Let a queued message be taken back into the composer

internal/agents/queue.go

@@ -75,7 +75,42 @@ func (m *Manager) Message(ctx context.Context, sessionID, actor, text, model str
 	return sess, nil
 }
 
+func (m *Manager) Withdraw(ctx context.Context, taskID string, inputID int64, actor string) error {
+	task, err := m.store.GetTask(ctx, taskID)
+	if err != nil {
+		return err
+	}
+	sessions, err := m.store.ListSessions(ctx, taskID)
+	if err != nil {
+		return err
+	}
+	if len(sessions) == 0 {
+		return fmt.Errorf("%w: message %d is not queued", ErrConflict, inputID)
+	}
+	sess := sessions[len(sessions)-1]
+
+	unlock := m.lockDelivery(queueLockKey(taskID))
+	defer unlock()
+
+	err = m.store.WithdrawTaskInput(ctx, taskID, inputID, task.ProjectId, sess.Id, actor)
+	if errors.Is(err, store.ErrNotFound) {
+		return fmt.Errorf("%w: message %d is not queued", ErrConflict, inputID)
+	}
+	if err != nil {
+		return err
+	}
+	slog.Info("queued message withdrawn", "session", sess.Id, "task", taskID, "input", inputID, "actor", actor)
+	return nil
+}
+
+func queueLockKey(taskID string) string {
+	return "task:" + taskID
+}
+
 func (m *Manager) deliverQueued(ctx context.Context, sess api.AgentSession) (bool, error) {
+	unlock := m.lockDelivery(queueLockKey(sess.TaskId))
+	defer unlock()
+
 	inputs, err := m.store.TaskInputs(ctx, sess.TaskId)
 	if err != nil || len(inputs) == 0 {
 		return false, err
@@ -131,6 +166,9 @@ func (m *Manager) takeQueuedMidTurn(ctx context.Context, l *live) []store.TaskIn
 		return nil
 	}
 
+	unlock := m.lockDelivery(queueLockKey(l.taskID))
+	defer unlock()
+
 	inputs, err := m.store.TaskInputs(ctx, l.taskID)
 	if err != nil {
 		slog.Error("list queued messages", "session", l.id, "err", err)