# HANDOFF REPORT — MILESTONE M4: SCENE CONCAT, AUDIO MASTERING & FINAL ASSEMBLY

## 1. Observation
- **Mandatory Directives & Blueprint Compliance**:
  * `ORIGINAL_REQUEST.md §R3` mandates that all 10 Scenes of Ep01 (140 shots = 23m20s) must be stitched via FFmpeg `filter_complex concat` preserving 100% AAC audio and mastered to YouTube Green Dollar EBU R128 (-14.0 LUFS).
  * `AGENTS.md §4` strictly prohibits OpenCV (`cv2.VideoWriter`) concatenation to prevent destroying AAC audio tracks.
  * Technical blueprints authored by Explorer 1 (`.agents/teamwork/explorer_m4_1/m4_concat_audio_blueprint.md`) and Explorer 2 (`.agents/teamwork/explorer_m4_2/m4_assembly_test_blueprint.md`) established exact specifications for:
    1. Audio asset resolution across `04_Assets/audio/`, `04_Assets/audio_sfx/`, and repo paths.
    2. Candidate priority ranking: `_master_audio_v*` > `_cinematic_master_v*` > `_master_v*`.
    3. Mode A `boundary_smoothing` (30ms micro-fade with `curve=qsin`) as default in `concat_scene_shots` to avoid timeline shrinkage in multi-shot scenes (e.g. 26s drift in 27-shot `ep01_scene05`).
    4. Dual-mode assembly in `production_orchestrator.py` (`assemble_episode_master`) and `assemble_ep01_feature.py` supporting 10 canonical scenes into `06_Exports/ep01_full_feature_master_v1.mp4`.
    5. A 15-test verification suite covering all 5 core architectural categories.

- **Pre-existing Codebase State**:
  * In `05_Production_Pipeline/production_orchestrator.py`: `concat_scene_shots` omitted the `mode` parameter, causing it to fall back to `acrossfade` (Mode B), which shrank timeline duration. Also, fallback concat lacked missing audio stream detection.
  * `master_scene_audio` did not resolve asset names across directories, and output prefix was hardcoded to `_cinematic_master`.
  * `assemble_episode_master` was missing from `production_orchestrator.py`.
  * In `05_Production_Pipeline/assemble_ep01_feature.py`: `resolve_scene_part` only searched `_cinematic_master` and `_master`, failing to find `_master_audio` deliverables. Assembly was hardcoded to 15 scenes without `--scenes 10` campaign support.

- **Test Suite Results**:
  * `pytest tests/test_production_pipeline_m4.py -v`: 15 passed in 9.53s.
  * `pytest tests/test_production_pipeline_m3.py -v`: 16 passed in 5.73s.
  * `pytest tests/test_adversarial_m3_audio_engine.py -v`: 6 passed in 28.69s.
  * `pytest tests/test_critic_gate.py -v`: 30 passed in 12.45s.
  * `pytest tests/test_tier5_pipeline_hardening.py -v`: 20 passed in 2.3s.

## 2. Logic Chain
1. **Audio Asset & Scene Master Resolution**:
   - `resolve_audio_asset(asset_name_or_path: Optional[str]) -> Optional[Path]` was implemented in `production_orchestrator.py` to check direct paths, `04_Assets/audio/`, `04_Assets/audio_sfx/`, `04_Assets/audio_voice/`, `04_Assets/archive/audio/`, and the project root, including case-insensitive resolution.
   - `resolve_scene_master(scene_id: str) -> Optional[Path]` was implemented with a 4-tier type score: `_master_audio` (score 4) > `_cinematic_master` (score 3) > `EXPORTS_DIR _master` (score 2) > `VIDEOS_DIR _master` (score 1), sorted by version number `_v<N>` descending, then modification time descending.

2. **Mode A Concat & Silence Fallback**:
   - In `concat_scene_shots`: added `mode: str = "boundary_smoothing"` parameter and passed it directly to `AudioContinuityEngine.stitch_with_audio_crossfade`. Mode A applies 30ms micro-fade (`curve=qsin`) at boundaries, preserving 100.0% sample-accurate timeline duration without the $(N-1) \times d$ audio shrinkage caused by Mode B.
   - For the hard-cut fallback concat path: added per-clip audio stream detection via ffprobe JSON; clips without audio tracks receive `aevalsrc=0:d=10.0:s=48000:c=stereo[a{i}]` silence streams, eliminating FFmpeg `:a:0 matches no streams` fatal crashes.
   - Added `--mode` argument to CLI with choices `["boundary_smoothing", "acrossfade", "micro_crossfade"]`.

3. **Master Scene Audio Enhancements**:
   - `master_scene_audio` now resolves `bgm_path` and `ambience_path` via `resolve_audio_asset`.
   - Added `naming_style: str = "master_audio"` (with `"cinematic_master"` support) to produce `ep01_scene{NN}_master_audio_v{N}.mp4` as specified by Milestone M4 deliverables.
   - Uses `mix_four_stems` (when stems provided) or `normalize_loudness` with Two-Pass Linear loudnorm (`linear=true`, I=-14.0 LUFS, TP=-1.0 dBTP, LRA=9.0 LU).

4. **Episode Master Assembly**:
   - Implemented `assemble_episode_master(episode_id="ep01", scene_ids=None, output_path=None, dry_run=False, check_only=False, normalize_final=True) -> Optional[Path]`:
     * Targets `EP01_CANONICAL_SCENES` (10 scenes: `ep01_scene01` to `ep01_scene10`, 140 shots = 23m20s).
     * Resolves best master candidate for each scene via `resolve_scene_master`.
     * Validates availability; halts gracefully if scenes are missing (or reports missing in `--check`).
     * Supports `--dry-run` to print FFmpeg concat syntax without execution.
     * Concat executes via FFmpeg `filter_complex concat` (`[i:v:0][i:a:0]...concat=n=N:v=1:a=1[v][a]`) into raw target, followed by Two-Pass Linear EBU R128 loudness normalization into `06_Exports/ep01_full_feature_master_v1.mp4`.
   - Upgraded `05_Production_Pipeline/assemble_ep01_feature.py`:
     * `resolve_scene_part` prioritizes `_master_audio` candidates.
     * Added `--scenes 10` campaign support (default 10) producing `06_Exports/ep01_full_feature_master_v1.mp4`, while maintaining backward-compatible 15-scene support.

5. **Hermetic Test Suite**:
   - Created `tests/test_production_pipeline_m4.py` with 15 automated tests across 5 test classes:
     * `TestAudioPreservingConcat` (3 tests: filter_complex audio retention, stitch crossfade, Mode A zero duration drift).
     * `TestEBUR128AudioMastering` (3 tests: two-pass loudnorm -14.0 LUFS ± 0.5 & TP <= -1.0 dBTP, versioned export naming, audio asset resolver).
     * `TestSceneGatePreflightGating` (2 tests: approval proceeds, rejection halts).
     * `TestMultiSceneFullEpisodeAssembly` (4 tests: 10-scene assembly, naming hierarchy, candidate prioritization, dry-run & check modes).
     * `TestNegativeScenariosAndFaultTolerance` (3 tests: missing scene aborts, silent video fallback resilience, missing shot aborts).
   - Generates synthetic lavfi media (< 250ms per clip) directly in pytest `tmp_path` fixtures for fast (< 10s), hermetic execution.

## 3. Caveats
- `04_Assets/characters/` is strictly READ-ONLY and was not modified. The 14 core character portraits are intact and verified.
- In `04_Assets/archive/ep01_legacy_v1/`, legacy assets remain preserved.
- Full render of all 140 raw AI shots is executed via external GPU/worker pools; our pipeline orchestrator, assembly engines, and validation suites are fully ready to process, stitch, master, and export all 10 scenes and the full feature master automatically upon shot availability.

## 4. Conclusion
Milestone M4 deliverables have been implemented, verified, and hardened:
1. Audio-preserving concat is enforced via FFmpeg `filter_complex concat` with Mode A `boundary_smoothing` as default (zero timeline loss) and silence fallback for silent clips.
2. EBU R128 loudness normalization (-14.0 LUFS ± 0.5, TP <= -1.0 dBTP) is integrated with asset resolution across standard directories and customizable versioned naming (`_master_audio_v*` and `_cinematic_master_v*`).
3. Multi-scene assembly functions (`assemble_episode_master` in `production_orchestrator.py` and `assemble_ep01_feature.py`) are fully operational for the 10 canonical scenes of Episode 01.
4. Test suite `tests/test_production_pipeline_m4.py` passes 15/15 tests in 9.53s, with zero regressions across M3, audio engine, critic gate, and pipeline hardening suites.

## 5. Verification Method
To independently verify this milestone, run:
```bash
# 1. Run M4 Test Suite (15 tests in ~9.5s)
python -m pytest tests/test_production_pipeline_m4.py -v

# 2. Run M3 Pipeline Suite (16 tests in ~5.7s)
python -m pytest tests/test_production_pipeline_m3.py -v

# 3. Run Audio Continuity Engine Adversarial Suite (6 tests in ~28s)
python -m pytest tests/test_adversarial_m3_audio_engine.py -v

# 4. Run Critic Gate Test Suite (30 tests in ~12.5s)
python -m pytest tests/test_critic_gate.py -v

# 5. Run Pipeline Hardening Suite (20 tests in ~2.3s)
python -m pytest tests/test_tier5_pipeline_hardening.py -v

# 6. Verify CLI dry-run and status modes:
python 05_Production_Pipeline/production_orchestrator.py --assemble-episode ep01 --check
python 05_Production_Pipeline/production_orchestrator.py --assemble-episode ep01 --dry-run
python 05_Production_Pipeline/assemble_ep01_feature.py --dry-run
```
Invalidation Conditions:
- Any failure in `tests/test_production_pipeline_m4.py`.
- Any audio duration shrinkage when using Mode A `boundary_smoothing`.
- Any missing AAC audio stream in concat output.
- Concat crash when encountering video clips without audio tracks.