diff --git a/AGENTS.md b/AGENTS.md
index dde5ed9..d29d34c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -69,7 +69,7 @@ Commands registered on the **`docgen`** CLI include:
 - **`gui`** — desktop window over the same Vue/Flask UI (`pip install 'docgen[gui]'` for pywebview). ``--smoke`` is a headless HTTP check. PyInstaller spec: ``packaging/docgen-gui.spec``. Frozen apps resolve templates/static/benchmark JSON via ``docgen.resources``.
 - **`freeze`** — ``docgen freeze`` builds the **`docgen-gui`** onedir (`pip install 'docgen[packaging]'`). Optional ``--smoke`` runs the binary headless. Do not run a full freeze in routine pytest; set ``DOCGEN_FREEZE_SMOKE=1`` for the optional test.
 - **`tts`** — text-to-speech for segment files (OpenAI or xAI `/v1/tts`).
-- **`timestamps`** — word/segment timing (`timing.json`). Default engine **`local`** aligns the known narration text against the mp3 offline (ffmpeg silencedetect, no API); **`--engine whisper`** uses OpenAI whisper-1 or xAI `/v1/stt` when `ai.provider` is grok. Both emit the same Whisper-shaped blocks. Failed ffmpeg silencedetect raises `AlignmentError` (empty stderr is not treated as full-span speech). OpenAI whisper-1 word/segment `start`/`end` must be finite JSON numbers (bool/NaN raise `AIError`). Grok `/v1/stt` rejects empty word tokens and inverted `end < start` intervals (`AIError`).
+- **`timestamps`** — word/segment timing (`timing.json`). Default engine **`local`** aligns the known narration text against the mp3 offline (ffmpeg silencedetect, no API); **`--engine whisper`** uses OpenAI whisper-1 or xAI `/v1/stt` when `ai.provider` is grok. Both emit the same Whisper-shaped blocks. Failed ffmpeg silencedetect raises `AlignmentError` (empty stderr is not treated as full-span speech). OpenAI whisper-1 word/segment `start`/`end` must be finite JSON numbers (bool/NaN raise `AIError`). Grok `/v1/stt` rejects empty word tokens and inverted `end < start` intervals (`AIError`). Empty ``segments.all`` raises ``TimestampError`` (same as TTS) and does not leave a stale ``timing.json`` as success.
 - **`image-generate`** — render scene-spec **image elements** (`image:` + `prompt:` boxes) via OpenAI Images or xAI Imagine into the bundle (also runs for missing assets inside `generate-all`).
 - **`manim`** — render Manim scenes declared in config.
 - **`compose`** — mux narration audio with visual sources via ffmpeg. A ``type: mixed`` row raises ``ComposeError`` if any listed source is missing (no silent subset mux).
diff --git a/README.md b/README.md
index 7bdaba5..cff5127 100644
--- a/README.md
+++ b/README.md
@@ -40,7 +40,9 @@ If you still need the legacy behaviour, pin a pre-removal commit
   OpenAI `whisper-1` or xAI `/v1/stt` when the provider is Grok. Both engines
   write the same `timing.json` shape. OpenAI whisper-1 word/segment `start`/`end`
   must be finite JSON numbers (bool/NaN raise `AIError`). Grok `/v1/stt` rejects
-  empty word tokens and inverted `end < start` intervals (`AIError`).
+  empty word tokens and inverted `end < start` intervals (`AIError`). Empty
+  `segments.all` raises `TimestampError` (same as TTS) and does not leave a
+  stale `timing.json` as success.
 - **Manim animations (default: declarative scene specs)** — primary visual surface.
   Prefer **`animations/specs/*.scene.yaml`** via **`docgen scene-spec-generate`**
   + **`scene-compile`**. On **`generate-all`**, if no specs exist yet, the pipeline
@@ -238,7 +240,7 @@ docgen --repo /path/to/your-project generate-all
 | `docgen gui [--view benchmark] [--browser] [--smoke]` | Desktop GUI (Vue + Flask). Install `docgen[gui]` for a pywebview window; `--browser` uses the system browser; `--smoke` is a headless HTTP check |
 | `docgen freeze [--dist DIR] [--smoke]` | PyInstaller onedir for **`docgen-gui` only** (`pip install 'docgen[packaging]'`). Not the full Manim CLI |
 | `docgen tts [--segment 01] [--dry-run]` | Generate TTS audio |
-| `docgen timestamps [--engine local\|whisper]` | Extract word/segment timestamps from TTS audio → `timing.json` (default `local`: offline narration-text alignment; `whisper`: OpenAI transcription) |
+| `docgen timestamps [--engine local\|whisper]` | Extract word/segment timestamps from TTS audio → `timing.json` (default `local`: offline narration-text alignment; `whisper`: OpenAI transcription). Empty `segments.all` is `TimestampError` (stale `timing.json` is not success) |
 | `docgen image-generate [--segment 01 \| --all \| --spec PATH] [--force] [--dry-run] [--model …] [--size …]` | Generate scene-spec image assets (`image:` + `prompt:` boxes) via the OpenAI Images API into the bundle |
 | `docgen manim [--scene StackDAGScene]` | Render Manim animations |
 | `docgen compose [01 02 03] [--ffmpeg-timeout 900]` | Compose segments (audio + video) |
diff --git a/src/docgen/timestamps.py b/src/docgen/timestamps.py
index 88f4626..d50dd67 100644
--- a/src/docgen/timestamps.py
+++ b/src/docgen/timestamps.py
@@ -229,8 +229,9 @@ def extract_all(self, engine: str | None = None) -> None:
         """Extract timestamps for ``segments.all`` and write timing.json.
 
         Walks configured segment ids via :meth:`Config.find_segment_asset` (no
-        ``*.mp3`` glob). Missing audio for a listed segment is an error. With
-        no ``segments.all`` entries, existing ``timing.json`` is left unchanged.
+        ``*.mp3`` glob). Missing audio for a listed segment is an error. An
+        empty ``segments.all`` raises :class:`TimestampError` (same as TTS)
+        and does not treat an existing ``timing.json`` as success.
 
         Successful runs **merge** stems into the existing file (same as the
         wizard per-segment timestamps step) so extra keys not in
@@ -254,8 +255,10 @@ def extract_all(self, engine: str | None = None) -> None:
 
         seg_ids = [str(s) for s in self.config.segments_all]
         if not seg_ids:
-            print("[timestamps] segments.all is empty; leaving timing.json unchanged")
-            return
+            raise TimestampError(
+                "segments.all is empty — add segment ids in docgen.yaml "
+                "(or hints + yaml-generate) before timestamps"
+            )
 
         missing: list[str] = []
         jobs: list[tuple[str, Path]] = []
diff --git a/tests/test_timestamps_local.py b/tests/test_timestamps_local.py
index b1388d0..8279d73 100644
--- a/tests/test_timestamps_local.py
+++ b/tests/test_timestamps_local.py
@@ -107,16 +107,20 @@ def test_no_mp3s_fails_when_segments_listed(self, cfg) -> None:
             TimestampExtractor(cfg).extract_all()
         assert json.loads(out.read_text(encoding="utf-8")) == {"keep": True}
 
-    def test_empty_segments_all_leaves_existing_timing_json(self, tmp_path) -> None:
+    def test_empty_segments_all_stale_timing_json_raises(self, tmp_path) -> None:
         (tmp_path / "docgen.yaml").write_text(
             yaml.dump({"segments": {"all": []}}), encoding="utf-8"
         )
         cfg = Config.from_yaml(tmp_path / "docgen.yaml")
         out = cfg.animations_dir / "timing.json"
         out.parent.mkdir(parents=True, exist_ok=True)
-        out.write_text('{"keep": true}\n', encoding="utf-8")
-        TimestampExtractor(cfg).extract_all()
-        assert json.loads(out.read_text(encoding="utf-8")) == {"keep": True}
+        stale = {"keep": True, "legacy-stem": {"text": "stale"}}
+        out.write_text(json.dumps(stale) + "\n", encoding="utf-8")
+        from docgen.timestamps import TimestampError
+
+        with pytest.raises(TimestampError, match="segments.all is empty"):
+            TimestampExtractor(cfg).extract_all()
+        assert json.loads(out.read_text(encoding="utf-8")) == stale
 
     def test_heading_only_narration_fails_loud(self, cfg, monkeypatch) -> None:
         _fake_audio_env(monkeypatch)