Add ready_for_merge tool and prompt agents for it after review

internal/store/migrations/059-add-task-ready-prompt.sql

@@ -0,0 +1 @@
+ALTER TABLE tasks ADD COLUMN ready_prompt_n INTEGER NOT NULL DEFAULT 0;

internal/store/store.go

@@ -746,6 +746,34 @@ func (s *Store) SetTaskSummary(ctx context.Context, id, summary, actor string) e
 	})
 }
 
+func (s *Store) ReadyPromptN(ctx context.Context, id string) (int, error) {
+	n := 0
+	err := s.db.QueryRowContext(ctx, `SELECT ready_prompt_n FROM tasks WHERE id = ?`, id).Scan(&n)
+	if errors.Is(err, sql.ErrNoRows) {
+		return 0, ErrNotFound
+	}
+	return n, err
+}
+
+func (s *Store) SetReadyPromptN(ctx context.Context, id string, snapshotN int) error {
+	_, err := s.db.ExecContext(ctx, `UPDATE tasks SET ready_prompt_n = ? WHERE id = ?`, snapshotN, id)
+	return err
+}
+
+func (s *Store) MarkReady(ctx context.Context, id, overview, actor string) error {
+	return s.write(ctx, func(tx *sql.Tx, emit emitFunc) error {
+		projectID := ""
+		err := tx.QueryRowContext(ctx, `SELECT project_id FROM tasks WHERE id = ? AND status = ?`, id, string(api.TaskStatusActive)).Scan(&projectID)
+		if errors.Is(err, sql.ErrNoRows) {
+			return ErrNotFound
+		}
+		if err != nil {
+			return err
+		}
+		return emit(api.Event{Kind: "task.ready", ProjectId: &projectID, TaskId: &id, Actor: actor, Payload: map[string]any{"id": id, "overview": overview}})
+	})
+}
+
 func (s *Store) TaskSummary(ctx context.Context, id string) (string, error) {
 	summary := ""
 	err := s.db.QueryRowContext(ctx, `SELECT summary FROM tasks WHERE id = ?`, id).Scan(&summary)