diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
new file mode 100644
index 0000000..32544c7
--- /dev/null
+++ b/.github/pull_request_template.md
@@ -0,0 +1,23 @@
+## Summary
+
+Describe what changed and why.
+
+## Spec Link (Required For Feature Changes)
+
+- Spec file in `docs/specs/`: <!-- e.g. docs/specs/2026-04-15-speed-adjustment.md -->
+
+## Acceptance Criteria Checklist
+
+- [ ] Acceptance criteria reviewed against the linked spec
+- [ ] User-visible behavior verified for this change
+- [ ] Backward compatibility impact assessed
+
+## Validation
+
+- [ ] `./scripts/validate-all.sh` passes locally
+- [ ] Added/updated tests for changed behavior
+
+## Risk And Rollback
+
+- Risk level: Low / Medium / High
+- Rollback plan:
diff --git a/.github/workflows/validate-all.yml b/.github/workflows/validate-all.yml
new file mode 100644
index 0000000..9221028
--- /dev/null
+++ b/.github/workflows/validate-all.yml
@@ -0,0 +1,58 @@
+name: Validate All
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  validate-all:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: npm
+          cache-dependency-path: |
+            frontend/package-lock.json
+            package-lock.json
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Enforce feature spec policy (PR only)
+        if: github.event_name == 'pull_request'
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+        run: ./scripts/check-feature-spec.sh
+
+      - name: Install frontend dependencies
+        run: |
+          cd frontend
+          npm install
+
+      - name: Run validate-all
+        env:
+          SKIP_BACKEND_IMPORT_SMOKE: '1'
+        run: ./scripts/validate-all.sh
+
+      - name: Collect diagnostics on failure
+        if: failure()
+        run: ./scripts/collect-diagnostics.sh
+
+      - name: Upload diagnostics artifact
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: diagnostics
+          path: .diagnostics
diff --git a/FEATURES.md b/FEATURES.md
index 8de3df4..c63a818 100644
--- a/FEATURES.md
+++ b/FEATURES.md
@@ -18,7 +18,7 @@ Features are grouped by priority. Check off items as they are implemented.
 
 - [x] [#006] **Volume / gain control** — per-selection or global audio gain slider. Every editor has this. Descript users constantly complain it's missing. Backend: `ffmpeg -af volume=Xdb`.
 
-- [ ] [#007] **Speed adjustment** — slow down or speed up a selection or the whole clip. Backend: `ffmpeg -filter:v setpts` + `atempo`. Common use case: slightly speed up boring sections.
+- [ ] [#007] **Speed adjustment (4th zone type)** — add speed zones as the fourth editable timeline/transcript zone type (after cut, mute, gain), allowing slow/fast playback per range or globally. Backend: `ffmpeg -filter:v setpts` + `atempo`. Common use case: slightly speed up boring sections.
 
 - [ ] [#008] **Cut preview** — before committing a delete, play what the audio will sound like with that section removed (pre-listen across the edit point). Pure frontend using Web Audio API — splice the AudioBuffer and play the join.
 
diff --git a/backend/tests/__init__.py b/backend/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/backend/tests/test_cache_utils.py b/backend/tests/test_cache_utils.py
new file mode 100644
index 0000000..b5cd759
--- /dev/null
+++ b/backend/tests/test_cache_utils.py
@@ -0,0 +1,57 @@
+import tempfile
+import time
+import unittest
+from pathlib import Path
+
+from backend.utils import cache as cache_utils
+
+
+class CacheUtilsTests(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmp_dir = tempfile.TemporaryDirectory()
+        self._old_cache_dir = cache_utils.CACHE_DIR
+        cache_utils.CACHE_DIR = Path(self._tmp_dir.name) / "cache"
+
+        self._work_dir = Path(self._tmp_dir.name) / "work"
+        self._work_dir.mkdir(parents=True, exist_ok=True)
+        self._src_file = self._work_dir / "sample.txt"
+        self._src_file.write_text("hello", encoding="utf-8")
+
+    def tearDown(self) -> None:
+        cache_utils.CACHE_DIR = self._old_cache_dir
+        self._tmp_dir.cleanup()
+
+    def test_get_file_hash_returns_none_for_missing_file(self) -> None:
+        missing = self._work_dir / "missing.txt"
+        self.assertIsNone(cache_utils.get_file_hash(missing))
+
+    def test_save_and_load_round_trip(self) -> None:
+        payload = {"value": 123, "ok": True}
+        saved = cache_utils.save_to_cache(self._src_file, payload, model="m1", operation="transcribe")
+        self.assertTrue(saved)
+
+        loaded = cache_utils.load_from_cache(self._src_file, model="m1", operation="transcribe")
+        self.assertEqual(payload, loaded)
+
+    def test_load_from_cache_respects_max_age(self) -> None:
+        payload = {"value": 999}
+        self.assertTrue(cache_utils.save_to_cache(self._src_file, payload, operation="transcribe"))
+
+        time.sleep(0.02)
+        expired = cache_utils.load_from_cache(self._src_file, operation="transcribe", max_age=0.001)
+        self.assertIsNone(expired)
+
+    def test_clear_cache_deletes_files(self) -> None:
+        self.assertTrue(cache_utils.save_to_cache(self._src_file, {"a": 1}, operation="transcribe"))
+        self.assertTrue(cache_utils.save_to_cache(self._src_file, {"a": 2}, operation="summarize"))
+
+        deleted_count = cache_utils.clear_cache()
+        self.assertGreaterEqual(deleted_count, 1)
+
+        size_bytes, file_count = cache_utils.get_cache_size()
+        self.assertEqual(size_bytes, 0)
+        self.assertEqual(file_count, 0)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/backend/tests/test_router_contracts.py b/backend/tests/test_router_contracts.py
new file mode 100644
index 0000000..057ee3b
--- /dev/null
+++ b/backend/tests/test_router_contracts.py
@@ -0,0 +1,451 @@
+import unittest
+from unittest.mock import patch
+from pathlib import Path
+from tempfile import TemporaryDirectory
+import os
+from types import SimpleNamespace
+
+from fastapi.testclient import TestClient
+
+from backend.main import app
+from routers import audio as audio_router
+
+
+class RouterContractTests(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls) -> None:
+        cls.client = TestClient(app)
+
+    def setUp(self) -> None:
+        audio_router._waveform_cache.clear()
+
+    def test_health_endpoint(self) -> None:
+        res = self.client.get("/health")
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json(), {"status": "ok"})
+
+    def test_file_endpoint_full_content(self) -> None:
+        with TemporaryDirectory() as tmp:
+            file_path = Path(tmp) / "sample.wav"
+            file_path.write_bytes(b"abcdefghij")
+
+            res = self.client.get("/file", params={"path": str(file_path)})
+
+            self.assertEqual(res.status_code, 200)
+            self.assertEqual(res.content, b"abcdefghij")
+            self.assertEqual(res.headers.get("accept-ranges"), "bytes")
+
+    def test_file_endpoint_range_request(self) -> None:
+        with TemporaryDirectory() as tmp:
+            file_path = Path(tmp) / "sample.wav"
+            file_path.write_bytes(b"abcdefghij")
+
+            res = self.client.get(
+                "/file",
+                params={"path": str(file_path)},
+                headers={"Range": "bytes=2-5"},
+            )
+
+            self.assertEqual(res.status_code, 206)
+            self.assertEqual(res.content, b"cdef")
+            self.assertEqual(res.headers.get("content-range"), "bytes 2-5/10")
+
+    def test_file_endpoint_missing_file(self) -> None:
+        res = self.client.get("/file", params={"path": "/tmp/does-not-exist.wav"})
+
+        self.assertEqual(res.status_code, 404)
+        self.assertIn("File not found", res.json()["detail"])
+
+    @patch("routers.audio.subprocess.run")
+    def test_audio_waveform_cache_miss_then_hit(self, mock_subprocess_run) -> None:
+        with TemporaryDirectory() as tmp:
+            media_file = Path(tmp) / "input.mp4"
+            media_file.write_bytes(b"fake-media")
+
+            def fake_ffmpeg(cmd, capture_output, text):
+                out_path = Path(cmd[-1])
+                out_path.parent.mkdir(parents=True, exist_ok=True)
+                out_path.write_bytes(b"fake-wav")
+                return SimpleNamespace(returncode=0, stderr="")
+
+            mock_subprocess_run.side_effect = fake_ffmpeg
+
+            res1 = self.client.get("/audio/waveform", params={"path": str(media_file)})
+            self.assertEqual(res1.status_code, 200)
+            self.assertTrue(res1.headers.get("content-type", "").startswith("audio/wav"))
+
+            res2 = self.client.get("/audio/waveform", params={"path": str(media_file)})
+            self.assertEqual(res2.status_code, 200)
+            self.assertTrue(res2.headers.get("content-type", "").startswith("audio/wav"))
+
+            self.assertEqual(mock_subprocess_run.call_count, 1)
+
+    @patch("routers.audio.subprocess.run")
+    def test_audio_waveform_ffmpeg_failure_returns_500(self, mock_subprocess_run) -> None:
+        with TemporaryDirectory() as tmp:
+            media_file = Path(tmp) / "input.mp4"
+            media_file.write_bytes(b"fake-media")
+
+            mock_subprocess_run.return_value = SimpleNamespace(returncode=1, stderr="ffmpeg failed")
+
+            res = self.client.get("/audio/waveform", params={"path": str(media_file)})
+
+            self.assertEqual(res.status_code, 500)
+            self.assertIn("Failed to extract audio", res.json()["detail"])
+
+    @patch("routers.ai.detect_filler_words")
+    def test_ai_filler_removal_contract(self, mock_detect_filler_words) -> None:
+        mock_detect_filler_words.return_value = {
+            "wordIndices": [2, 5],
+            "fillerWords": [
+                {"index": 2, "word": "um", "reason": "filler"},
+                {"index": 5, "word": "uh", "reason": "filler"},
+            ],
+        }
+
+        payload = {
+            "transcript": "Hello um world uh",
+            "words": [
+                {"index": 0, "word": "Hello"},
+                {"index": 1, "word": "um"},
+                {"index": 2, "word": "world"},
+            ],
+            "provider": "ollama",
+            "model": "llama3",
+        }
+        res = self.client.post("/ai/filler-removal", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertIn("wordIndices", res.json())
+        mock_detect_filler_words.assert_called_once()
+
+    @patch("routers.ai.detect_filler_words")
+    def test_ai_filler_removal_error_returns_500(self, mock_detect_filler_words) -> None:
+        mock_detect_filler_words.side_effect = RuntimeError("ai-filler-fail")
+
+        payload = {
+            "transcript": "Hello world",
+            "words": [{"index": 0, "word": "Hello"}],
+            "provider": "ollama",
+        }
+        res = self.client.post("/ai/filler-removal", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "ai-filler-fail")
+
+    @patch("routers.ai.create_clip_suggestion")
+    def test_ai_create_clip_contract(self, mock_create_clip_suggestion) -> None:
+        mock_create_clip_suggestion.return_value = {
+            "title": "Best Moment",
+            "startWordIndex": 10,
+            "endWordIndex": 40,
+            "startTime": 12.3,
+            "endTime": 48.8,
+            "reason": "Strong hook",
+        }
+
+        payload = {
+            "transcript": "Long transcript...",
+            "words": [{"index": 0, "word": "hello"}],
+            "provider": "ollama",
+            "target_duration": 45,
+        }
+        res = self.client.post("/ai/create-clip", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json()["title"], "Best Moment")
+        mock_create_clip_suggestion.assert_called_once()
+
+    @patch("routers.ai.create_clip_suggestion")
+    def test_ai_create_clip_error_returns_500(self, mock_create_clip_suggestion) -> None:
+        mock_create_clip_suggestion.side_effect = RuntimeError("ai-clip-fail")
+
+        payload = {
+            "transcript": "Hello world",
+            "words": [{"index": 0, "word": "hello"}],
+            "provider": "ollama",
+        }
+        res = self.client.post("/ai/create-clip", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "ai-clip-fail")
+
+    @patch("routers.ai.AIProvider.list_ollama_models")
+    def test_ai_ollama_models_contract(self, mock_list_ollama_models) -> None:
+        mock_list_ollama_models.return_value = ["llama3", "qwen2.5"]
+
+        res = self.client.get("/ai/ollama-models?base_url=http://localhost:11434")
+
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json(), {"models": ["llama3", "qwen2.5"]})
+        mock_list_ollama_models.assert_called_once_with("http://localhost:11434")
+
+    @patch("routers.ai.AIProvider.list_ollama_models")
+    def test_ai_ollama_models_unhandled_error_returns_500(self, mock_list_ollama_models) -> None:
+        mock_list_ollama_models.side_effect = RuntimeError("ollama-unreachable")
+
+        local_client = TestClient(app, raise_server_exceptions=False)
+        res = local_client.get("/ai/ollama-models")
+
+        self.assertEqual(res.status_code, 500)
+
+    @patch("routers.transcribe.transcribe_audio")
+    def test_transcribe_success(self, mock_transcribe) -> None:
+        mock_transcribe.return_value = {"words": [], "segments": [], "language": "en"}
+
+        payload = {
+            "file_path": "/tmp/input.wav",
+            "model": "base",
+            "use_gpu": False,
+            "use_cache": True,
+        }
+        res = self.client.post("/transcribe", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json(), {"words": [], "segments": [], "language": "en"})
+        mock_transcribe.assert_called_once()
+
+    @patch("routers.transcribe.diarize_and_label")
+    @patch("routers.transcribe.transcribe_audio")
+    def test_transcribe_with_diarization(self, mock_transcribe, mock_diarize) -> None:
+        mock_transcribe.return_value = {"words": [{"word": "hi", "start": 0.0, "end": 0.2}], "segments": []}
+        mock_diarize.return_value = {"words": [{"word": "hi", "start": 0.0, "end": 0.2, "speaker": "SPEAKER_00"}], "segments": []}
+
+        payload = {
+            "file_path": "/tmp/input.wav",
+            "model": "base",
+            "diarize": True,
+            "hf_token": "hf_xxx",
+            "num_speakers": 2,
+        }
+        res = self.client.post("/transcribe", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertIn("words", res.json())
+        mock_transcribe.assert_called_once()
+        mock_diarize.assert_called_once()
+
+    @patch("routers.transcribe.transcribe_audio")
+    def test_transcribe_file_not_found_returns_404(self, mock_transcribe) -> None:
+        mock_transcribe.side_effect = FileNotFoundError("missing")
+
+        payload = {
+            "file_path": "/tmp/missing.wav",
+            "model": "base",
+        }
+        res = self.client.post("/transcribe", json=payload)
+
+        self.assertEqual(res.status_code, 404)
+        self.assertIn("File not found", res.json()["detail"])
+
+    @patch("routers.transcribe.transcribe_audio")
+    def test_transcribe_runtime_failure_returns_500(self, mock_transcribe) -> None:
+        mock_transcribe.side_effect = RuntimeError("boom")
+
+        payload = {
+            "file_path": "/tmp/in.wav",
+            "model": "base",
+        }
+        res = self.client.post("/transcribe", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "boom")
+
+    @patch("routers.captions.generate_srt")
+    def test_captions_plain_response(self, mock_generate_srt) -> None:
+        mock_generate_srt.return_value = "1\n00:00:00,000 --> 00:00:01,000\nHello\n"
+
+        payload = {
+            "words": [{"word": "Hello", "start": 0.0, "end": 1.0}],
+            "format": "srt",
+        }
+        res = self.client.post("/captions", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertIn("Hello", res.text)
+        mock_generate_srt.assert_called_once()
+
+    @patch("routers.captions.save_captions")
+    @patch("routers.captions.generate_srt")
+    def test_captions_save_output_path(self, mock_generate_srt, mock_save) -> None:
+        mock_generate_srt.return_value = "1\n00:00:00,000 --> 00:00:01,000\nHello\n"
+        mock_save.return_value = "/tmp/out.srt"
+
+        payload = {
+            "words": [{"word": "Hello", "start": 0.0, "end": 1.0}],
+            "format": "srt",
+            "output_path": "/tmp/out.srt",
+        }
+        res = self.client.post("/captions", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json(), {"status": "ok", "output_path": "/tmp/out.srt"})
+        mock_save.assert_called_once()
+
+    def test_captions_unknown_format_returns_400(self) -> None:
+        payload = {
+            "words": [{"word": "Hello", "start": 0.0, "end": 1.0}],
+            "format": "txt",
+        }
+        res = self.client.post("/captions", json=payload)
+
+        self.assertEqual(res.status_code, 400)
+        self.assertIn("Unknown format", res.json()["detail"])
+
+    @patch("routers.captions.generate_srt")
+    def test_captions_internal_error_returns_500(self, mock_generate_srt) -> None:
+        mock_generate_srt.side_effect = RuntimeError("caption-fail")
+
+        payload = {
+            "words": [{"word": "Hello", "start": 0.0, "end": 1.0}],
+            "format": "srt",
+        }
+        res = self.client.post("/captions", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "caption-fail")
+
+    @patch("routers.audio.is_deepfilter_available")
+    @patch("routers.audio.clean_audio")
+    def test_audio_clean_contract(self, mock_clean_audio, mock_is_deepfilter_available) -> None:
+        mock_clean_audio.return_value = "/tmp/cleaned.wav"
+        mock_is_deepfilter_available.return_value = True
+
+        payload = {
+            "input_path": "/tmp/in.wav",
+            "output_path": "/tmp/cleaned.wav",
+        }
+        res = self.client.post("/audio/clean", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        body = res.json()
+        self.assertEqual(body["status"], "ok")
+        self.assertEqual(body["output_path"], "/tmp/cleaned.wav")
+        self.assertEqual(body["engine"], "deepfilternet")
+
+    @patch("routers.audio.clean_audio")
+    def test_audio_clean_error_returns_500(self, mock_clean_audio) -> None:
+        mock_clean_audio.side_effect = RuntimeError("clean-fail")
+
+        payload = {
+            "input_path": "/tmp/in.wav",
+            "output_path": "/tmp/cleaned.wav",
+        }
+        res = self.client.post("/audio/clean", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "clean-fail")
+
+    @patch("routers.audio.detect_silence_ranges")
+    def test_audio_detect_silence_contract(self, mock_detect_silence_ranges) -> None:
+        mock_detect_silence_ranges.return_value = [{"start": 1.2, "end": 2.1, "duration": 0.9}]
+
+        payload = {
+            "input_path": "/tmp/in.wav",
+            "min_silence_ms": 500,
+            "silence_db": -35.0,
+        }
+        res = self.client.post("/audio/detect-silence", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        body = res.json()
+        self.assertEqual(body["status"], "ok")
+        self.assertEqual(body["count"], 1)
+        self.assertEqual(len(body["ranges"]), 1)
+
+    @patch("routers.audio.detect_silence_ranges")
+    def test_audio_detect_silence_error_returns_500(self, mock_detect_silence_ranges) -> None:
+        mock_detect_silence_ranges.side_effect = RuntimeError("silence-fail")
+
+        payload = {
+            "input_path": "/tmp/in.wav",
+            "min_silence_ms": 500,
+            "silence_db": -35.0,
+        }
+        res = self.client.post("/audio/detect-silence", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "silence-fail")
+
+    @patch("routers.audio.is_deepfilter_available")
+    def test_audio_capabilities_contract(self, mock_is_deepfilter_available) -> None:
+        mock_is_deepfilter_available.return_value = False
+
+        res = self.client.get("/audio/capabilities")
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json(), {"deepfilternet_available": False})
+
+    @patch("routers.export.export_stream_copy")
+    def test_export_fast_contract(self, mock_export_stream_copy) -> None:
+        mock_export_stream_copy.return_value = "/tmp/out.mp4"
+
+        payload = {
+            "input_path": "/tmp/in.mp4",
+            "output_path": "/tmp/out.mp4",
+            "keep_segments": [{"start": 0.0, "end": 2.0}],
+            "mode": "fast",
+            "captions": "none",
+        }
+        res = self.client.post("/export", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json(), {"status": "ok", "output_path": "/tmp/out.mp4"})
+        mock_export_stream_copy.assert_called_once()
+
+    @patch("routers.export.save_captions")
+    @patch("routers.export.generate_srt")
+    @patch("routers.export.export_stream_copy")
+    def test_export_sidecar_caption_contract(self, mock_export_stream_copy, mock_generate_srt, mock_save_captions) -> None:
+        mock_export_stream_copy.return_value = "/tmp/out.mp4"
+        mock_generate_srt.return_value = "1\n00:00:00,000 --> 00:00:01,000\nHello\n"
+
+        payload = {
+            "input_path": "/tmp/in.mp4",
+            "output_path": "/tmp/out.mp4",
+            "keep_segments": [{"start": 0.0, "end": 2.0}],
+            "mode": "fast",
+            "captions": "sidecar",
+            "words": [{"word": "Hello", "start": 0.0, "end": 1.0}],
+            "deleted_indices": [],
+        }
+        res = self.client.post("/export", json=payload)
+
+        self.assertEqual(res.status_code, 200)
+        body = res.json()
+        self.assertEqual(body["status"], "ok")
+        self.assertEqual(body["output_path"], "/tmp/out.mp4")
+        self.assertEqual(body["srt_path"], "/tmp/out.srt")
+        mock_save_captions.assert_called_once()
+
+    def test_export_missing_segments_returns_400(self) -> None:
+        payload = {
+            "input_path": "/tmp/in.mp4",
+            "output_path": "/tmp/out.mp4",
+            "keep_segments": [],
+            "mode": "fast",
+            "captions": "none",
+        }
+        res = self.client.post("/export", json=payload)
+
+        self.assertEqual(res.status_code, 400)
+        self.assertIn("No segments to export", res.json()["detail"])
+
+    @patch("routers.export.export_stream_copy")
+    def test_export_runtime_error_returns_500(self, mock_export_stream_copy) -> None:
+        mock_export_stream_copy.side_effect = RuntimeError("export-fail")
+
+        payload = {
+            "input_path": "/tmp/in.mp4",
+            "output_path": "/tmp/out.mp4",
+            "keep_segments": [{"start": 0.0, "end": 2.0}],
+            "mode": "fast",
+            "captions": "none",
+        }
+        res = self.client.post("/export", json=payload)
+
+        self.assertEqual(res.status_code, 500)
+        self.assertEqual(res.json()["detail"], "export-fail")
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/docs/specs/README.md b/docs/specs/README.md
new file mode 100644
index 0000000..b3fa3f8
--- /dev/null
+++ b/docs/specs/README.md
@@ -0,0 +1,18 @@
+# Feature Specs
+
+Place one feature spec document in this folder for each feature or major behavior change.
+
+Use [docs/spec-template.md](../spec-template.md) as the canonical template.
+
+Recommended naming format:
+
+- `YYYY-MM-DD-short-feature-name.md`
+
+Examples:
+
+- `2026-04-15-gain-zones-and-visibility-filters.md`
+- `2026-04-16-speed-adjustment.md`
+
+CI policy:
+
+- Pull requests that change app code are expected to include at least one changed spec file in this folder.
diff --git a/frontend/src/components/ZoneEditor.tsx b/frontend/src/components/ZoneEditor.tsx
new file mode 100644
index 0000000..005b297
--- /dev/null
+++ b/frontend/src/components/ZoneEditor.tsx
@@ -0,0 +1,237 @@
+import { useState } from 'react';
+import { useEditorStore } from '../store/editorStore';
+import { Trash2, Scissors, Volume2, SlidersHorizontal } from 'lucide-react';
+
+export default function ZoneEditor() {
+  const [viewMode, setViewMode] = useState<'all' | 'cut' | 'mute' | 'gain'>('all');
+  
+  const {
+    cutRanges,
+    muteRanges,
+    gainRanges,
+    globalGainDb,
+    setGlobalGainDb,
+    removeCutRange,
+    removeMuteRange,
+    removeGainRange,
+    updateGainRange,
+  } = useEditorStore();
+
+  const totalZones = cutRanges.length + muteRanges.length + gainRanges.length;
+
+  const getZoneTypeColor = (type: 'cut' | 'mute' | 'gain') => {
+    switch (type) {
+      case 'cut':
+        return 'border-red-500/40 bg-red-500/5';
+      case 'mute':
+        return 'border-orange-500/40 bg-orange-500/5';
+      case 'gain':
+        return 'border-amber-500/40 bg-amber-500/5';
+    }
+  };
+
+  return (
+    <div className="p-4 space-y-4">
+      <div className="space-y-2">
+        <div className="space-y-1">
+          <h3 className="text-sm font-semibold flex items-center gap-2">
+            <div className="w-4 h-4 rounded bg-editor-accent/30" />
+            Zone Editor
+          </h3>
+          <p className="text-xs text-editor-text-muted">
+            Manage all timeline zones ({totalZones} total)
+          </p>
+        </div>
+        
+        {/* View Mode Toggle */}
+        <div className="flex items-center gap-1 rounded bg-editor-surface border border-editor-border p-1">
+          <button
+            onClick={() => setViewMode('all')}
+            className={`px-2 py-1 text-xs rounded transition-colors ${
+              viewMode === 'all'
+                ? 'bg-editor-accent text-white'
+                : 'text-editor-text-muted hover:text-editor-text'
+            }`}
+          >
+            All
+          </button>
+          <button
+            onClick={() => setViewMode('cut')}
+            className={`px-2 py-1 text-xs rounded transition-colors ${
+              viewMode === 'cut'
+                ? 'bg-red-500/30 text-red-500'
+                : 'text-editor-text-muted hover:text-editor-text'
+            }`}
+          >
+            Cut
+          </button>
+          <button
+            onClick={() => setViewMode('mute')}
+            className={`px-2 py-1 text-xs rounded transition-colors ${
+              viewMode === 'mute'
+                ? 'bg-orange-500/30 text-orange-500'
+                : 'text-editor-text-muted hover:text-editor-text'
+            }`}
+          >
+            Mute
+          </button>
+          <button
+            onClick={() => setViewMode('gain')}
+            className={`px-2 py-1 text-xs rounded transition-colors ${
+              viewMode === 'gain'
+                ? 'bg-amber-500/30 text-amber-500'
+                : 'text-editor-text-muted hover:text-editor-text'
+            }`}
+          >
+            Gain
+          </button>
+        </div>
+      </div>
+
+      {totalZones === 0 ? (
+        <div className="p-4 rounded border border-dashed border-editor-border text-center">
+          <p className="text-xs text-editor-text-muted">
+            No zones yet. Create zones from the toolbar or by highlighting words.
+          </p>
+        </div>
+      ) : (
+        <div className="space-y-3">
+          {/* Cut Zones */}
+          {(viewMode === 'all' || viewMode === 'cut') && cutRanges.length > 0 && (
+            <div className="space-y-2">
+              <div className="text-xs font-semibold text-red-500/80 flex items-center gap-2">
+                <Scissors className="w-3.5 h-3.5" />
+                Cut Zones ({cutRanges.length})
+              </div>
+              <div className="space-y-1">
+                {cutRanges.map((range) => (
+                  <div
+                    key={range.id}
+                    className={`px-2 py-1.5 rounded border text-xs flex items-center gap-2 group ${getZoneTypeColor('cut')}`}
+                  >
+                    <div className="flex-1 min-w-0">
+                      <div className="font-medium truncate">
+                        {range.start.toFixed(2)}s – {range.end.toFixed(2)}s
+                      </div>
+                      <div className="text-editor-text-muted text-[10px]">{range.id}</div>
+                    </div>
+                    <button
+                      onClick={() => removeCutRange(range.id)}
+                      className="p-1 rounded hover:bg-red-500/20 text-red-500/70 hover:text-red-500 opacity-0 group-hover:opacity-100 transition-opacity"
+                      title="Delete cut zone"
+                    >
+                      <Trash2 className="w-3.5 h-3.5" />
+                    </button>
+                  </div>
+                ))}
+              </div>
+            </div>
+          )}
+
+          {/* Mute Zones */}
+          {(viewMode === 'all' || viewMode === 'mute') && muteRanges.length > 0 && (
+            <div className="space-y-2">
+              <div className="text-xs font-semibold text-orange-500/80 flex items-center gap-2">
+                <Volume2 className="w-3.5 h-3.5" />
+                Mute Zones ({muteRanges.length})
+              </div>
+              <div className="space-y-1">
+                {muteRanges.map((range) => (
+                  <div
+                    key={range.id}
+                    className={`px-2 py-1.5 rounded border text-xs flex items-center gap-2 group ${getZoneTypeColor('mute')}`}
+                  >
+                    <div className="flex-1 min-w-0">
+                      <div className="font-medium truncate">
+                        {range.start.toFixed(2)}s – {range.end.toFixed(2)}s
+                      </div>
+                      <div className="text-editor-text-muted text-[10px]">{range.id}</div>
+                    </div>
+                    <button
+                      onClick={() => removeMuteRange(range.id)}
+                      className="p-1 rounded hover:bg-orange-500/20 text-orange-500/70 hover:text-orange-500 opacity-0 group-hover:opacity-100 transition-opacity"
+                      title="Delete mute zone"
+                    >
+                      <Trash2 className="w-3.5 h-3.5" />
+                    </button>
+                  </div>
+                ))}
+              </div>
+            </div>
+          )}
+
+          {/* Gain Zones */}
+          {(viewMode === 'all' || viewMode === 'gain') && gainRanges.length > 0 && (
+            <div className="space-y-2">
+              <div className="text-xs font-semibold text-amber-500/80 flex items-center gap-2">
+                <SlidersHorizontal className="w-3.5 h-3.5" />
+                Gain Zones ({gainRanges.length})
+              </div>
+              
+              {/* Global Gain Slider */}
+              <div className="px-2 py-2 rounded border border-amber-500/20 bg-amber-500/5 space-y-2">
+                <label className="text-xs text-editor-text-muted font-medium">Global Gain</label>
+                <div className="flex items-center gap-2">
+                  <input
+                    type="range"
+                    min={-24}
+                    max={24}
+                    step={0.5}
+                    value={globalGainDb}
+                    onChange={(e) => setGlobalGainDb(Number(e.target.value))}
+                    className="flex-1 h-1.5"
+                  />
+                  <input
+                    type="number"
+                    min={-24}
+                    max={24}
+                    step={0.5}
+                    value={globalGainDb}
+                    onChange={(e) => setGlobalGainDb(Math.max(-24, Math.min(24, Number(e.target.value) || 0)))}
+                    className="w-14 px-1.5 py-0.5 text-xs bg-editor-surface border border-editor-border rounded focus:border-editor-accent focus:outline-none"
+                  />
+                  <span className="text-xs text-amber-500/80 font-medium w-6 text-right">dB</span>
+                </div>
+              </div>
+              
+              <div className="space-y-1">
+                {gainRanges.map((range) => (
+                  <div
+                    key={range.id}
+                    className={`px-2 py-1.5 rounded border text-xs flex items-center gap-2 group ${getZoneTypeColor('gain')}`}
+                  >
+                    <div className="flex-1 min-w-0">
+                      <div className="font-medium truncate">
+                        {range.start.toFixed(2)}s – {range.end.toFixed(2)}s
+                      </div>
+                      <div className="text-editor-text-muted text-[10px]">
+                        {range.gainDb > 0 ? '+' : ''}{range.gainDb.toFixed(1)} dB
+                      </div>
+                    </div>
+                    <input
+                      type="number"
+                      min={-24}
+                      max={24}
+                      step={0.5}
+                      value={range.gainDb}
+                      onChange={(e) => updateGainRange(range.id, Number(e.target.value) || 0)}
+                      className="w-16 px-1.5 py-0.5 text-xs bg-editor-surface border border-editor-border rounded focus:border-editor-accent focus:outline-none"
+                      title="Gain dB"
+                    />
+                    <button
+                      onClick={() => removeGainRange(range.id)}
+                      className="p-1 rounded hover:bg-amber-500/20 text-amber-500/70 hover:text-amber-500 opacity-0 group-hover:opacity-100 transition-opacity"
+                      title="Delete gain zone"
+                    >
+                      <Trash2 className="w-3.5 h-3.5" />
+                    </button>
+                  </div>
+                ))}
+              </div>
+            </div>
+          )}
+        </div>
+      )}
+    </div>
+  );
+}
diff --git a/frontend/src/store/editorStore.test.ts b/frontend/src/store/editorStore.test.ts
new file mode 100644
index 0000000..c87aac1
--- /dev/null
+++ b/frontend/src/store/editorStore.test.ts
@@ -0,0 +1,32 @@
+import { beforeEach, describe, expect, test } from 'vitest';
+
+import { useEditorStore } from './editorStore';
+
+
+describe('editorStore basics', () => {
+  beforeEach(() => {
+    useEditorStore.getState().reset();
+  });
+
+  test('clamps global gain to valid bounds', () => {
+    const state = useEditorStore.getState();
+
+    state.setGlobalGainDb(100);
+    expect(useEditorStore.getState().globalGainDb).toBe(24);
+
+    state.setGlobalGainDb(-100);
+    expect(useEditorStore.getState().globalGainDb).toBe(-24);
+  });
+
+  test('adds gain range to store', () => {
+    const state = useEditorStore.getState();
+
+    state.addGainRange(1.2, 2.4, 3.5);
+
+    const ranges = useEditorStore.getState().gainRanges;
+    expect(ranges.length).toBe(1);
+    expect(ranges[0].start).toBe(1.2);
+    expect(ranges[0].end).toBe(2.4);
+    expect(ranges[0].gainDb).toBe(3.5);
+  });
+});
diff --git a/scripts/check-feature-spec.sh b/scripts/check-feature-spec.sh
new file mode 100755
index 0000000..15cb376
--- /dev/null
+++ b/scripts/check-feature-spec.sh
@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$ROOT_DIR"
+
+log() {
+  printf '[check-feature-spec] %s\n' "$1"
+}
+
+BASE_SHA="${BASE_SHA:-}"
+if [[ -z "$BASE_SHA" ]]; then
+  if git rev-parse --verify origin/main >/dev/null 2>&1; then
+    BASE_SHA="$(git merge-base origin/main HEAD)"
+  else
+    log "No BASE_SHA and origin/main unavailable; skipping check."
+    exit 0
+  fi
+fi
+
+if ! git rev-parse --verify "$BASE_SHA" >/dev/null 2>&1; then
+  log "BASE_SHA '$BASE_SHA' not found; skipping check."
+  exit 0
+fi
+
+changed_files="$(git diff --name-only "$BASE_SHA"...HEAD)"
+if [[ -z "$changed_files" ]]; then
+  log "No changed files; nothing to enforce."
+  exit 0
+fi
+
+code_changed=0
+spec_changed=0
+
+while IFS= read -r path; do
+  [[ -z "$path" ]] && continue
+
+  case "$path" in
+    frontend/src/*|backend/*|src-tauri/src/*|shared/project-schema.json)
+      code_changed=1
+      ;;
+  esac
+
+  case "$path" in
+    docs/specs/*.md)
+      spec_changed=1
+      ;;
+  esac
+done <<< "$changed_files"
+
+if [[ "$code_changed" -eq 0 ]]; then
+  log "No app code changes detected; spec file not required."
+  exit 0
+fi
+
+if [[ "$spec_changed" -eq 1 ]]; then
+  log "Spec requirement satisfied."
+  exit 0
+fi
+
+log "Code changes detected without spec update in docs/specs/."
+log "Add or update at least one spec file using docs/spec-template.md."
+exit 1