diff --git a/apps/backend/internal/backendapp/main.go b/apps/backend/internal/backendapp/main.go
index a376a77951..9b8390c684 100644
--- a/apps/backend/internal/backendapp/main.go
+++ b/apps/backend/internal/backendapp/main.go
@@ -1276,6 +1276,7 @@ func initOfficeServices(
 		agentRegistry, log, services, cfg.Office.JWTSigningKey,
 	)
 	wireOfficeSvcsDependencies(services, repos, eventBus, orchestratorSvc, agentRegistry)
+	services.OfficeSvcs.Dashboard.SetOfficeSessionIdentity(cfg.Features.OfficeSessionIdentity)
 
 	// Reconcile using the new infra package.
 	reconciler := officeinfra.NewReconciler(repos.Office, log)
diff --git a/apps/backend/internal/backendapp/orchestrator.go b/apps/backend/internal/backendapp/orchestrator.go
index 7ee4686ea3..887715dbb9 100644
--- a/apps/backend/internal/backendapp/orchestrator.go
+++ b/apps/backend/internal/backendapp/orchestrator.go
@@ -82,6 +82,8 @@ func provideOrchestrator(
 		cfg != nil && cfg.Features.ClaudeBackgroundPromptHandoff
 	serviceCfg.ClaudeMidTurnSteering =
 		cfg != nil && cfg.Features.ClaudeMidTurnSteering
+	serviceCfg.OfficeSessionIdentity =
+		cfg != nil && cfg.Features.OfficeSessionIdentity
 	namespace := resolveEventNamespace(cfg)
 	serviceCfg.QueueGroup = "orchestrator." + namespace
 	busMode := "memory"
diff --git a/apps/backend/internal/common/config/catalog.go b/apps/backend/internal/common/config/catalog.go
index f5cb5e9137..776760d5fc 100644
--- a/apps/backend/internal/common/config/catalog.go
+++ b/apps/backend/internal/common/config/catalog.go
@@ -130,6 +130,7 @@ var startupExclusions = []CatalogExclusion{
 	{EnvVar: "KANDEV_FEATURES_AUTH", Class: "profile", Reason: "runtime feature flag registry"},
 	{EnvVar: "KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF", Class: "debug", Reason: "runtime feature flag registry"},
 	{EnvVar: "KANDEV_FEATURES_CLAUDE_MID_TURN_STEERING", Class: "debug", Reason: "runtime feature flag registry"},
+	{EnvVar: "KANDEV_FEATURES_OFFICE_SESSION_IDENTITY", Class: "debug", Reason: "runtime feature flag registry"},
 	{EnvVar: "KANDEV_DEBUG_AGENT_MESSAGES", Class: "debug", Reason: "ACP frame diagnostics"},
 	{EnvVar: "KANDEV_DEBUG_ACP_MAX_FILES", Class: "debug", Reason: "ACP debug retention"},
 	{EnvVar: "KANDEV_DEBUG_ACP_RETENTION_HOURS", Class: "debug", Reason: "ACP debug retention"},
diff --git a/apps/backend/internal/common/config/catalog_test.go b/apps/backend/internal/common/config/catalog_test.go
index 2599933db1..a729fe4464 100644
--- a/apps/backend/internal/common/config/catalog_test.go
+++ b/apps/backend/internal/common/config/catalog_test.go
@@ -150,6 +150,7 @@ func auditedStartupEnvironmentInventory() []auditedStartupEnvironment {
 		{envVar: "KANDEV_FEATURES_AUTH", class: "exclusion"},
 		{envVar: "KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF", class: "exclusion"},
 		{envVar: "KANDEV_FEATURES_CLAUDE_MID_TURN_STEERING", class: "exclusion"},
+		{envVar: "KANDEV_FEATURES_OFFICE_SESSION_IDENTITY", class: "exclusion"},
 		{envVar: "KANDEV_DEBUG_AGENT_MESSAGES", class: "exclusion"},
 		{envVar: "KANDEV_DEBUG_ACP_MAX_FILES", class: "exclusion"},
 		{envVar: "KANDEV_DEBUG_ACP_RETENTION_HOURS", class: "exclusion"},
diff --git a/apps/backend/internal/common/config/config.go b/apps/backend/internal/common/config/config.go
index c44f3bdd69..2c4039c07b 100644
--- a/apps/backend/internal/common/config/config.go
+++ b/apps/backend/internal/common/config/config.go
@@ -461,6 +461,14 @@ type FeaturesConfig struct {
 	// kill-switch after rollout because the agent-side fold is undocumented and
 	// can regress without notice.
 	ClaudeMidTurnSteering bool `mapstructure:"claude_mid_turn_steering" json:"claudeMidTurnSteering"`
+
+	// OfficeSessionIdentity keys an Office task's session identity on the run's
+	// own agent instead of the task's runner seat, and binds an agent's
+	// decision re-evaluation to its own calling session instead of the task's
+	// most-recently-started session. Off in every embedded profile: enabling it
+	// exposes pre-existing duplicate (task_id, agent_profile_id) rows until the
+	// companion unique-index fix has shipped.
+	OfficeSessionIdentity bool `mapstructure:"office_session_identity" json:"officeSessionIdentity"`
 }
 
 // LoggingConfig holds logging configuration.
diff --git a/apps/backend/internal/mcp/handlers/agent_decision_handlers.go b/apps/backend/internal/mcp/handlers/agent_decision_handlers.go
index d68cc97516..68fb5e66b9 100644
--- a/apps/backend/internal/mcp/handlers/agent_decision_handlers.go
+++ b/apps/backend/internal/mcp/handlers/agent_decision_handlers.go
@@ -63,6 +63,7 @@ func (h *Handlers) handleRecordStepDecision(ctx context.Context, msg *ws.Message
 		AgentProfileID: session.AgentProfileID,
 		Decision:       req.Decision,
 		Reason:         req.Reason,
+		SessionID:      req.SessionID,
 	})
 	if err != nil {
 		if !errors.Is(err, shared.ErrForbidden) && !dashboard.IsAgentDecisionValidationError(err) {
diff --git a/apps/backend/internal/office/dashboard/agent_decisions.go b/apps/backend/internal/office/dashboard/agent_decisions.go
index 5b2a00659c..3108360b7a 100644
--- a/apps/backend/internal/office/dashboard/agent_decisions.go
+++ b/apps/backend/internal/office/dashboard/agent_decisions.go
@@ -25,6 +25,13 @@ type RecordAgentDecisionInput struct {
 	AgentProfileID string
 	Decision       string
 	Reason         string
+	// SessionID, when features.officeSessionIdentity is on, names the
+	// decider's own calling session so RecordDecision re-evaluates against
+	// it instead of the task's most-recently-started ("active") session.
+	// Populated unconditionally by the MCP handler; gated here because the
+	// flag decision belongs with the rest of this service's behavior, not
+	// the transport layer.
+	SessionID string
 }
 
 // AgentDecisionValidationError marks an error caused by a caller-provided
@@ -137,7 +144,7 @@ func (s *DashboardService) RecordAgentDecision(
 		return nil, agentDecisionValidation(fmt.Errorf("%s", agentDecisionReasonRequiredErr))
 	}
 
-	result, err := dispatcher.RecordDecision(ctx, officeenginedispatcher.RecordDecisionInput{
+	decisionInput := officeenginedispatcher.RecordDecisionInput{
 		TaskID:        in.TaskID,
 		StepID:        stepID,
 		ParticipantID: participantID,
@@ -146,7 +153,11 @@ func (s *DashboardService) RecordAgentDecision(
 		DeciderID:     in.AgentProfileID,
 		Role:          role,
 		Comment:       in.Reason,
-	})
+	}
+	if s.officeSessionIdentity {
+		decisionInput.SessionID = in.SessionID
+	}
+	result, err := dispatcher.RecordDecision(ctx, decisionInput)
 	if err != nil {
 		return nil, fmt.Errorf("record decision: %w", err)
 	}
diff --git a/apps/backend/internal/office/dashboard/agent_decisions_test.go b/apps/backend/internal/office/dashboard/agent_decisions_test.go
index dcf4acec6d..f91a0a3ebf 100644
--- a/apps/backend/internal/office/dashboard/agent_decisions_test.go
+++ b/apps/backend/internal/office/dashboard/agent_decisions_test.go
@@ -6,11 +6,106 @@ import (
 	"testing"
 
 	"github.com/kandev/kandev/internal/office/dashboard"
+	officeenginedispatcher "github.com/kandev/kandev/internal/office/engine_dispatcher"
 	"github.com/kandev/kandev/internal/office/models"
 	"github.com/kandev/kandev/internal/office/shared"
 	"github.com/kandev/kandev/internal/workflow/engine"
 )
 
+// spyDecisionDispatcher satisfies shared.WorkflowEngineDispatcher plus the
+// package-local decisionRecordingDispatcher/roleResolvingDispatcher/
+// quorumEvaluatingDispatcher capabilities RecordAgentDecision reaches via
+// type assertion (all exported methods, so a type from this external test
+// package can still satisfy those unexported interfaces structurally).
+// Unlike newTestEngineDispatcher's real engine, this spy captures the exact
+// RecordDecisionInput it was called with, so a test can assert whether
+// SessionID was forwarded without needing a live session row to observe an
+// engine-side behavior difference.
+type spyDecisionDispatcher struct {
+	role          string
+	participantID string
+	lastInput     officeenginedispatcher.RecordDecisionInput
+}
+
+func (s *spyDecisionDispatcher) HandleTrigger(
+	_ context.Context, _ string, _ engine.Trigger, _ any, _ string,
+) error {
+	return nil
+}
+
+func (s *spyDecisionDispatcher) ResolveParticipantRole(
+	_ context.Context, _, _, _ string,
+) (string, string, error) {
+	return s.role, s.participantID, nil
+}
+
+func (s *spyDecisionDispatcher) RecordDecision(
+	_ context.Context, in officeenginedispatcher.RecordDecisionInput,
+) (officeenginedispatcher.RecordDecisionResult, error) {
+	s.lastInput = in
+	return officeenginedispatcher.RecordDecisionResult{DecisionID: "decision-spy"}, nil
+}
+
+func (s *spyDecisionDispatcher) EvaluateStepQuorum(
+	_ context.Context, _ string,
+) (engine.QuorumSnapshot, error) {
+	return engine.QuorumSnapshot{}, nil
+}
+
+// TestRecordAgentDecision_SessionIDNotForwardedWhenFlagOff is the default
+// (flag-off) case: even though the caller supplies a SessionID, the
+// dispatcher never sees it, so RecordDecision falls back to its existing
+// resolveActiveSessionID path — the pre-office-session-identity behavior.
+func TestRecordAgentDecision_SessionIDNotForwardedWhenFlagOff(t *testing.T) {
+	deps := newTestDeps(t)
+	insertTestTask(t, deps.db, "sid1", "ws-d", "SID1", "in_review", 2)
+	mustAddParticipant(t, deps, "sid1", "agent-1", models.ParticipantRoleApprover)
+	spy := &spyDecisionDispatcher{role: models.ParticipantRoleApprover, participantID: "participant-1"}
+	deps.svc.SetWorkflowEngineDispatcher(spy)
+
+	_, err := deps.svc.RecordAgentDecision(context.Background(), dashboard.RecordAgentDecisionInput{
+		TaskID:         "sid1",
+		AgentProfileID: "agent-1",
+		Decision:       engine.DecisionApproved,
+		Reason:         "lgtm",
+		SessionID:      "sess-caller",
+	})
+	if err != nil {
+		t.Fatalf("RecordAgentDecision: %v", err)
+	}
+	if spy.lastInput.SessionID != "" {
+		t.Errorf("SessionID = %q, want blank (flag is off)", spy.lastInput.SessionID)
+	}
+}
+
+// TestRecordAgentDecision_SessionIDForwardedWhenFlagOn proves that once
+// features.officeSessionIdentity is enabled, RecordAgentDecision forwards
+// the caller's own SessionID into RecordDecisionInput, so RecordDecision
+// re-evaluates against the decider's own session instead of the task's
+// most-recently-started ("active") one.
+func TestRecordAgentDecision_SessionIDForwardedWhenFlagOn(t *testing.T) {
+	deps := newTestDeps(t)
+	insertTestTask(t, deps.db, "sid2", "ws-d", "SID2", "in_review", 2)
+	mustAddParticipant(t, deps, "sid2", "agent-1", models.ParticipantRoleApprover)
+	spy := &spyDecisionDispatcher{role: models.ParticipantRoleApprover, participantID: "participant-1"}
+	deps.svc.SetWorkflowEngineDispatcher(spy)
+	deps.svc.SetOfficeSessionIdentity(true)
+
+	_, err := deps.svc.RecordAgentDecision(context.Background(), dashboard.RecordAgentDecisionInput{
+		TaskID:         "sid2",
+		AgentProfileID: "agent-1",
+		Decision:       engine.DecisionApproved,
+		Reason:         "lgtm",
+		SessionID:      "sess-caller",
+	})
+	if err != nil {
+		t.Fatalf("RecordAgentDecision: %v", err)
+	}
+	if spy.lastInput.SessionID != "sess-caller" {
+		t.Errorf("SessionID = %q, want sess-caller (flag is on)", spy.lastInput.SessionID)
+	}
+}
+
 // insertTestTaskNoStep inserts a task row with no workflow_step_id bound
 // (the schema default is ” — see tasks.workflow_step_id NOT NULL DEFAULT
 // ”), exercising the AC-7/AC-55(1) precondition RecordAgentDecision must
diff --git a/apps/backend/internal/office/dashboard/service.go b/apps/backend/internal/office/dashboard/service.go
index 39a8d655ac..ce113acc6d 100644
--- a/apps/backend/internal/office/dashboard/service.go
+++ b/apps/backend/internal/office/dashboard/service.go
@@ -361,6 +361,18 @@ type DashboardService struct {
 	routingProvider  RoutingProvider                 // optional; nil disables /routing endpoints (503)
 	attemptLister    RouteAttemptLister              // optional; nil disables attempt embedding on run-detail responses
 	runResolver      RunResolver                     // optional; nil means status-change activity rows have no run_id
+	// officeSessionIdentity gates RecordAgentDecision's use of the caller's
+	// own session id. Defaults false (zero value); set via
+	// SetOfficeSessionIdentity, wired from features.officeSessionIdentity.
+	officeSessionIdentity bool
+}
+
+// SetOfficeSessionIdentity wires the features.officeSessionIdentity flag.
+// When true, RecordAgentDecision forwards the decider's own calling session
+// id so RecordDecision re-evaluates against it instead of the task's
+// most-recently-started ("active") session. Defaults false.
+func (s *DashboardService) SetOfficeSessionIdentity(enabled bool) {
+	s.officeSessionIdentity = enabled
 }
 
 // SetRoutingProvider wires the provider-routing seam used by the
diff --git a/apps/backend/internal/office/engine_dispatcher/dispatcher.go b/apps/backend/internal/office/engine_dispatcher/dispatcher.go
index 878f919d85..426bf8494f 100644
--- a/apps/backend/internal/office/engine_dispatcher/dispatcher.go
+++ b/apps/backend/internal/office/engine_dispatcher/dispatcher.go
@@ -74,6 +74,15 @@ type RecordDecisionInput struct {
 	DeciderID     string
 	Role          string
 	Comment       string
+	// SessionID, when non-empty, names the decider's own calling session.
+	// RecordDecision re-evaluates against this session instead of the
+	// task's most-recently-started ("active") session, so a reviewer/
+	// approver's decision is checked against the seats their own session
+	// occupies rather than whichever session happens to be newest.
+	// Callers only populate this behind features.officeSessionIdentity
+	// (see office/dashboard.DashboardService.SetOfficeSessionIdentity);
+	// leaving it empty preserves the existing resolveActiveSessionID path.
+	SessionID string
 }
 
 // RecordDecisionResult mirrors engine.RecordDecisionResult plus the
@@ -270,9 +279,15 @@ func (d *Dispatcher) RecordDecision(ctx context.Context, in RecordDecisionInput)
 	if in.TaskID == "" {
 		return RecordDecisionResult{}, fmt.Errorf("task_id is required")
 	}
-	sessionID, err := d.resolveActiveSessionID(ctx, in.TaskID)
+	var sessionID string
+	var err error
+	if in.SessionID != "" {
+		sessionID, err = d.resolveDeciderSessionID(ctx, in.TaskID, in.SessionID)
+	} else {
+		sessionID, err = d.resolveActiveSessionID(ctx, in.TaskID)
+	}
 	if err != nil {
-		return RecordDecisionResult{}, fmt.Errorf("resolve active session: %w", err)
+		return RecordDecisionResult{}, fmt.Errorf("resolve decider session: %w", err)
 	}
 	result, err := d.engine.RecordParticipantDecision(ctx, sessionID, engine.DecisionInfo{
 		TaskID:        in.TaskID,
@@ -368,9 +383,66 @@ func (d *Dispatcher) resolveActiveSessionID(ctx context.Context, taskID string)
 	return session.ID, nil
 }
 
+// resolveDeciderSessionID validates the decider's own calling session
+// (RecordDecisionInput.SessionID) rather than resolving the task's active
+// session. It returns "" (session_unresolvable, not an error) when the
+// session is missing, belongs to a different task, or is not in one of the
+// active states — mirroring resolveActiveSessionID's own never-an-error
+// contract for "no session resolvable" (AC-16a) — so a stale or foreign
+// session id degrades to the same "skip re-evaluation" behavior an
+// unresolvable active session already gets, rather than rejecting the
+// decision outright.
+//
+// The active-state set mirrors GetActiveTaskSessionByTaskID's own query
+// (internal/task/repository/sqlite/session.go) — there is no shared
+// models-level predicate for that set, so this local copy must be kept in
+// sync with it.
+func (d *Dispatcher) resolveDeciderSessionID(ctx context.Context, taskID, sessionID string) (string, error) {
+	session, err := d.sessions.GetTaskSession(ctx, sessionID)
+	if err != nil {
+		if errors.Is(err, taskmodels.ErrTaskSessionNotFound) {
+			d.logSessionUnresolvable(taskID, sessionID, "not_found")
+			return "", nil
+		}
+		return "", err
+	}
+	if session == nil || session.TaskID != taskID {
+		d.logSessionUnresolvable(taskID, sessionID, "foreign")
+		return "", nil
+	}
+	if !isActiveSessionState(session.State) {
+		d.logSessionUnresolvable(taskID, sessionID, "terminal")
+		return "", nil
+	}
+	return session.ID, nil
+}
+
+func (d *Dispatcher) logSessionUnresolvable(taskID, sessionID, reason string) {
+	d.logger.Debug("resolveDeciderSessionID: session unresolvable, falling back to blank",
+		zap.String("task_id", taskID),
+		zap.String("supplied_session_id", sessionID),
+		zap.String("reason", reason))
+}
+
+func isActiveSessionState(state taskmodels.TaskSessionState) bool {
+	switch state {
+	case taskmodels.TaskSessionStateCreated,
+		taskmodels.TaskSessionStateStarting,
+		taskmodels.TaskSessionStateRunning,
+		taskmodels.TaskSessionStateWaitingForInput:
+		return true
+	default:
+		return false
+	}
+}
+
 // resolveLatestSessionID returns the F38 "any session" id (the task's
 // most recent session regardless of state), or "" when the task has never
-// had one.
+// had one. Like resolveActiveSessionID and resolveDeciderSessionID, this is
+// scoped to the given taskID — GetTaskSessionByTaskID's own query already
+// filters by task, so unlike resolveDeciderSessionID (which validates a
+// caller-supplied session id and must check task ownership itself), there
+// is no cross-task session id to smuggle in here.
 func (d *Dispatcher) resolveLatestSessionID(ctx context.Context, taskID string) (string, error) {
 	session, err := d.sessions.GetTaskSessionByTaskID(ctx, taskID)
 	if err != nil {
diff --git a/apps/backend/internal/office/engine_dispatcher/dispatcher_decisions_test.go b/apps/backend/internal/office/engine_dispatcher/dispatcher_decisions_test.go
index a4ae419795..3b500cfb6b 100644
--- a/apps/backend/internal/office/engine_dispatcher/dispatcher_decisions_test.go
+++ b/apps/backend/internal/office/engine_dispatcher/dispatcher_decisions_test.go
@@ -302,3 +302,129 @@ func TestDispatcher_EvaluateStepQuorum_PropagatesEngineError(t *testing.T) {
 		t.Fatalf("err = %v, want wrapped engine error", err)
 	}
 }
+
+// TestDispatcher_RecordDecision_UsesSuppliedSessionOverActiveSession is the
+// office-session-identity happy path: when RecordDecisionInput.SessionID is
+// populated, the dispatcher resolves and forwards THAT session rather than
+// the task's most-recently-started ("active") session — even when the two
+// differ, proving the decider's own session wins.
+func TestDispatcher_RecordDecision_UsesSuppliedSessionOverActiveSession(t *testing.T) {
+	eng := &fakeEngine{decisionResult: engine.RecordDecisionResult{DecisionID: "decision-1"}}
+	sessions := &fakeSessions{
+		// The "active" (most-recently-started) session is a different one
+		// than the decider's own — proves SessionID, not activeSession, wins.
+		activeSession: &taskmodels.TaskSession{ID: "sess-runner"},
+		byID: map[string]*taskmodels.TaskSession{
+			"sess-reviewer": {ID: "sess-reviewer", TaskID: "task-1", State: taskmodels.TaskSessionStateRunning},
+		},
+	}
+	d := New(eng, sessions, logger.Default())
+
+	_, err := d.RecordDecision(context.Background(), RecordDecisionInput{
+		TaskID: "task-1", StepID: "review", ParticipantID: "participant-1",
+		Decision: "approved", SessionID: "sess-reviewer",
+	})
+	if err != nil {
+		t.Fatalf("RecordDecision: %v", err)
+	}
+	if eng.decisionSession != "sess-reviewer" {
+		t.Errorf("session id = %q, want sess-reviewer (decider's own session, not the active one)", eng.decisionSession)
+	}
+}
+
+// TestDispatcher_RecordDecision_ForeignSessionFallsBackToUnresolvable
+// covers the "session_unresolvable, not an error" contract: a supplied
+// session that belongs to a different task must not leak cross-task state
+// into re-evaluation, but must also not fail the decision outright — it
+// degrades to the same blank-session-id "skip re-evaluation" behavior
+// AC-16a already gives an unresolvable active session.
+func TestDispatcher_RecordDecision_ForeignSessionFallsBackToUnresolvable(t *testing.T) {
+	eng := &fakeEngine{decisionResult: engine.RecordDecisionResult{DecisionID: "decision-1"}}
+	sessions := &fakeSessions{
+		byID: map[string]*taskmodels.TaskSession{
+			"sess-foreign": {ID: "sess-foreign", TaskID: "other-task", State: taskmodels.TaskSessionStateRunning},
+		},
+	}
+	d := New(eng, sessions, logger.Default())
+
+	_, err := d.RecordDecision(context.Background(), RecordDecisionInput{
+		TaskID: "task-1", StepID: "review", ParticipantID: "participant-1",
+		Decision: "approved", SessionID: "sess-foreign",
+	})
+	if err != nil {
+		t.Fatalf("RecordDecision: %v, want success (session_unresolvable, not an error)", err)
+	}
+	if !eng.decisionCalled {
+		t.Fatal("engine RecordParticipantDecision not invoked")
+	}
+	if eng.decisionSession != "" {
+		t.Errorf("session id = %q, want blank: foreign session must not be forwarded", eng.decisionSession)
+	}
+}
+
+// TestDispatcher_RecordDecision_TerminalSessionFallsBackToUnresolvable
+// covers the other session_unresolvable case: a supplied session that
+// belongs to the right task but is in a terminal (non-active) state.
+func TestDispatcher_RecordDecision_TerminalSessionFallsBackToUnresolvable(t *testing.T) {
+	eng := &fakeEngine{decisionResult: engine.RecordDecisionResult{DecisionID: "decision-1"}}
+	sessions := &fakeSessions{
+		byID: map[string]*taskmodels.TaskSession{
+			"sess-done": {ID: "sess-done", TaskID: "task-1", State: taskmodels.TaskSessionStateCompleted},
+		},
+	}
+	d := New(eng, sessions, logger.Default())
+
+	_, err := d.RecordDecision(context.Background(), RecordDecisionInput{
+		TaskID: "task-1", StepID: "review", ParticipantID: "participant-1",
+		Decision: "approved", SessionID: "sess-done",
+	})
+	if err != nil {
+		t.Fatalf("RecordDecision: %v, want success (session_unresolvable, not an error)", err)
+	}
+	if eng.decisionSession != "" {
+		t.Errorf("session id = %q, want blank: terminal session must not be forwarded", eng.decisionSession)
+	}
+}
+
+// TestDispatcher_RecordDecision_MissingSessionFallsBackToUnresolvable
+// covers the third session_unresolvable case: a supplied session id that
+// does not exist at all (e.g. a stale/deleted session).
+func TestDispatcher_RecordDecision_MissingSessionFallsBackToUnresolvable(t *testing.T) {
+	eng := &fakeEngine{decisionResult: engine.RecordDecisionResult{DecisionID: "decision-1"}}
+	sessions := &fakeSessions{} // byID is nil: GetTaskSession returns ErrTaskSessionNotFound
+	d := New(eng, sessions, logger.Default())
+
+	_, err := d.RecordDecision(context.Background(), RecordDecisionInput{
+		TaskID: "task-1", StepID: "review", ParticipantID: "participant-1",
+		Decision: "approved", SessionID: "sess-missing",
+	})
+	if err != nil {
+		t.Fatalf("RecordDecision: %v, want success (session_unresolvable, not an error)", err)
+	}
+	if eng.decisionSession != "" {
+		t.Errorf("session id = %q, want blank: missing session must not be forwarded", eng.decisionSession)
+	}
+}
+
+// TestDispatcher_RecordDecision_SessionLookupErrorPropagates proves a
+// genuine session-store failure while resolving the supplied SessionID is
+// not silently swallowed as session_unresolvable — mirroring
+// TestDispatcher_RecordDecision_PropagatesActiveSessionLookupError for the
+// resolveActiveSessionID path.
+func TestDispatcher_RecordDecision_SessionLookupErrorPropagates(t *testing.T) {
+	dbErr := errors.New("db down")
+	eng := &fakeEngine{}
+	sessions := &fakeSessions{byIDErr: dbErr}
+	d := New(eng, sessions, logger.Default())
+
+	_, err := d.RecordDecision(context.Background(), RecordDecisionInput{
+		TaskID: "task-1", StepID: "review", ParticipantID: "participant-1",
+		Decision: "approved", SessionID: "sess-1",
+	})
+	if !errors.Is(err, dbErr) {
+		t.Fatalf("err = %v, want wrapped db error", err)
+	}
+	if eng.decisionCalled {
+		t.Error("engine should not be called when session lookup fails")
+	}
+}
diff --git a/apps/backend/internal/orchestrator/handoff_inheritance_test.go b/apps/backend/internal/orchestrator/handoff_inheritance_test.go
index f13ccf8b3c..9322840747 100644
--- a/apps/backend/internal/orchestrator/handoff_inheritance_test.go
+++ b/apps/backend/internal/orchestrator/handoff_inheritance_test.go
@@ -97,7 +97,7 @@ func TestPrepareSessionForStart_PropagatesInheritedEnvironment(t *testing.T) {
 		ParentID: "parent",
 		Metadata: map[string]interface{}{"workspace": map[string]interface{}{"mode": "inherit_parent"}},
 	}
-	sessionID, _, err := svc.prepareSessionForStart(ctx, childTask, "profile-1", "exec-1", "", "")
+	sessionID, _, err := svc.prepareSessionForStart(ctx, childTask, "profile-1", "profile-1", "exec-1", "", "")
 	if err != nil {
 		t.Fatalf("prepareSessionForStart: %v", err)
 	}
@@ -125,7 +125,7 @@ func TestPrepareSessionForStart_InheritedWorkspaceMissingCompensatesSession(t *t
 		ID:       "child-missing",
 		ParentID: "parent-missing",
 		Metadata: map[string]interface{}{"workspace": map[string]interface{}{"mode": "inherit_parent"}},
-	}, "profile-1", "exec-1", "", "")
+	}, "profile-1", "profile-1", "exec-1", "", "")
 	if !errors.Is(err, models.ErrWorkspaceReuseUnsafe) {
 		t.Fatalf("prepareSessionForStart error = %v, want workspace reuse unsafe", err)
 	}
diff --git a/apps/backend/internal/orchestrator/service.go b/apps/backend/internal/orchestrator/service.go
index d3b05fdeda..efa712c0c0 100644
--- a/apps/backend/internal/orchestrator/service.go
+++ b/apps/backend/internal/orchestrator/service.go
@@ -63,6 +63,12 @@ type ServiceConfig struct {
 	// turn for an agent that advertised prompt queueing. Independent of
 	// ClaudeBackgroundPromptHandoff, which covers the foreground-idle handoff.
 	ClaudeMidTurnSteering bool
+
+	// OfficeSessionIdentity keys an Office task's session identity on the
+	// run's own agent instead of the task's runner seat. Off by default;
+	// enabling it exposes pre-existing duplicate (task_id, agent_profile_id)
+	// rows until the companion unique-index fix has shipped.
+	OfficeSessionIdentity bool
 }
 
 // AttachmentReader is the narrow attachment-store seam needed when the
diff --git a/apps/backend/internal/orchestrator/session_ensure.go b/apps/backend/internal/orchestrator/session_ensure.go
index df503b8a2b..ae6b9b79c3 100644
--- a/apps/backend/internal/orchestrator/session_ensure.go
+++ b/apps/backend/internal/orchestrator/session_ensure.go
@@ -151,7 +151,7 @@ func (s *Service) EnsureSession(ctx context.Context, taskID string, opts ...Ensu
 // singleton human user). For kanban tasks, it falls back to the existing
 // is_primary-first lookup. Returns nil when no matching session exists.
 func (s *Service) findExistingSession(ctx context.Context, taskID string) *EnsureSessionResponse {
-	if office := s.findOfficeSessionForResume(ctx, taskID); office != nil {
+	if office, isOffice := s.findOfficeSessionForResume(ctx, taskID); isOffice {
 		return office
 	}
 	sessions, err := s.repo.ListTaskSessions(ctx, taskID)
@@ -168,24 +168,36 @@ func (s *Service) findExistingSession(ctx context.Context, taskID string) *Ensur
 }
 
 // findOfficeSessionForResume implements the office-only branch of advanced-mode
-// resume. Returns nil when the task isn't office, when no per-agent session
-// has been created yet, or when no relevant agent identity is available.
-// (The "create on demand" branch is handled by EnsureSession's fallthrough,
-// not here — keeping findExistingSession a pure lookup.)
-func (s *Service) findOfficeSessionForResume(ctx context.Context, taskID string) *EnsureSessionResponse {
+// resume. The second return value reports whether the task is Office-owned.
+// Returns nil when no per-agent session has been created yet or when no
+// relevant agent identity is available. An Office task must not fall through to
+// the generic primary/newest lookup, because that lookup can return another
+// participant's session. When the task has no projected runner (for example,
+// a task created with only metadata.agent_profile_id), resolve the same profile
+// EnsureSession would use for creation and look up that exact session. The
+// "create on demand" branch is handled by EnsureSession after this pure lookup.
+func (s *Service) findOfficeSessionForResume(ctx context.Context, taskID string) (*EnsureSessionResponse, bool) {
 	task, err := s.repo.GetTask(ctx, taskID)
 	if err != nil || task == nil || !task.IsFromOffice {
-		return nil
+		return nil, false
 	}
 	agentID := s.agentForViewer(ctx, task)
 	if agentID == "" {
-		return nil
+		// A task can be Office-owned without a projected runner. This is
+		// common for API-created review tasks whose concrete profile lives in
+		// metadata. Match the profile resolution used by EnsureSession so an
+		// already-created run session is reused while still avoiding a
+		// participant-agnostic newest-session fallback.
+		agentID, _ = s.resolveTaskAgentProfile(ctx, task)
+	}
+	if agentID == "" {
+		return nil, true
 	}
 	sess, err := s.repo.GetTaskSessionByTaskAndAgent(ctx, taskID, agentID)
 	if err != nil || sess == nil {
-		return nil
+		return nil, true
 	}
-	return s.existingResponse(ctx, taskID, sess, "existing_office_agent")
+	return s.existingResponse(ctx, taskID, sess, "existing_office_agent"), true
 }
 
 // agentForViewer resolves the agent_profile_id whose session should be
diff --git a/apps/backend/internal/orchestrator/session_ensure_office_test.go b/apps/backend/internal/orchestrator/session_ensure_office_test.go
index 68bde00025..022ff7a490 100644
--- a/apps/backend/internal/orchestrator/session_ensure_office_test.go
+++ b/apps/backend/internal/orchestrator/session_ensure_office_test.go
@@ -79,6 +79,86 @@ func TestFindExistingSession_OfficeTaskWithViewerAgent(t *testing.T) {
 	}
 }
 
+func TestFindExistingSession_OfficeTaskWithOnlyOtherAgentSessionReturnsNil(t *testing.T) {
+	repo := setupTestRepo(t)
+	seedOfficeTaskAndSessions(t, repo)
+	if err := repo.DeleteTaskSession(context.Background(), "s-assignee"); err != nil {
+		t.Fatalf("delete assignee session: %v", err)
+	}
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+
+	if got := svc.findExistingSession(context.Background(), "t-office"); got != nil {
+		t.Fatalf("expected no assignee session, got %q", got.SessionID)
+	}
+}
+
+func TestFindExistingSession_OfficeTaskUsesResolvedMetadataProfile(t *testing.T) {
+	repo := setupTestRepo(t)
+	ctx := context.Background()
+	seedOfficeTaskAndSessions(t, repo)
+	if err := repo.DeleteTaskSession(ctx, "s-assignee"); err != nil {
+		t.Fatalf("delete assignee session: %v", err)
+	}
+	task, err := repo.GetTask(ctx, "t-office")
+	if err != nil {
+		t.Fatalf("get task: %v", err)
+	}
+	task.AssigneeAgentProfileID = ""
+	task.Metadata = map[string]interface{}{"agent_profile_id": "agent-reviewer"}
+	if err := repo.UpdateTask(ctx, task); err != nil {
+		t.Fatalf("update task: %v", err)
+	}
+
+	svc := createTestService(repo, newMockStepGetter(), newMockTaskRepo())
+	resp := svc.findExistingSession(ctx, "t-office")
+	if resp == nil {
+		t.Fatal("expected metadata-resolved session, got nil")
+	}
+	if resp.SessionID != "s-reviewer" {
+		t.Fatalf("session_id = %q, want s-reviewer", resp.SessionID)
+	}
+}
+
+func TestPrepareTaskSession_OfficeFlagUsesAssigneeForSessionIdentity(t *testing.T) {
+	ctx := context.Background()
+	repo := setupTestRepo(t)
+	seedOfficeTaskAndSessions(t, repo)
+	if err := repo.DeleteTaskSession(ctx, "s-assignee"); err != nil {
+		t.Fatalf("delete assignee session: %v", err)
+	}
+	if err := repo.DeleteTaskSession(ctx, "s-reviewer"); err != nil {
+		t.Fatalf("delete reviewer session: %v", err)
+	}
+
+	taskRepo := newMockTaskRepo()
+	taskRepo.tasks["t-office"] = &v1.Task{
+		ID:          "t-office",
+		WorkspaceID: "ws-r",
+		WorkflowID:  "wf-r",
+		Title:       "Office",
+		State:       v1.TaskStateInProgress,
+	}
+	svc := createTestServiceWithScheduler(repo, newMockStepGetter(), taskRepo, &mockAgentManager{})
+	svc.config.OfficeSessionIdentity = true
+
+	sessionID, err := svc.PrepareTaskSession(
+		ctx, "t-office", "execution-profile", "", "", "", false,
+	)
+	if err != nil {
+		t.Fatalf("PrepareTaskSession: %v", err)
+	}
+	session, err := repo.GetTaskSession(ctx, sessionID)
+	if err != nil {
+		t.Fatalf("get prepared session: %v", err)
+	}
+	if session.AgentProfileID != "agent-assignee" {
+		t.Fatalf("session identity = %q, want agent-assignee", session.AgentProfileID)
+	}
+	if session.ExecutionProfileID != "execution-profile" {
+		t.Fatalf("execution profile = %q, want execution-profile", session.ExecutionProfileID)
+	}
+}
+
 // TestFindExistingSession_KanbanTask_UsesPrimary keeps the kanban-side
 // is_primary lookup intact under the new gating.
 func TestFindExistingSession_KanbanTask_UsesPrimary(t *testing.T) {
diff --git a/apps/backend/internal/orchestrator/session_ensure_test.go b/apps/backend/internal/orchestrator/session_ensure_test.go
index 1c865733a7..5a4360c937 100644
--- a/apps/backend/internal/orchestrator/session_ensure_test.go
+++ b/apps/backend/internal/orchestrator/session_ensure_test.go
@@ -126,9 +126,12 @@ func TestFindOfficeSessionForResumeUsesCanonicalOfficeProjection(t *testing.T) {
 			if tt.viewer != "" {
 				ctx = WithViewerAgent(ctx, tt.viewer)
 			}
-			got := svc.findOfficeSessionForResume(ctx, "task1")
-			if (got != nil) != tt.wantOffice {
-				t.Fatalf("office session found = %v, want %v", got != nil, tt.wantOffice)
+			got, isOffice := svc.findOfficeSessionForResume(ctx, "task1")
+			if isOffice != tt.wantOffice {
+				t.Fatalf("is office task = %v, want %v", isOffice, tt.wantOffice)
+			}
+			if (got != nil) != (tt.wantOffice && tt.viewer != "") {
+				t.Fatalf("office session found = %v, want %v", got != nil, tt.wantOffice && tt.viewer != "")
 			}
 		})
 	}
diff --git a/apps/backend/internal/orchestrator/task_operations.go b/apps/backend/internal/orchestrator/task_operations.go
index 86f39f8c22..09e50f1ed2 100644
--- a/apps/backend/internal/orchestrator/task_operations.go
+++ b/apps/backend/internal/orchestrator/task_operations.go
@@ -322,7 +322,10 @@ func (s *Service) PrepareTaskSession(ctx context.Context, taskID string, agentPr
 	// EnsureSessionForAgent so runs + advanced-mode reuse one row.
 	// prepareSessionForStart also propagates any inherited workspace
 	// environment (inherit_parent / shared_group) onto the new session.
-	sessionID, sessionCreated, err := s.prepareSessionForStart(ctx, task, agentProfileID, executorID, executorProfileID, workflowStepID)
+	// A manual prepare call has no scheduler-owned Office run identity. Keep the
+	// participant slot empty so createStartSession uses the task assignee, while
+	// agentProfileID remains the concrete execution profile.
+	sessionID, sessionCreated, err := s.prepareSessionForStart(ctx, task, agentProfileID, "", executorID, executorProfileID, workflowStepID)
 	if err != nil {
 		s.logger.Error("failed to prepare session",
 			zap.String("task_id", taskID),
@@ -1051,7 +1054,7 @@ func (s *Service) startTask(ctx context.Context, taskID string, agentProfileID s
 	// Prepare session first so we have the sessionID for config context injection.
 	// For office tasks, replace the per-launch PrepareSession with the per-(task,
 	// agent) EnsureSessionForAgent so runs reuse one row across turns.
-	sessionID, sessionCreated, err := s.prepareSessionForStart(ctx, task, agentProfileID, executorID, executorProfileID, workflowStepID)
+	sessionID, sessionCreated, err := s.prepareSessionForStart(ctx, task, agentProfileID, officeAgentProfileID, executorID, executorProfileID, workflowStepID)
 	if err != nil {
 		return nil, err
 	}
@@ -1394,9 +1397,9 @@ func validateOfficeLaunchEnv(taskID string, env map[string]string) error {
 // propagateInheritedEnvironment is a no-op for tasks without a workspace policy.
 func (s *Service) prepareSessionForStart(
 	ctx context.Context, task *v1.Task,
-	agentProfileID, executorID, executorProfileID, workflowStepID string,
+	agentProfileID, officeAgentProfileID, executorID, executorProfileID, workflowStepID string,
 ) (string, bool, error) {
-	sessionID, created, err := s.createStartSession(ctx, task, agentProfileID, executorID, executorProfileID, workflowStepID)
+	sessionID, created, err := s.createStartSession(ctx, task, agentProfileID, officeAgentProfileID, executorID, executorProfileID, workflowStepID)
 	if err != nil {
 		return "", false, err
 	}
@@ -1585,25 +1588,60 @@ func (s *Service) recordDynamicRouteResolutionFailure(
 }
 
 // createStartSession picks the right session-creation path for the task:
-// Office tasks with an assignee use the per-(task, agent) EnsureSessionForAgent
-// (so runs reuse one row across turns); kanban / quick-chat fall through to
-// the per-launch PrepareSession used since day one.
+// Office tasks use the per-(task, agent) EnsureSessionForAgent path (so runs
+// reuse one row across turns); kanban / quick-chat fall through to the
+// per-launch PrepareSession used since day one. An Office task can be created
+// before its runner seat is projected, so the run's captured identity or its
+// resolved execution profile supplies the owner until the seat is assigned.
+//
+// The session-owner identity passed to EnsureSessionForAgentWithCreation is,
+// by default, the task's runner seat (dbTask.AssigneeAgentProfileID) — even
+// for a reviewer/approver run whose agent differs from the runner, which
+// wrongly binds that run's session (and later its decisions) to the runner's
+// identity. When features.officeSessionIdentity is on, officeAgentProfileID
+// (the run's own agent, captured by the caller before step/routing overrides
+// mutate agentProfileID) is used instead so each participant agent gets its
+// own session per task.
 func (s *Service) createStartSession(
 	ctx context.Context, task *v1.Task,
-	agentProfileID, executorID, executorProfileID, workflowStepID string,
+	agentProfileID, officeAgentProfileID, executorID, executorProfileID, workflowStepID string,
 ) (string, bool, error) {
 	dbTask, err := s.repo.GetTask(ctx, task.ID)
-	if err == nil && dbTask != nil && dbTask.IsFromOffice && dbTask.AssigneeAgentProfileID != "" {
-		session, created, ensureErr := s.executor.EnsureSessionForAgentWithCreation(
-			ctx, task, dbTask.AssigneeAgentProfileID, agentProfileID, executorID, executorProfileID,
-		)
-		if ensureErr != nil {
-			return "", false, ensureErr
-		}
-		return session.ID, created, nil
+	if err != nil || dbTask == nil || !dbTask.IsFromOffice {
+		sessionID, prepareErr := s.executor.PrepareSession(ctx, task, agentProfileID, executorID, executorProfileID, workflowStepID)
+		return sessionID, prepareErr == nil, prepareErr
 	}
-	sessionID, err := s.executor.PrepareSession(ctx, task, agentProfileID, executorID, executorProfileID, workflowStepID)
-	return sessionID, err == nil, err
+
+	sessionOwnerID := s.officeSessionOwnerID(dbTask, agentProfileID, officeAgentProfileID)
+	if sessionOwnerID == "" {
+		sessionID, prepareErr := s.executor.PrepareSession(ctx, task, agentProfileID, executorID, executorProfileID, workflowStepID)
+		return sessionID, prepareErr == nil, prepareErr
+	}
+	session, created, ensureErr := s.executor.EnsureSessionForAgentWithCreation(
+		ctx, task, sessionOwnerID, agentProfileID, executorID, executorProfileID,
+	)
+	if ensureErr != nil {
+		return "", false, ensureErr
+	}
+	return session.ID, created, nil
+}
+
+// officeSessionOwnerID selects the stable identity for an Office session. A
+// projected runner wins by default. When identity separation is enabled, a
+// scheduler-captured participant identity wins for assigned runs. Before a
+// runner seat is projected, the captured identity or execution profile keeps
+// the session on the Office path instead of creating a generic workspace row.
+func (s *Service) officeSessionOwnerID(task *models.Task, agentProfileID, officeAgentProfileID string) string {
+	if task.AssigneeAgentProfileID == "" {
+		if officeAgentProfileID != "" {
+			return officeAgentProfileID
+		}
+		return agentProfileID
+	}
+	if s.config.OfficeSessionIdentity && officeAgentProfileID != "" {
+		return officeAgentProfileID
+	}
+	return task.AssigneeAgentProfileID
 }
 
 // moveTaskToWorkflowStep moves a task to the target workflow step if provided and different from current.
diff --git a/apps/backend/internal/orchestrator/task_operations_test.go b/apps/backend/internal/orchestrator/task_operations_test.go
index ae4ba623c1..1f742f75b8 100644
--- a/apps/backend/internal/orchestrator/task_operations_test.go
+++ b/apps/backend/internal/orchestrator/task_operations_test.go
@@ -173,7 +173,7 @@ func TestCreateStartSession_KanbanRunnerCreatesDistinctSession(t *testing.T) {
 	if isOffice {
 		t.Fatal("kanban task with a runner was classified as office-owned")
 	}
-	sessionID, _, err := svc.createStartSession(ctx, task.ToAPI(), "copilot-runner", "", "", "")
+	sessionID, _, err := svc.createStartSession(ctx, task.ToAPI(), "copilot-runner", "copilot-runner", "", "", "")
 	if err != nil {
 		t.Fatalf("create start session: %v", err)
 	}
@@ -226,7 +226,7 @@ func TestCreateStartSession_OfficeRunnerReusesPersistentSession(t *testing.T) {
 	if !isOffice {
 		t.Fatal("office-owned assigned task was not classified as office")
 	}
-	sessionID, created, err := svc.createStartSession(ctx, task.ToAPI(), "copilot-runner", "", "", "")
+	sessionID, created, err := svc.createStartSession(ctx, task.ToAPI(), "copilot-runner", "copilot-runner", "", "", "")
 	if err != nil {
 		t.Fatalf("create start session: %v", err)
 	}
@@ -238,6 +238,177 @@ func TestCreateStartSession_OfficeRunnerReusesPersistentSession(t *testing.T) {
 	}
 }
 
+func TestCreateStartSession_OfficeUnassignedReusesResolvedProfileSession(t *testing.T) {
+	ctx := context.Background()
+	repo := setupTestRepo(t)
+	now := time.Now().UTC()
+
+	if err := repo.CreateWorkspace(ctx, &models.Workspace{ID: "ws-office-unassigned", Name: "Office", CreatedAt: now, UpdatedAt: now}); err != nil {
+		t.Fatalf("create workspace: %v", err)
+	}
+	if err := repo.CreateWorkflow(ctx, &models.Workflow{ID: "wf-office-unassigned", WorkspaceID: "ws-office-unassigned", Name: "Office", CreatedAt: now, UpdatedAt: now}); err != nil {
+		t.Fatalf("create workflow: %v", err)
+	}
+	if err := seedWorkflowStep(t, repo, "step-office-unassigned"); err != nil {
+		t.Fatalf("create workflow step: %v", err)
+	}
+	if err := repo.CreateTask(ctx, &models.Task{
+		ID: "task-office-unassigned", WorkspaceID: "ws-office-unassigned", WorkflowID: "wf-office-unassigned", WorkflowStepID: "step-office-unassigned",
+		Title: "Office task", State: v1.TaskStateInProgress, ProjectID: "office-project",
+		Metadata:  map[string]interface{}{models.MetaKeyAgentProfileID: "ceo-reviewer"},
+		CreatedAt: now, UpdatedAt: now,
+	}); err != nil {
+		t.Fatalf("create task: %v", err)
+	}
+
+	task, err := repo.GetTask(ctx, "task-office-unassigned")
+	if err != nil {
+		t.Fatalf("get task: %v", err)
+	}
+	if !task.IsFromOffice {
+		t.Fatal("office task was not projected as office-owned")
+	}
+	if task.AssigneeAgentProfileID != "" {
+		t.Fatalf("task unexpectedly has an assignee: %q", task.AssigneeAgentProfileID)
+	}
+
+	svc := createTestServiceWithScheduler(repo, newMockStepGetter(), newMockTaskRepo(), &mockAgentManager{})
+	firstID, firstCreated, err := svc.createStartSession(ctx, task.ToAPI(), "ceo-reviewer", "", "", "", "")
+	if err != nil {
+		t.Fatalf("first create start session: %v", err)
+	}
+	if !firstCreated {
+		t.Fatal("first office launch should create a session")
+	}
+
+	secondID, secondCreated, err := svc.createStartSession(ctx, task.ToAPI(), "ceo-reviewer", "", "", "", "")
+	if err != nil {
+		t.Fatalf("second create start session: %v", err)
+	}
+	if secondCreated {
+		t.Fatal("second office launch should reuse the profile session")
+	}
+	if secondID != firstID {
+		t.Fatalf("reused session = %q, want first session %q", secondID, firstID)
+	}
+}
+
+// TestCreateStartSession_ReviewerRunFlagOff is the regression baseline: a
+// review run whose agent (ceo-reviewer) differs from the task's runner seat
+// (pm-runner) lands in the runner's session when features.officeSessionIdentity
+// is off (the default), reproducing the FORBIDDEN bug this task fixes —
+// record_step_decision_kandev resolves the session's AgentProfileID as the
+// decider identity, so the reviewer's own decision is checked against seats
+// the runner (not the reviewer) occupies.
+func TestCreateStartSession_ReviewerRunFlagOff(t *testing.T) {
+	ctx := context.Background()
+	repo := setupTestRepo(t)
+	now := time.Now().UTC()
+
+	if err := repo.CreateWorkspace(ctx, &models.Workspace{ID: "ws-review", Name: "Review", CreatedAt: now, UpdatedAt: now}); err != nil {
+		t.Fatalf("create workspace: %v", err)
+	}
+	if err := repo.CreateWorkflow(ctx, &models.Workflow{ID: "wf-review", WorkspaceID: "ws-review", Name: "Review", CreatedAt: now, UpdatedAt: now}); err != nil {
+		t.Fatalf("create workflow: %v", err)
+	}
+	if err := seedWorkflowStep(t, repo, "step-review-start"); err != nil {
+		t.Fatalf("create workflow step: %v", err)
+	}
+	if err := repo.CreateTask(ctx, &models.Task{
+		ID: "task-review", WorkspaceID: "ws-review", WorkflowID: "wf-review", WorkflowStepID: "step-review-start",
+		Title: "Review task", State: v1.TaskStateInProgress, ProjectID: "office-project", AssigneeAgentProfileID: "pm-runner",
+		CreatedAt: now, UpdatedAt: now,
+	}); err != nil {
+		t.Fatalf("create task: %v", err)
+	}
+	if err := repo.CreateTaskSession(ctx, &models.TaskSession{
+		ID: "runner-session", TaskID: "task-review", AgentProfileID: "pm-runner",
+		State: models.TaskSessionStateRunning, StartedAt: now, UpdatedAt: now,
+	}); err != nil {
+		t.Fatalf("create runner session: %v", err)
+	}
+
+	task, err := repo.GetTask(ctx, "task-review")
+	if err != nil {
+		t.Fatalf("get task: %v", err)
+	}
+
+	svc := createTestServiceWithScheduler(repo, newMockStepGetter(), newMockTaskRepo(), &mockAgentManager{})
+
+	// A reviewer run: the run's own agent (ceo-reviewer) differs from the
+	// task's runner seat (pm-runner).
+	sessionID, _, err := svc.createStartSession(ctx, task.ToAPI(), "ceo-reviewer", "ceo-reviewer", "", "", "")
+	if err != nil {
+		t.Fatalf("create start session: %v", err)
+	}
+	session, err := repo.GetTaskSession(ctx, sessionID)
+	if err != nil {
+		t.Fatalf("get session: %v", err)
+	}
+	if session.AgentProfileID != "pm-runner" {
+		t.Fatalf("session owner = %q, want pm-runner (flag off preserves runner-keyed identity)", session.AgentProfileID)
+	}
+}
+
+// TestCreateStartSession_ReviewerRunFlagOnGetsOwnSession is the fix's green
+// case: with features.officeSessionIdentity on, the same reviewer run lands
+// in a session keyed on the run's own agent (ceo-reviewer), not the task's
+// runner seat (pm-runner).
+func TestCreateStartSession_ReviewerRunFlagOnGetsOwnSession(t *testing.T) {
+	ctx := context.Background()
+	repo := setupTestRepo(t)
+	now := time.Now().UTC()
+
+	if err := repo.CreateWorkspace(ctx, &models.Workspace{ID: "ws-review2", Name: "Review2", CreatedAt: now, UpdatedAt: now}); err != nil {
+		t.Fatalf("create workspace: %v", err)
+	}
+	if err := repo.CreateWorkflow(ctx, &models.Workflow{ID: "wf-review2", WorkspaceID: "ws-review2", Name: "Review2", CreatedAt: now, UpdatedAt: now}); err != nil {
+		t.Fatalf("create workflow: %v", err)
+	}
+	if err := seedWorkflowStep(t, repo, "step-review2-start"); err != nil {
+		t.Fatalf("create workflow step: %v", err)
+	}
+	if err := repo.CreateTask(ctx, &models.Task{
+		ID: "task-review2", WorkspaceID: "ws-review2", WorkflowID: "wf-review2", WorkflowStepID: "step-review2-start",
+		Title: "Review task", State: v1.TaskStateInProgress, ProjectID: "office-project", AssigneeAgentProfileID: "pm-runner",
+		CreatedAt: now, UpdatedAt: now,
+	}); err != nil {
+		t.Fatalf("create task: %v", err)
+	}
+	if err := repo.CreateTaskSession(ctx, &models.TaskSession{
+		ID: "runner-session2", TaskID: "task-review2", AgentProfileID: "pm-runner",
+		State: models.TaskSessionStateRunning, StartedAt: now, UpdatedAt: now,
+	}); err != nil {
+		t.Fatalf("create runner session: %v", err)
+	}
+
+	task, err := repo.GetTask(ctx, "task-review2")
+	if err != nil {
+		t.Fatalf("get task: %v", err)
+	}
+
+	svc := createTestServiceWithScheduler(repo, newMockStepGetter(), newMockTaskRepo(), &mockAgentManager{})
+	svc.config.OfficeSessionIdentity = true
+
+	sessionID, created, err := svc.createStartSession(ctx, task.ToAPI(), "ceo-reviewer", "ceo-reviewer", "", "", "")
+	if err != nil {
+		t.Fatalf("create start session: %v", err)
+	}
+	if !created {
+		t.Fatal("reviewer run should create its own session, not reuse the runner's")
+	}
+	if sessionID == "runner-session2" {
+		t.Fatal("reviewer run landed in the runner's session instead of its own")
+	}
+	session, err := repo.GetTaskSession(ctx, sessionID)
+	if err != nil {
+		t.Fatalf("get session: %v", err)
+	}
+	if session.AgentProfileID != "ceo-reviewer" {
+		t.Fatalf("session owner = %q, want ceo-reviewer", session.AgentProfileID)
+	}
+}
+
 func newCoordinatorStopTestService(
 	repo repoStore,
 	taskRepo scheduler.TaskRepository,
diff --git a/apps/backend/internal/profiles/profiles.yaml b/apps/backend/internal/profiles/profiles.yaml
index e97e4fddf9..d5e1ddadba 100644
--- a/apps/backend/internal/profiles/profiles.yaml
+++ b/apps/backend/internal/profiles/profiles.yaml
@@ -76,6 +76,15 @@ features:
     dev:  "false"
     e2e:  "false"
 
+  # High-risk Office per-agent session identity experiment: keys an Office
+  # task's session on the run's own agent instead of the runner seat. Off in
+  # every profile until the companion (task_id, agent_profile_id) unique-index
+  # fix has shipped, since pre-existing duplicate rows would otherwise be exposed.
+  KANDEV_FEATURES_OFFICE_SESSION_IDENTITY:
+    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/runtimeflags/registry.go b/apps/backend/internal/runtimeflags/registry.go
index 8449de478f..267f6f4d62 100644
--- a/apps/backend/internal/runtimeflags/registry.go
+++ b/apps/backend/internal/runtimeflags/registry.go
@@ -120,6 +120,23 @@ var registrations = []runtimeFlagRegistration{
 		read:  func(cfg *config.Config) bool { return cfg.Features.ClaudeMidTurnSteering },
 		apply: func(cfg *config.Config, value bool) { cfg.Features.ClaudeMidTurnSteering = value },
 	},
+	{
+		definition: RuntimeFlagDefinition{
+			Key:         "features.officeSessionIdentity",
+			EnvVar:      "KANDEV_FEATURES_OFFICE_SESSION_IDENTITY",
+			Kind:        KindFeature,
+			Label:       "Office per-agent session identity",
+			Description: "Keys an Office task's session identity on the run's own agent instead of the task's runner seat, and binds an agent's decision re-evaluation to its own calling session.",
+			Stability:   StabilityExperimental,
+			RiskLevel:   RiskHigh,
+			RiskDescription: "Changes durable Office session identity: each participant agent gets its own session per task instead of sharing the runner's, and existing session rows are not migrated. " +
+				"Enable only after the companion (task_id, agent_profile_id) unique-index fix has shipped, since pre-existing duplicate rows are otherwise exposed.",
+			RestartRequired: true,
+			Mutable:         true,
+		},
+		read:  func(cfg *config.Config) bool { return cfg.Features.OfficeSessionIdentity },
+		apply: func(cfg *config.Config, value bool) { cfg.Features.OfficeSessionIdentity = value },
+	},
 	{
 		definition: RuntimeFlagDefinition{
 			Key:         "debug.devMode",
diff --git a/apps/web/lib/state/slices/features/types.ts b/apps/web/lib/state/slices/features/types.ts
index 9452d0c277..597abd67e9 100644
--- a/apps/web/lib/state/slices/features/types.ts
+++ b/apps/web/lib/state/slices/features/types.ts
@@ -12,6 +12,7 @@ export const defaultFeatureFlags = {
   dynamicAgentRouting: false,
   claudeBackgroundPromptHandoff: false,
   claudeMidTurnSteering: false,
+  officeSessionIdentity: false,
 } as const;
 
 export type FeatureName = keyof typeof defaultFeatureFlags;
diff --git a/docs/public/configuration.md b/docs/public/configuration.md
index b3cc4a5511..0e375f0905 100644
--- a/docs/public/configuration.md
+++ b/docs/public/configuration.md
@@ -473,6 +473,7 @@ Copying this entire file is unnecessary and can freeze old defaults in a deploym
 | Key | Environment lock | Production default | Effect |
 |---|---|---|---|
 | `features.dynamicAgentRouting` | `KANDEV_FEATURES_DYNAMIC_AGENT_ROUTING` | off | Experimental dynamic profiles with ordered provider-error fallback. |
+| `features.officeSessionIdentity` | `KANDEV_FEATURES_OFFICE_SESSION_IDENTITY` | off | Experimental Office participant sessions. Enable only after the `(task_id, agent_profile_id)` unique index is available. |
 | `debug.devMode` | `KANDEV_DEBUG_DEV_MODE` | off | High-risk diagnostic endpoints and ACP frame logging. |
 
 The `KANDEV_FEATURES_*` values have no canonical YAML keys. They are selected
diff --git a/docs/public/operations.md b/docs/public/operations.md
index f0f407f43b..18b723081a 100644
--- a/docs/public/operations.md
+++ b/docs/public/operations.md
@@ -499,6 +499,7 @@ Kandev warns when its live WebSocket connection has not recovered for three seco
 **Settings > System > Feature Toggles** currently exposes:
 
 - **Office mode**: experimental, medium risk, and off in the production profile by default.
+- **Office session identity**: experimental, high risk, and off in every profile by default. Enable it only after the `(task_id, agent_profile_id)` unique index is available. It gives each Office participant a separate task conversation and requires a restart.
 - **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. Urgent WebSocket connectivity warnings still remain visible while the feature is off.
 - **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.
 - **Unread divider**: a per-user setting at **Settings > General > Task Actions**. It defaults off, takes effect immediately, and controls both the Slack-style **New** divider and read-cursor updates while that user's transcript view is visible.