chore(jobs): align log keys + add prune no-op test + down-migration comment

Cross-cutting review polish:
- worker.go: id/type → job_id/job_type; one stray attempts → attempt for
  consistency with the other 4 sites in the same file.
- runners/workspace_fetch.go: ws_id → workspace_id (matches the dispatched
  notify.Message metadata key).
- runners/worktree_prune.go: id → worktree_id (same reason).
- runners/worktree_prune_test.go: add TestWorktreePrune_NoRowsIsNoOp for
  symmetry with the no-op tests in the other 4 runner test files.
- migrations/0005_jobs.down.sql: comment that DROP TABLE jobs cascades to
  drop the three idx_jobs_* indexes automatically.

internal/jobs/runners/workspace_fetch.go

@@ -75,7 +75,7 @@ func (r *WorkspaceFetch) Run(ctx context.Context) {
 func (r *WorkspaceFetch) fetchOne(ctx context.Context, t WorkspaceFetchTarget) {
 	ok, err := r.repo.MarkSyncing(ctx, t.ID)
 	if err != nil {
-		r.log.Error("workspace_fetch.mark_syncing", "ws_id", t.ID, "err", err.Error())
+		r.log.Error("workspace_fetch.mark_syncing", "workspace_id", t.ID, "err", err.Error())
 		return
 	}
 	if !ok {
@@ -85,7 +85,7 @@ func (r *WorkspaceFetch) fetchOne(ctx context.Context, t WorkspaceFetchTarget) {
 	if fetchErr := r.gitr.Fetch(ctx, t.MainPath, t.ID); fetchErr != nil {
 		msg := truncate(fetchErr.Error(), 2000)
 		if err := r.repo.MarkFetchResult(ctx, t.ID, false, msg); err != nil {
-			r.log.Error("workspace_fetch.mark_fail", "ws_id", t.ID, "err", err.Error())
+			r.log.Error("workspace_fetch.mark_fail", "workspace_id", t.ID, "err", err.Error())
 			return
 		}
 		if derr := r.disp.Dispatch(ctx, notify.Message{
@@ -101,13 +101,13 @@ func (r *WorkspaceFetch) fetchOne(ctx context.Context, t WorkspaceFetchTarget) {
 			},
 			CreatedAt: time.Now().UTC(),
 		}); derr != nil {
-			r.log.Error("workspace_fetch.dispatch", "ws_id", t.ID, "err", derr.Error())
+			r.log.Error("workspace_fetch.dispatch", "workspace_id", t.ID, "err", derr.Error())
 		}
-		r.log.Warn("workspace_fetch.failed", "ws_id", t.ID, "err", msg)
+		r.log.Warn("workspace_fetch.failed", "workspace_id", t.ID, "err", msg)
 		return
 	}
 	if err := r.repo.MarkFetchResult(ctx, t.ID, true, ""); err != nil {
-		r.log.Error("workspace_fetch.mark_ok", "ws_id", t.ID, "err", err.Error())
+		r.log.Error("workspace_fetch.mark_ok", "workspace_id", t.ID, "err", err.Error())
 	}
 }
 

internal/jobs/runners/worktree_prune.go

@@ -75,7 +75,7 @@ func (r *WorktreePrune) warningPhase(ctx context.Context) {
 	}
 	for _, w := range rows {
 		if err := r.repo.MarkPruneWarning(ctx, w.ID); err != nil {
-			r.log.Error("worktree_prune.mark_warning", "id", w.ID, "err", err.Error())
+			r.log.Error("worktree_prune.mark_warning", "worktree_id", w.ID, "err", err.Error())
 			continue
 		}
 		if derr := r.disp.Dispatch(ctx, notify.Message{
@@ -90,7 +90,7 @@ func (r *WorktreePrune) warningPhase(ctx context.Context) {
 			},
 			CreatedAt: time.Now().UTC(),
 		}); derr != nil {
-			r.log.Error("worktree_prune.dispatch", "id", w.ID, "err", derr.Error())
+			r.log.Error("worktree_prune.dispatch", "worktree_id", w.ID, "err", derr.Error())
 		}
 	}
 }
@@ -109,14 +109,14 @@ func (r *WorktreePrune) executionPhase(ctx context.Context) {
 			continue
 		}
 		if rmErr := r.gitr.WorktreeRemove(ctx, started.MainPath, started.Path); rmErr != nil {
-			r.log.Error("worktree_prune.remove_failed", "id", w.ID, "err", rmErr.Error())
+			r.log.Error("worktree_prune.remove_failed", "worktree_id", w.ID, "err", rmErr.Error())
 			if rbErr := r.repo.FinishPruneRollback(ctx, w.ID); rbErr != nil {
-				r.log.Error("worktree_prune.rollback", "id", w.ID, "err", rbErr.Error())
+				r.log.Error("worktree_prune.rollback", "worktree_id", w.ID, "err", rbErr.Error())
 			}
 			continue
 		}
 		if err := r.repo.FinishPruneSuccess(ctx, w.ID); err != nil {
-			r.log.Error("worktree_prune.finish_success", "id", w.ID, "err", err.Error())
+			r.log.Error("worktree_prune.finish_success", "worktree_id", w.ID, "err", err.Error())
 		}
 	}
 }

internal/jobs/runners/worktree_prune_test.go

@@ -155,6 +155,23 @@ func TestWorktreePrune_ExecutionFailureRollsBack(t *testing.T) {
 	assert.Equal(t, "rollback", repo.finalized[id])
 }
 
+func TestWorktreePrune_NoRowsIsNoOp(t *testing.T) {
+	t.Parallel()
+	repo := &fakeWorktreeRepo{} // both lists nil
+	gitr := &fakePruner{}
+	disp := &recordingDispatcher{}
+	cfg := runners.WorktreePruneConfig{IdleThreshold: 7 * 24 * time.Hour, WarningLead: 3 * 24 * time.Hour}
+
+	r := runners.NewWorktreePrune(repo, gitr, disp, cfg, discardLogger())
+	r.Run(context.Background())
+
+	assert.Empty(t, repo.markedWarning)
+	assert.Empty(t, repo.tryStartCalled)
+	assert.Empty(t, repo.finalized)
+	assert.Zero(t, gitr.calls)
+	assert.Empty(t, disp.msgs)
+}
+
 func TestWorktreePrune_CASLostSkipsSilently(t *testing.T) {
 	t.Parallel()
 	id := uuid.New()