diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 06c6d5a..324a1b7 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -1,6 +1,6 @@
 # Implementation Plan: Shared Stage Checkpoint Mechanics
 
-Status: Implementation in progress; Stages 1-2 complete.
+Status: Implementation in progress; Stages 1-3 complete.
 
 ## Scope and Authority
 
@@ -229,7 +229,17 @@ selection, and failure behavior remain unchanged.
 
 ## Stage 3: Migrate Transcribe and Remove Duplicate Machinery
 
-Status: Pending.
+Status: Complete.
+
+Completion marker (2026-09-22): Delegated transcription's locked checkpoint
+operation to the shared helper while retaining typed validation, direct-call
+record initialization, stage timestamp updates, post-save working collection
+refresh, and the existing caller-owned mutex and failure latch. Removed the
+duplicate production manifest clone; the read-only resume assertion now uses
+the shared bounded snapshot. Existing real-store, concurrency, force/retry,
+interruption, aggregate-repair, and zero-sized-audio coverage passed unchanged.
+Verified with `go test ./internal/stage ./internal/app ./internal/manifest`,
+`go test -race ./internal/stage ./internal/app`, and `git diff --check`.
 
 Preparation: `internal/stage/transcribe_execution_state.go`, `transcribe.go`,
 `transcribe_resume.go`, `transcribe_checkpoint_test.go`,
diff --git a/internal/stage/transcribe_execution_state.go b/internal/stage/transcribe_execution_state.go
index 640035c..702aa44 100644
--- a/internal/stage/transcribe_execution_state.go
+++ b/internal/stage/transcribe_execution_state.go
@@ -156,39 +156,30 @@ func (state *transcribeExecutionState) checkpointCollectionLocked(
 		return fmt.Errorf("validate transcribe speaker collection: %w", err)
 	}
 
-	candidate := cloneManifestForTranscribeCheckpoint(state.manifest)
-	if candidate.Stages == nil {
-		candidate.Stages = make(map[string]*manifest.StageRecord)
-	}
-	record := candidate.Stages["transcribe"]
-	if record == nil {
-		now := time.Now().UTC()
-		record = &manifest.StageRecord{
-			Name: "transcribe", Status: manifest.StatusRunning, CreatedAt: now, UpdatedAt: now,
-		}
-		candidate.Stages["transcribe"] = record
-	}
-	record.TranscribeStateVersion = manifest.TranscribeStateContractVersion
-	record.TranscribeSpeakers = manifest.CloneTranscribeSpeakerCollection(records)
-	record.UpdatedAt = time.Now().UTC()
-	if err := state.env.ManifestStore.Save(ctx, state.paths.ManifestPath, candidate); err != nil {
-		return fmt.Errorf("save session manifest %q: %w", state.paths.ManifestPath, err)
+	missingRecord := transcribeStageRecord(state.manifest) == nil
+	if err := checkpointStageCollection(
+		ctx,
+		state.env.ManifestStore,
+		state.paths.ManifestPath,
+		state.manifest,
+		"transcribe",
+		func(record *manifest.StageRecord) error {
+			if missingRecord {
+				now := time.Now().UTC()
+				*record = manifest.StageRecord{
+					Name: "transcribe", Status: manifest.StatusRunning, CreatedAt: now, UpdatedAt: now,
+				}
+			}
+			record.TranscribeStateVersion = manifest.TranscribeStateContractVersion
+			record.TranscribeSpeakers = manifest.CloneTranscribeSpeakerCollection(records)
+			record.UpdatedAt = time.Now().UTC()
+			return nil
+		},
+	); err != nil {
+		return err
 	}
 
 	live := transcribeStageRecord(state.manifest)
-	if live == nil {
-		live = &manifest.StageRecord{}
-		if state.manifest.Stages == nil {
-			state.manifest.Stages = make(map[string]*manifest.StageRecord)
-		}
-		state.manifest.Stages["transcribe"] = live
-	}
-	live.TranscribeStateVersion = candidate.Stages["transcribe"].TranscribeStateVersion
-	live.TranscribeSpeakers = manifest.CloneTranscribeSpeakerCollection(
-		candidate.Stages["transcribe"].TranscribeSpeakers,
-	)
-	live.UpdatedAt = candidate.Stages["transcribe"].UpdatedAt
-	state.manifest.UpdatedAt = candidate.UpdatedAt
 	state.records = manifest.CloneTranscribeSpeakerCollection(live.TranscribeSpeakers)
 	return nil
 }
@@ -259,27 +250,6 @@ func transcribeStageRecord(m *manifest.Manifest) *manifest.StageRecord {
 	return m.Stages["transcribe"]
 }
 
-func cloneManifestForTranscribeCheckpoint(source *manifest.Manifest) *manifest.Manifest {
-	clone := *source
-	clone.Inputs = append([]manifest.InputRecord(nil), source.Inputs...)
-	clone.Artifacts = append([]manifest.ArtifactRecord(nil), source.Artifacts...)
-	clone.Stages = make(map[string]*manifest.StageRecord, len(source.Stages))
-	for name, sourceRecord := range source.Stages {
-		if sourceRecord == nil {
-			clone.Stages[name] = nil
-			continue
-		}
-		record := *sourceRecord
-		record.Outputs = append([]manifest.ArtifactRecord(nil), sourceRecord.Outputs...)
-		record.Logs = append([]string(nil), sourceRecord.Logs...)
-		record.GeneratedConfigs = append([]string(nil), sourceRecord.GeneratedConfigs...)
-		record.TranscribeSpeakers = manifest.CloneTranscribeSpeakerCollection(sourceRecord.TranscribeSpeakers)
-		record.AnalyzeArtifacts = manifest.CloneAnalyzeArtifactCollection(sourceRecord.AnalyzeArtifacts)
-		clone.Stages[name] = &record
-	}
-	return &clone
-}
-
 func cloneStringAnyMap(source map[string]any) map[string]any {
 	if source == nil {
 		return nil
diff --git a/internal/stage/transcribe_reconciliation_test.go b/internal/stage/transcribe_reconciliation_test.go
index 98d42be..56da6f1 100644
--- a/internal/stage/transcribe_reconciliation_test.go
+++ b/internal/stage/transcribe_reconciliation_test.go
@@ -58,7 +58,7 @@ func TestTranscribeResumeAcceptsEquivalentOutputsAndInspectsRemovalReadOnly(t *t
 		t.Fatalf("equivalent aggregate: %#v, %v", validation, err)
 	}
 	m.Inputs = slices.DeleteFunc(m.Inputs, func(in manifest.InputRecord) bool { return filepath.Base(in.Path) == "bob.flac" })
-	before := cloneManifestForTranscribeCheckpoint(m)
+	before := cloneManifestForCheckpoint(m)
 	validation, err = (transcribeStage{}).ValidateResume(context.Background(), env, m)
 	if err != nil || validation.Resumable {
 		t.Fatalf("removed speaker: %#v, %v", validation, err)