worker を追加（yt-dlp によるダウンロード、段階別進捗、ffprobe 検査、実行中の取り消し）

internal/store/store.go

@@ -183,6 +183,13 @@ func (s *Store) UpdateProgress(ctx context.Context, id int64, p Progress) error
 	return transitionResult(tag.RowsAffected(), err)
 }
 
+// Heartbeat は進捗出力がない間も実行中ジョブの生存を記録する。
+func (s *Store) Heartbeat(ctx context.Context, id int64) error {
+	tag, err := s.pool.Exec(ctx, `UPDATE download_jobs SET heartbeat_at=now(), updated_at=now()
+		WHERE id=$1 AND status='running'`, id)
+	return transitionResult(tag.RowsAffected(), err)
+}
+
 func (s *Store) Complete(ctx context.Context, id int64, filePath string, fileSizeBytes int64) error {
 	tag, err := s.pool.Exec(ctx, `UPDATE download_jobs SET status='succeeded', phase=NULL,
 		file_path=$2, file_size_bytes=$3, heartbeat_at=NULL, finished_at=now(), updated_at=now()
@@ -222,6 +229,16 @@ func (s *Store) RequeueStale(ctx context.Context, cutoff time.Time) (int64, erro
 	return tag.RowsAffected(), err
 }
 
+// RequeueRunning は worker の正常終了時に担当中ジョブを待機中へ戻す。
+func (s *Store) RequeueRunning(ctx context.Context, id int64) error {
+	tag, err := s.pool.Exec(ctx, `UPDATE download_jobs SET status='queued', phase=NULL,
+		downloaded_bytes=NULL, total_bytes=NULL, total_is_estimate=false, speed_bps=NULL,
+		eta_seconds=NULL, fragment_index=NULL, fragment_count=NULL, format_id=NULL,
+		heartbeat_at=NULL, started_at=NULL, updated_at=now()
+		WHERE id=$1 AND status='running'`, id)
+	return transitionResult(tag.RowsAffected(), err)
+}
+
 func transitionResult(count int64, err error) error {
 	if err != nil {
 		return err

internal/store/store_test.go

@@ -405,6 +405,47 @@ func TestCancelAndStaleBoundary(t *testing.T) {
 	}
 }
 
+func TestHeartbeatAndGracefulRequeue(t *testing.T) {
+	s := New(testPool(t, true))
+	ctx := context.Background()
+	job, _, err := s.Enqueue(ctx, sampleEpisode("heartbeat"), "manual")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Heartbeat(ctx, job.ID); !errors.Is(err, ErrInvalidTransition) {
+		t.Fatalf("待機中の heartbeat: %v", err)
+	}
+	claimed, err := s.ClaimNext(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	old := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+	if _, err := s.pool.Exec(ctx, `UPDATE download_jobs SET heartbeat_at=$2 WHERE id=$1`, claimed.ID, old); err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Heartbeat(ctx, claimed.ID); err != nil {
+		t.Fatal(err)
+	}
+	heartbeated, err := s.GetJob(ctx, claimed.ID)
+	if err != nil || heartbeated.HeartbeatAt == nil || !heartbeated.HeartbeatAt.After(old) {
+		t.Fatalf("heartbeat: %+v %v", heartbeated, err)
+	}
+	bytes := int64(10)
+	if err := s.UpdateProgress(ctx, claimed.ID, Progress{Phase: "video", DownloadedBytes: &bytes}); err != nil {
+		t.Fatal(err)
+	}
+	if err := s.RequeueRunning(ctx, claimed.ID); err != nil {
+		t.Fatal(err)
+	}
+	requeued, err := s.GetJob(ctx, claimed.ID)
+	if err != nil || requeued.Status != "queued" || requeued.StartedAt != nil || requeued.HeartbeatAt != nil || requeued.Phase != nil || requeued.DownloadedBytes != nil || requeued.Attempts != 1 {
+		t.Fatalf("graceful requeue: %+v %v", requeued, err)
+	}
+	if err := s.RequeueRunning(ctx, claimed.ID); !errors.Is(err, ErrInvalidTransition) {
+		t.Fatalf("待機中の再復帰: %v", err)
+	}
+}
+
 func TestRejectedTransitions(t *testing.T) {
 	pool := testPool(t, true)
 	s := New(pool)