Harden prepare and transcribe transitions

internal/stage/transcribe.go

@@ -112,6 +112,7 @@ func (transcribeStage) Run(ctx context.Context, env *Env, m *manifest.Manifest)
 		jobCh     = make(chan job)
 		mu        sync.Mutex
 		firstErr  error
+		completed int
 		perFile   = map[string]map[string]any{}
 		outputRef = map[string]artifacts.Ref{}
 	)
@@ -175,6 +176,7 @@ func (transcribeStage) Run(ctx context.Context, env *Env, m *manifest.Manifest)
 				SessionID:    sessionID,
 				AbsolutePath: j.outPath,
 			}
+			completed++
 			mu.Unlock()
 		}
 	}
@@ -184,12 +186,14 @@ func (transcribeStage) Run(ctx context.Context, env *Env, m *manifest.Manifest)
 		go worker()
 	}
 
+	dispatched := 0
 dispatch:
 	for _, j := range jobs {
 		select {
 		case <-stageCtx.Done():
 			break dispatch
 		case jobCh <- j:
+			dispatched++
 		}
 	}
 	close(jobCh)
@@ -198,6 +202,12 @@ dispatch:
 	if firstErr != nil {
 		return nil, firstErr
 	}
+	if err := ctx.Err(); err != nil {
+		return nil, fmt.Errorf("transcribe: canceled after dispatching %d of %d audio jobs and completing %d: %w", dispatched, len(jobs), completed, err)
+	}
+	if completed != len(jobs) {
+		return nil, fmt.Errorf("transcribe: completed %d of %d planned audio jobs after dispatching %d", completed, len(jobs), dispatched)
+	}
 
 	speakers := make([]string, 0, len(perFile))
 	for speaker := range perFile {