This is a deterministic test seam,
-  not an additional production-agent capability.
-- Codex child thread/session identity may correlate launch and activity cards
-  for presentation, but Codex subagents do not attest background liveness.
-  Observed Codex ACP streams can omit accountable terminal child activity, so a
-  started card must not create a live registration or nonzero subagent count.
-- Tool-call ownership is established by the initial call and retained across
-  incremental updates from the same execution. Ownership includes the execution
-  identity because provider-local tool-call IDs may be reused after rotation.
-  An update with unknown ownership preserves the current activity; missing
-  parent metadata is not evidence that background-child work became foreground
-  work.
-- A task aggregate that cannot be recomputed preserves its last-known value
-  rather than publishing a spurious done reading.
-- When provider completion identifies a workload, only that registration is
-  retired; duplicate completion is harmless. An uncorrelated completion retires
-  only one outstanding registration and leaves an ambiguous remainder live.
+- With the experiment off, missing, delayed, duplicated, or provider-specific
+  background lifecycle frames cannot make a `RUNNING` session promptable.
+- With the experiment on, only adapter-attested Claude lifecycle frames can
+  relax the gate. Missing provider identity and every non-Claude provider fail
+  closed.
+- A normalized tool-card shape cannot attest to promptability.
+- Codex child thread/session identity and Claude task notifications may be used
+  for presentation or accounting, but neither changes the coarse admission
+  rule.
+- Count drift is prevented by deriving `active_subagent_count` from the live
+  registration map rather than maintaining an independent counter.
 - Execution completion, stop, failure, cancellation, crash cleanup, forced
-  cleanup, and session removal retire all activity owned by that execution.
-  Cleanup is idempotent and must preserve activity already claimed by a
-  successor on the same session. Session removal quiesces any still-live
-  lifecycle execution and rejects deletion if that stop fails, except when the
-  runtime reports that the exact execution is already absent. Per-session
-  activity validation and delivery remain ordered across record replacement;
-  each publication snapshots its activity value and active-subagent count
-  together. Per-task publication is FIFO: a newly computed activity value must
-  not be published ahead of an earlier value for the same task, and a detached
-  predecessor record or stale publication must not overwrite a newer session or
-  task aggregate.
+  cleanup, and session removal retire activity owned by that execution.
 
 ## Persistence guarantees
 
-Fine-grained activity is in memory and is authoritative only while the owning
-agent execution remains connected. A backend or agent-execution restart does
-not reconstruct detached work or active subagent counts; it must not preserve a
-stale live reading. Counts are derived from the live registration map rather
-than persisted or incremented independently. Execution teardown releases the
-record when it has no successor owner; completed session history does not retain
-an empty activity record. Durable coarse state continues to survive as before.
+Background-work accounting is in memory and authoritative only while the owning
+agent execution remains connected. A restart does not reconstruct detached work
+or active subagent counts. Durable coarse session state remains the source of
+truth for prompt admission and operator-visible activity.
 
 ## Scenarios
 
-- **GIVEN** a foreground-idle session with a recognized background workload,
-  **WHEN** the operator sends a prompt, **THEN** the prompt is accepted while
-  the status remains background-running until foreground activity begins.
-- **GIVEN** an attested provider keeps a prompt RPC open for a detached child
-  after emitting foreground-idle for the matching generation, **WHEN** the
-  operator sends a follow-up, **THEN** that human prompt reaches the provider
-  immediately and the detached child may continue streaming.
-- **GIVEN** a synthetic wakeup is waiting when an attested human handoff occurs,
-  **WHEN** a human follow-up is submitted, **THEN** the human prompt inherits
-  ownership and the wakeup remains serialized until the human turn completes.
-- **GIVEN** predecessor background tools or Monitors are still live after the
-  follow-up completes, **WHEN** the successor runs prompt-end cleanup, **THEN**
-  those predecessor-owned streams remain tracked until their authoritative
-  terminal event, explicit cancellation, or session replacement.
-- **GIVEN** the provider has not authoritatively released the foreground,
-  **WHEN** the operator submits a follow-up, **THEN** Kandev reports it as
-  queued and does not send it concurrently.
+- **GIVEN** the experiment is off and a `RUNNING` session's tracker reports
+  foreground-idle with recognized background work, **WHEN** the operator
+  submits a prompt, **THEN** Kandev queues it.
+- **GIVEN** the experiment is on for a `claude-acp` session and its tracker
+  reports adapter-attested background work plus a generation-matched foreground
+  handoff, **WHEN** the operator submits a prompt, **THEN** Kandev dispatches the
+  successor without queueing it.
+- **GIVEN** the experiment is on for any non-Claude provider, **WHEN** the same
+  tracker-shaped activity is observed, **THEN** Kandev still queues the prompt.
+- **GIVEN** the same session is rendered or freshly reloaded, **WHEN** its
+  activity is serialized, **THEN** it is shown as generating rather than
+  background-running.
 - **GIVEN** two adapter-attested subagents and one background shell are live,
-  **WHEN** the session is serialized or publishes an activity update, **THEN**
-  `active_subagent_count` is two while all three workloads still contribute to
-  background liveness.
-- **GIVEN** one generating session with one live subagent and another session
-  with two live subagents, **WHEN** the task is serialized, **THEN** its
-  `foreground_activity` is generating and its `active_subagent_count` is three.
-- **GIVEN** a Codex subagent launch card without an accountable terminal
-  lifecycle, **WHEN** its prompt remains in flight or later settles, **THEN**
-  Kandev may render the card but reports no recognized background work and the
-  active subagent count remains zero.
-- **GIVEN** an unsupported ACP adapter emits a normalized subagent-shaped tool
-  card, **WHEN** its prompt remains in flight, **THEN** Kandev reports the
-  foreground as generating and the active subagent count remains zero.
-- **GIVEN** a task with one generating session and one background-running
-  session, **WHEN** its aggregate is rendered, **THEN** it shows generating.
-- **GIVEN** a task with no generating session and one background-running
-  session, **WHEN** its aggregate is rendered on a board, list, graph, header,
-  or sidebar, **THEN** it does not show done.
-- **GIVEN** a detached workload launch completes, **WHEN** no workload terminal
-  signal has arrived, **THEN** the session stays background-running.
-- **GIVEN** a child tool call was attributed to recognized background work,
-  **WHEN** an incremental update temporarily omits its parent metadata,
-  **THEN** the session remains background-running.
-- **GIVEN** a freshly loaded page or a second browser tab, **WHEN** a connected
-  session has current background activity, **THEN** its task and session
-  surfaces show background-running without waiting for a transition.
-- **GIVEN** an activity transition for a task, **WHEN** a later transition is
-  computed before earlier publication completes, **THEN** observers never see
-  the later value followed by the stale earlier value.
+  **WHEN** activity is serialized, **THEN** `active_subagent_count` is two while
+  the session's operator activity still follows its coarse state.
+- **GIVEN** the session leaves `RUNNING`, **WHEN** its DTO or task aggregate is
+  serialized, **THEN** foreground activity is omitted even if detached work
+  remains registered.
 - **GIVEN** an execution terminates with orphaned tool ownership and background
-  work and no successor exists, **WHEN** teardown runs, **THEN** all owned state
-  and the session activity record are released.
-- **GIVEN** execution B has claimed the same session before delayed teardown for
-  execution A, **WHEN** A is retired, **THEN** B's prompt claim, prompt
-  generation, foreground state, tools, and background work remain unchanged.
-- **GIVEN** execution B reuses a tool-call ID left nonterminal by execution A,
-  **WHEN** B emits an ownership-incomplete update, **THEN** A's classification
-  is not observable as ownership evidence for B.
-- **GIVEN** execution A's cleanup publication is delayed until after execution B
-  claims the session, **WHEN** the delayed publication resumes, **THEN** it
-  cannot recreate A's record or overwrite B's activity.
-- **GIVEN** a task with active foreground or recognized background work,
-  **WHEN** the operator deletes it, **THEN** the confirmation warns that work is
-  still in progress.
-- **GIVEN** a task with active foreground or recognized background work,
-  **WHEN** the operator archives it with archive confirmation enabled, **THEN**
-  the archive confirmation carries the same warning.
-- **GIVEN** archive confirmation is disabled, **WHEN** the operator archives a
-  task with active foreground or recognized background work, **THEN** no archive
-  dialog is shown.
+  work, **WHEN** teardown runs, **THEN** its owned accounting state is released.
 
 ## Out of scope
 
 - Mid-turn steering for agents without concurrent-prompt capability.
-- Reconstructing detached-work liveness after backend or agent-execution
-  restart.
-- Rendering the active subagent count or individual subagent details in the UI.
-- Changing Office autonomous-agent status vocabulary.
-- Changing archive behavior when the operator has disabled archive
-  confirmation.
+- Reconstructing detached-work liveness after restart.
+- Rendering active subagent counts or individual subagent details in the UI.
 
 ## Decision record
 
-[ADR 0049 — Fine-grained foreground-idle busy signal](../../decisions/0049-fine-grained-foreground-idle-busy-signal.md) owns the architectural reasoning: ownership and admission rules, provider attestation, and the per-task publication-order invariant.
+[ADR-2026-07-28 — Restore Coarse Running Prompt Admission](../../decisions/2026-07-28-coarse-running-busy-signal.md)
+supersedes the operator policy in
+[ADR 0049 — Fine-grained foreground-idle busy signal](../../decisions/0049-fine-grained-foreground-idle-busy-signal.md).
 
 ## Implementation plan
 
-[Background work liveness implementation plan](../../plans/background-work-liveness/plan.md)
+[Coarse running busy signal fix plan](../../plans/coarse-running-busy-signal/plan.md)