Finalize safe session rollover without nested lock deadlock

Hop-State: A_06FN5XPBA1JMJNPS2MAR0D0 Hop-Proposal: R_06FN5XN2CX7XBZ4KF1JZZ2G Hop-Task: T_06FN3MBF98GWD4NA5PA1RWG Hop-Attempt: AT_06FN5TMC0J7DXV2JGF15T20
2026-07-11 13:55:33 -07:00
parent e887c8476d
commit 2f00b2dd3f
7 changed files with 499 additions and 14 deletions
@@ -415,6 +415,41 @@ func (s *Store) SetAgentSessionHead(ctx context.Context, agent, sessionID, state
 	return nil
 }

+// RetargetAgentSessions moves interactive sessions that currently point into
+// one attempt to a successor prompt. Reconciliation uses this so a follow-up
+// received while conflicts are being resolved reaches the reconciliation
+// workspace instead of reopening the stale source workspace.
+func (s *Store) RetargetAgentSessions(ctx context.Context, agent, fromAttemptID, expectedHeadID, toStateID string) error {
+	if strings.TrimSpace(agent) == "" || strings.TrimSpace(fromAttemptID) == "" ||
+		strings.TrimSpace(expectedHeadID) == "" || strings.TrimSpace(toStateID) == "" {
+		return errors.New("hop: agent, source attempt, expected head, and target state are required")
+	}
+	tx, err := s.db.BeginTx(ctx, nil)
+	if err != nil {
+		return fmt.Errorf("begin agent session retarget: %w", err)
+	}
+	defer tx.Rollback()
+	attempt, err := attemptTx(ctx, tx, fromAttemptID)
+	if err != nil {
+		return err
+	}
+	if attempt.HeadStateID != expectedHeadID {
+		return &HeadChangedError{Scope: "attempt", Expected: expectedHeadID, Actual: attempt.HeadStateID}
+	}
+	if _, err := tx.ExecContext(ctx,
+		`UPDATE agent_sessions
+		 SET head_state_id = ?, updated_at = ?
+		 WHERE agent = ?
+		   AND head_state_id IN (SELECT id FROM states WHERE attempt_id = ?)`,
+		toStateID, formatTime(time.Now().UTC()), agent, fromAttemptID); err != nil {
+		return fmt.Errorf("retarget agent sessions: %w", err)
+	}
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("commit agent session retarget: %w", err)
+	}
+	return nil
+}
+
 // CreateTaskAttemptPrompt atomically creates all three records. The prompt is
 // durable and the attempt head points to it before the transaction becomes
 // visible, so an orchestrator may safely deliver the prompt after this returns.
@@ -567,6 +602,8 @@ func (s *Store) CreateAttemptPrompt(
 	attempt Attempt,
 	prompt State,
 	parents []Parent,
+	sessionSourceAttemptID string,
+	expectedSourceHeadID string,
 ) (Attempt, State, error) {
 	now := time.Now().UTC()
 	if attempt.ID == "" {
@@ -625,6 +662,20 @@ func (s *Store) CreateAttemptPrompt(
 	if err := tx.QueryRowContext(ctx, `SELECT 1 FROM tasks WHERE id = ?`, attempt.TaskID).Scan(&taskExists); err != nil {
 		return Attempt{}, State{}, dbNotFound("task", attempt.TaskID, err)
 	}
+	if sessionSourceAttemptID != "" {
+		if expectedSourceHeadID == "" {
+			return Attempt{}, State{}, errors.New("hop: reconciliation source head is required")
+		}
+		sourceAttempt, err := attemptTx(ctx, tx, sessionSourceAttemptID)
+		if err != nil {
+			return Attempt{}, State{}, err
+		}
+		if sourceAttempt.HeadStateID != expectedSourceHeadID {
+			return Attempt{}, State{}, &HeadChangedError{
+				Scope: "attempt", Expected: expectedSourceHeadID, Actual: sourceAttempt.HeadStateID,
+			}
+		}
+	}
 	base, err := stateTx(ctx, tx, attempt.BaseStateID)
 	if err != nil {
 		return Attempt{}, State{}, fmt.Errorf("read reconciliation base state: %w", err)
@@ -659,6 +710,16 @@ func (s *Store) CreateAttemptPrompt(
 		`UPDATE attempts SET head_state_id = ? WHERE id = ?`, prompt.ID, attempt.ID); err != nil {
 		return Attempt{}, State{}, fmt.Errorf("install reconciliation attempt head: %w", err)
 	}
+	if sessionSourceAttemptID != "" {
+		if _, err := tx.ExecContext(ctx,
+			`UPDATE agent_sessions
+			 SET head_state_id = ?, updated_at = ?
+			 WHERE agent = ?
+			   AND head_state_id IN (SELECT id FROM states WHERE attempt_id = ?)`,
+			prompt.ID, formatTime(now), attempt.Agent, sessionSourceAttemptID); err != nil {
+			return Attempt{}, State{}, fmt.Errorf("retarget reconciliation sessions: %w", err)
+		}
+	}
 	if _, err := tx.ExecContext(ctx,
 		`UPDATE tasks SET status = 'reconciling' WHERE id = ?`, attempt.TaskID); err != nil {
 		return Attempt{}, State{}, fmt.Errorf("mark task reconciling: %w", err)
@@ -839,6 +900,17 @@ func (s *Store) CASAccept(
 		if err != nil {
 			return State{}, fmt.Errorf("read proposal parent: %w", err)
 		}
+		if proposal.AttemptID != "" {
+			attempt, err := attemptTx(ctx, tx, proposal.AttemptID)
+			if err != nil {
+				return State{}, err
+			}
+			if attempt.HeadStateID != proposal.ID {
+				return State{}, &HeadChangedError{
+					Scope: "attempt", Expected: proposal.ID, Actual: attempt.HeadStateID,
+				}
+			}
+		}
 		if accepted.TaskID == "" {
 			accepted.TaskID = proposal.TaskID
 		}
@@ -886,6 +958,17 @@ func (s *Store) CASAccept(
 		}
 	}
 	if accepted.TaskID != "" {
+		if accepted.AttemptID != "" {
+			if _, err := tx.ExecContext(ctx,
+				`UPDATE attempts
+				 SET status = 'completed'
+				 WHERE task_id = ?
+				   AND id != ?
+				   AND status NOT IN ('accepted', 'completed', 'failed', 'cancelled', 'rejected')`,
+				accepted.TaskID, accepted.AttemptID); err != nil {
+				return State{}, fmt.Errorf("complete superseded task attempts: %w", err)
+			}
+		}
 		if _, err := tx.ExecContext(ctx,
 			`UPDATE tasks SET status = 'accepted' WHERE id = ?`, accepted.TaskID); err != nil {
 			return State{}, fmt.Errorf("mark task accepted: %w", err)
@@ -949,6 +1032,33 @@ func (s *Store) AcceptedForProposal(ctx context.Context, proposalID string) (Sta
 	return state, true, nil
 }

+// AcceptedForTask returns the latest immutable accepted outcome produced by a
+// task. Unlike the mutable task status, this remains authoritative when an
+// older client has accidentally reactivated an already accepted task.
+func (s *Store) AcceptedForTask(ctx context.Context, taskID string) (State, bool, error) {
+	if strings.TrimSpace(taskID) == "" {
+		return State{}, false, errors.New("hop: task ID is required")
+	}
+	var id string
+	err := s.db.QueryRowContext(ctx,
+		`SELECT id
+		 FROM states
+		 WHERE task_id = ? AND kind = 'accepted'
+		 ORDER BY created_at DESC, id DESC
+		 LIMIT 1`, taskID).Scan(&id)
+	if errors.Is(err, sql.ErrNoRows) {
+		return State{}, false, nil
+	}
+	if err != nil {
+		return State{}, false, fmt.Errorf("find accepted state for task %s: %w", taskID, err)
+	}
+	state, err := s.GetState(ctx, id)
+	if err != nil {
+		return State{}, false, err
+	}
+	return state, true, nil
+}
+
 // ReconciliationPrompt returns the prompt already created to reconcile a
 // proposal against a particular accepted head. The pair is unique by
 // convention and makes `hop refresh` safe to retry.
@@ -1105,6 +1215,34 @@ func (s *Store) GetParents(ctx context.Context, stateID string) ([]Parent, error
 	return parents, nil
 }

+// StateDescendsFrom reports whether descendantID is the same state as, or has
+// any typed-parent path to, ancestorID. Session rollover uses state ancestry so
+// a mutable task status cannot hide unfinished prompts created after an older
+// accepted outcome.
+func (s *Store) StateDescendsFrom(ctx context.Context, descendantID, ancestorID string) (bool, error) {
+	if strings.TrimSpace(descendantID) == "" || strings.TrimSpace(ancestorID) == "" {
+		return false, errors.New("hop: descendant and ancestor state IDs are required")
+	}
+	var found int
+	err := s.db.QueryRowContext(ctx,
+		`WITH RECURSIVE ancestry(id) AS (
+			SELECT ?
+			UNION
+			SELECT parents.parent_state_id
+			FROM state_parents parents
+			JOIN ancestry ON parents.state_id = ancestry.id
+		 )
+		 SELECT 1 FROM ancestry WHERE id = ? LIMIT 1`,
+		descendantID, ancestorID).Scan(&found)
+	if errors.Is(err, sql.ErrNoRows) {
+		return false, nil
+	}
+	if err != nil {
+		return false, fmt.Errorf("inspect state ancestry: %w", err)
+	}
+	return found == 1, nil
+}
+
 func (s *Store) ParentByRole(ctx context.Context, stateID, role string) (Parent, error) {
 	var parent Parent
 	err := s.db.QueryRowContext(ctx,
@@ -194,6 +194,9 @@ func (s *Service) BeginPrompt(ctx context.Context, message, fromStateID, agent,
 	if redactedSession, findings := RedactPromptSecrets(sessionID); len(findings) > 0 || redactedSession != sessionID {
 		return PromptResult{}, errors.New("hop: refusing to use a potential credential as an agent session ID")
 	}
+	// Serialize interactive prompt capture with other begins. Acceptance checks
+	// the proposal's attempt head again inside its SQLite transaction, so a begin
+	// racing a land makes that proposal stale without sharing accept.lock.
 	release, err := acquireProjectLock(ctx, s.Root, "prompt")
 	if err != nil {
 		return PromptResult{}, err
@@ -204,7 +207,13 @@ func (s *Service) BeginPrompt(ctx context.Context, message, fromStateID, agent,
 		if stateID, exists, err := s.Store.AgentSessionHead(ctx, agent, sessionID); err != nil {
 			return PromptResult{}, err
 		} else if exists {
-			fromStateID = stateID
+			continuable, err := s.sessionStateContinuable(ctx, stateID)
+			if err != nil {
+				return PromptResult{}, err
+			}
+			if continuable {
+				fromStateID = stateID
+			}
 		}
 	}
 	result, err := s.CreatePrompt(ctx, message, fromStateID, agent)
@@ -219,6 +228,68 @@ func (s *Service) BeginPrompt(ctx context.Context, message, fromStateID, agent,
 	return result, nil
 }

+// sessionStateContinuable decides whether an implicit interactive-session
+// pointer still represents unfinished work. An immutable accepted state for
+// the task ends ordinary session continuation even if an older Hop build later
+// changed the task's mutable status back to active. A dirty post-proposal
+// workspace is preserved by continuing it instead of silently abandoning work.
+func (s *Service) sessionStateContinuable(ctx context.Context, stateID string) (bool, error) {
+	state, err := s.Store.GetState(ctx, stateID)
+	if err != nil {
+		return false, err
+	}
+	if state.TaskID == "" || state.AttemptID == "" {
+		return false, fmt.Errorf("session state %s does not belong to a task attempt", state.ID)
+	}
+	accepted, exists, err := s.Store.AcceptedForTask(ctx, state.TaskID)
+	if err != nil {
+		return false, err
+	}
+	if !exists {
+		return true, nil
+	}
+	attempt, err := s.Store.GetAttempt(ctx, state.AttemptID)
+	if err != nil {
+		return false, err
+	}
+	head, err := s.Store.GetState(ctx, attempt.HeadStateID)
+	if err != nil {
+		return false, err
+	}
+	covered, err := s.Store.StateDescendsFrom(ctx, accepted.ID, head.ID)
+	if err != nil {
+		return false, err
+	}
+	if !covered {
+		return true, nil
+	}
+	workspaceRepo, err := OpenRepository(attempt.Workspace)
+	if err != nil {
+		return false, err
+	}
+	workspaceTree, err := workspaceRepo.WorktreeTree(ctx, head.SourceTree)
+	if err != nil {
+		return false, err
+	}
+	if workspaceTree != head.SourceTree {
+		return true, nil
+	}
+
+	status := "completed"
+	if attempt.ID == accepted.AttemptID {
+		status = "accepted"
+	}
+	if attempt.Status != status {
+		if err := s.Store.UpdateAttemptStatus(ctx, attempt.ID, status); err != nil {
+			return false, err
+		}
+	}
+	if err := s.Store.UpdateTaskStatus(ctx, state.TaskID, "accepted"); err != nil {
+		return false, err
+	}
+	return false, nil
+}
+
 func (s *Service) createInitialPrompt(ctx context.Context, message, agent string) (PromptResult, error) {
 	accepted, err := s.Store.AcceptedHead(ctx)
 	if err != nil {
@@ -603,6 +674,11 @@ func (s *Service) accept(ctx context.Context, proposalID string, checkCommand []
 	if err != nil {
 		return AcceptResult{}, err
 	}
+	if attempt.HeadStateID != proposal.ID {
+		return AcceptResult{}, &HeadChangedError{
+			Scope: "attempt", Expected: proposal.ID, Actual: attempt.HeadStateID,
+		}
+	}
 	baseStateID := proposal.CanonicalAnchorID
 	if baseStateID == "" {
 		baseStateID = attempt.BaseStateID
@@ -804,6 +880,11 @@ func (s *Service) Refresh(ctx context.Context, proposalID string) (RefreshResult
 	if err != nil {
 		return RefreshResult{}, err
 	}
+	if sourceAttempt.HeadStateID != proposal.ID {
+		return RefreshResult{}, &HeadChangedError{
+			Scope: "attempt", Expected: proposal.ID, Actual: sourceAttempt.HeadStateID,
+		}
+	}
 	task, err := s.Store.GetTask(ctx, proposal.TaskID)
 	if err != nil {
 		return RefreshResult{}, err
@@ -815,6 +896,9 @@ func (s *Service) Refresh(ctx context.Context, proposalID string) (RefreshResult
 	if existing, exists, err := s.Store.ReconciliationPrompt(ctx, proposal.ID, current.ID); err != nil {
 		return RefreshResult{}, err
 	} else if exists {
+		if err := s.Store.RetargetAgentSessions(ctx, sourceAttempt.Agent, sourceAttempt.ID, proposal.ID, existing.ID); err != nil {
+			return RefreshResult{}, err
+		}
 		return s.reconciliationResult(ctx, existing, task, proposal, current, true)
 	}
 	baseStateID := proposal.CanonicalAnchorID
@@ -901,7 +985,9 @@ func (s *Service) Refresh(ctx context.Context, proposalID string) (RefreshResult
 			_ = s.Repo.RemoveWorktree(context.Background(), workspace, true)
 		}
 	}()
-	reconciliationAttempt, prompt, err = s.Store.CreateAttemptPrompt(ctx, reconciliationAttempt, prompt, parents)
+	reconciliationAttempt, prompt, err = s.Store.CreateAttemptPrompt(
+		ctx, reconciliationAttempt, prompt, parents, sourceAttempt.ID, proposal.ID,
+	)
 	if err != nil {
 		return RefreshResult{}, err
 	}
@@ -242,7 +242,7 @@ func TestOpenProjectWaitsForInitializationLock(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-	case <-time.After(5 * time.Second):
+	case <-time.After(10 * time.Second):
 		t.Fatal("OpenProject did not resume after initialization lock release")
 	}
 }
@@ -364,6 +364,255 @@ func TestCLIBeginAutoInitializesAndContinuesCodexSession(t *testing.T) {
 	})
 }

+func TestBeginRollsAcceptedReconciliationSessionToCurrentHead(t *testing.T) {
+	ctx := context.Background()
+	service, _ := newTestProject(t, map[string]string{"shared.txt": "color=base\n"})
+
+	session, err := service.BeginPrompt(ctx, "Use blue", "", "codex", "thread-rollover")
+	if err != nil {
+		t.Fatal(err)
+	}
+	concurrent, err := service.CreatePrompt(ctx, "Use red", "", "other")
+	if err != nil {
+		t.Fatal(err)
+	}
+	writeTestFile(t, filepath.Join(session.Workspace, "shared.txt"), "color=blue\n")
+	writeTestFile(t, filepath.Join(concurrent.Workspace, "shared.txt"), "color=red\n")
+
+	sessionProposal, err := service.Propose(ctx, session.Prompt.ID, "Blue")
+	if err != nil {
+		t.Fatal(err)
+	}
+	concurrentProposal, err := service.Propose(ctx, concurrent.Prompt.ID, "Red")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := service.Land(ctx, concurrentProposal.Proposal.ID, nil); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := service.Land(ctx, sessionProposal.Proposal.ID, nil); err == nil {
+		t.Fatal("stale session proposal unexpectedly landed without reconciliation")
+	} else {
+		var conflict *ConflictError
+		if !errors.As(err, &conflict) {
+			t.Fatalf("land error = %v, want ConflictError", err)
+		}
+	}
+
+	reconciliation, err := service.Refresh(ctx, sessionProposal.Proposal.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	reconciliationHead, exists, err := service.Store.AgentSessionHead(ctx, "codex", "thread-rollover")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !exists || reconciliationHead != reconciliation.Prompt.ID {
+		t.Fatalf("session head = %q, %v; want reconciliation prompt %s", reconciliationHead, exists, reconciliation.Prompt.ID)
+	}
+	writeTestFile(t, filepath.Join(reconciliation.Workspace, "shared.txt"), "color=red-blue\n")
+	if _, err := service.RunCheck(ctx, reconciliation.Prompt.ID, []string{
+		"sh", "-c", `test "$(cat shared.txt)" = "color=red-blue"`,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	resolvedProposal, err := service.Propose(ctx, reconciliation.Prompt.ID, "Resolve red and blue")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := service.Land(ctx, resolvedProposal.Proposal.ID, nil); err != nil {
+		t.Fatal(err)
+	}
+	sourceAttempt, err := service.Store.GetAttempt(ctx, session.Attempt.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sourceAttempt.Status != "completed" {
+		t.Fatalf("source attempt status = %q, want completed", sourceAttempt.Status)
+	}
+
+	// Rollover must use the latest global accepted state, not merely this task's
+	// accepted outcome.
+	later, err := service.CreatePrompt(ctx, "Add a later accepted change", "", "other")
+	if err != nil {
+		t.Fatal(err)
+	}
+	writeTestFile(t, filepath.Join(later.Workspace, "later.txt"), "later\n")
+	laterProposal, err := service.Propose(ctx, later.Prompt.ID, "Later accepted change")
+	if err != nil {
+		t.Fatal(err)
+	}
+	laterAccepted, err := service.Land(ctx, laterProposal.Proposal.ID, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	next, err := service.BeginPrompt(ctx, "Next request", "", "codex", "thread-rollover")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertFreshRollover := func(label string, result PromptResult) {
+		t.Helper()
+		if result.Checkpoint != nil {
+			t.Fatalf("%s continued accepted session with checkpoint %s", label, result.Checkpoint.ID)
+		}
+		if result.Attempt.ID == session.Attempt.ID || result.Attempt.ID == reconciliation.Attempt.ID {
+			t.Fatalf("%s reused completed attempt %s", label, result.Attempt.ID)
+		}
+		if result.Task.ID == session.Task.ID {
+			t.Fatalf("%s reopened accepted task %s", label, result.Task.ID)
+		}
+		if result.Attempt.BaseStateID != laterAccepted.State.ID {
+			t.Fatalf("%s base = %s, want %s", label, result.Attempt.BaseStateID, laterAccepted.State.ID)
+		}
+		if result.Prompt.CanonicalAnchorID != laterAccepted.State.ID ||
+			result.Prompt.SourceTree != laterAccepted.State.SourceTree ||
+			result.Prompt.GitCommit != laterAccepted.State.GitCommit {
+			t.Fatalf("%s prompt was not rooted at latest accepted head: %#v; accepted=%#v", label, result.Prompt, laterAccepted.State)
+		}
+		if contents, err := os.ReadFile(filepath.Join(result.Workspace, "shared.txt")); err != nil || string(contents) != "color=red-blue\n" {
+			t.Fatalf("%s shared workspace = %q, err=%v", label, string(contents), err)
+		}
+		if contents, err := os.ReadFile(filepath.Join(result.Workspace, "later.txt")); err != nil || string(contents) != "later\n" {
+			t.Fatalf("%s later workspace = %q, err=%v", label, string(contents), err)
+		}
+	}
+	assertFreshRollover("normal reconciliation session", next)
+	head, exists, err := service.Store.AgentSessionHead(ctx, "codex", "thread-rollover")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !exists || head != next.Prompt.ID {
+		t.Fatalf("session head = %q, %v; want %s", head, exists, next.Prompt.ID)
+	}
+
+	// Older Hop builds could reactivate both records after acceptance. The
+	// immutable accepted outcome, not these mutable statuses, must drive rollover.
+	if err := service.Store.UpdateAttemptStatus(ctx, session.Attempt.ID, "active"); err != nil {
+		t.Fatal(err)
+	}
+	if err := service.Store.UpdateTaskStatus(ctx, session.Task.ID, "active"); err != nil {
+		t.Fatal(err)
+	}
+	if err := service.Store.SetAgentSessionHead(ctx, "codex", "legacy-thread-rollover", session.Prompt.ID); err != nil {
+		t.Fatal(err)
+	}
+	legacyNext, err := service.BeginPrompt(ctx, "Legacy next request", "", "codex", "legacy-thread-rollover")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertFreshRollover("legacy session", legacyNext)
+	sourceAttempt, err = service.Store.GetAttempt(ctx, session.Attempt.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sourceAttempt.Status == "active" {
+		t.Fatalf("source attempt %s was left active", sourceAttempt.ID)
+	}
+	head, exists, err = service.Store.AgentSessionHead(ctx, "codex", "legacy-thread-rollover")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !exists || head != legacyNext.Prompt.ID {
+		t.Fatalf("legacy session head = %q, %v; want %s", head, exists, legacyNext.Prompt.ID)
+	}
+}
+
+func TestLandRejectsProposalSupersededByFollowup(t *testing.T) {
+	ctx := context.Background()
+	service, initial := newTestProject(t, map[string]string{"base.txt": "base\n"})
+	started, err := service.BeginPrompt(ctx, "Create a change", "", "codex", "thread-stale-proposal")
+	if err != nil {
+		t.Fatal(err)
+	}
+	writeTestFile(t, filepath.Join(started.Workspace, "change.txt"), "first\n")
+	proposal, err := service.Propose(ctx, started.Prompt.ID, "First change")
+	if err != nil {
+		t.Fatal(err)
+	}
+	followup, err := service.BeginPrompt(ctx, "Refine that change", "", "codex", "thread-stale-proposal")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if followup.Attempt.ID != started.Attempt.ID || followup.Checkpoint == nil {
+		t.Fatalf("follow-up did not advance the original attempt: %#v", followup)
+	}
+	if _, err := service.Land(ctx, proposal.Proposal.ID, nil); !errors.Is(err, ErrAttemptHeadChanged) {
+		t.Fatalf("superseded proposal land error = %v, want ErrAttemptHeadChanged", err)
+	}
+	parents := canonicalizeParents([]Parent{
+		{StateID: initial.ID, Role: "canonical_parent", Order: 0},
+		{StateID: proposal.Proposal.ID, Role: "proposal_parent", Order: 1},
+	})
+	accepted := State{
+		ID:                newID("a"),
+		Kind:              StateAccepted,
+		TaskID:            proposal.Proposal.TaskID,
+		AttemptID:         proposal.Proposal.AttemptID,
+		CanonicalAnchorID: initial.ID,
+		SourceTree:        proposal.Proposal.SourceTree,
+		GitCommit:         proposal.Proposal.GitCommit,
+		Summary:           proposal.Proposal.Summary,
+		Agent:             proposal.Proposal.Agent,
+		CreatedAt:         time.Now().UTC(),
+		Parents:           parents,
+	}
+	accepted.Digest, err = digestState(accepted, parents)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := service.Store.CASAccept(ctx, initial.ID, accepted, parents); !errors.Is(err, ErrAttemptHeadChanged) {
+		t.Fatalf("transactional stale proposal error = %v, want ErrAttemptHeadChanged", err)
+	}
+	head, err := service.Store.AcceptedHead(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if head.ID != initial.ID {
+		t.Fatalf("superseded proposal advanced accepted head to %s", head.ID)
+	}
+}
+
+func TestBeginKeepsUnfinishedStateCreatedAfterAcceptedOutcome(t *testing.T) {
+	ctx := context.Background()
+	service, _ := newTestProject(t, map[string]string{"base.txt": "base\n"})
+	started, err := service.BeginPrompt(ctx, "Land the first change", "", "codex", "thread-post-accept")
+	if err != nil {
+		t.Fatal(err)
+	}
+	writeTestFile(t, filepath.Join(started.Workspace, "landed.txt"), "landed\n")
+	proposal, err := service.Propose(ctx, started.Prompt.ID, "Landed change")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := service.Land(ctx, proposal.Proposal.ID, nil); err != nil {
+		t.Fatal(err)
+	}
+
+	// Although agents must not mutate a frozen proposal, preserve any such
+	// residual work rather than silently rolling it away.
+	writeTestFile(t, filepath.Join(started.Workspace, "pending.txt"), "pending\n")
+	continued, err := service.BeginPrompt(ctx, "Preserve the pending work", "", "codex", "thread-post-accept")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if continued.Attempt.ID != started.Attempt.ID || continued.Checkpoint == nil {
+		t.Fatalf("dirty accepted workspace was not preserved: %#v", continued)
+	}
+	assertTreeFiles(t, service, continued.Checkpoint.GitCommit, map[string]string{
+		"base.txt":    "base\n",
+		"landed.txt":  "landed\n",
+		"pending.txt": "pending\n",
+	})
+	again, err := service.BeginPrompt(ctx, "Continue that pending work", "", "codex", "thread-post-accept")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if again.Attempt.ID != started.Attempt.ID || again.Checkpoint == nil {
+		t.Fatalf("post-acceptance prompt lineage was abandoned: %#v", again)
+	}
+}
+
 func TestDoctorRejectsCommitTreeAndDigestMismatch(t *testing.T) {
 	ctx := context.Background()
 	service, initial := newTestProject(t, map[string]string{"base.txt": "base\n"})