refactor(P1): M1 dead code removal + M3 blender_render.py split

M1 — dead code removed:
- Delete blender-renderer/ and threejs-renderer/ source files
- Remove PIL/Pillow fallback block from step_processor.py
  (_generate_thumbnail_placeholder, _finalise_image JPG path)
- Remove stl_quality param from render_blender.py, render_still_task,
  render_turntable_task (was always "low"; hardcode deflection values)
- render_turntable_task now reads scene_linear/angular_deflection from
  system_settings (consistent with export_glb.py pipeline)

M3 — blender_render.py split from 263 → 68 lines:
- _blender_args.py: parse_args() — all 25 positional + named args
- _blender_scene_setup.py: setup_scene() — MODE A/B including USD import
- _blender_render_config.py: configure_and_render() — engine + output

Post-review fixes:
- _db_engine.dispose() after settings read in render_turntable_task
- _finalise_image() fmt param removed (always PNG; PIL never installed)
- _blender_import.py committed together with new submodules to satisfy
  import_usd_file dependency

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

review-report.md

@@ -1,36 +1,50 @@
-# Review Report: Pipeline Cleanup (M1 + M3)
-Date: 2026-03-11
+# Review Report: P1 Remaining Cleanup — M1 Dead Code + M3 blender_render.py Split
+Date: 2026-03-12
 
-## Result: ✅ Approved (2 low-severity unused imports fixed inline)
+## Result: ⚠️ Minor issues
 
 ---
 
 ## Problems Found
 
-### render-worker/scripts/blender_render.py:20 — Unused `import math`
-**Severity**: Low
-**Description**: `import math` is at the top of the entry-point but `math` is no longer referenced there — all math operations moved to submodules.
-**Fix**: Remove the import. Applied inline.
+### [_blender_scene_setup.py:12] `import_usd_file` depends on uncommitted `_blender_import.py` change
+**Severity**: Medium
+**Description**: `_blender_scene_setup.py` imports `import_usd_file` from `_blender_import` (line 12). This function does NOT exist in the committed `_blender_import.py` at HEAD — it is only present in a pre-existing uncommitted modification to that file (`_blender_import.py` shows `??` is untracked/modified). If the new submodule files (`_blender_args.py`, `_blender_scene_setup.py`, `_blender_render_config.py`) are committed without including the `_blender_import.py` change, every Blender render will crash with `ImportError: cannot import name 'import_usd_file'`.
+**Recommendation**: Ensure `render-worker/scripts/_blender_import.py` (with the `import_usd_file` addition) is staged and committed in the same commit as the new submodule files.
 
-### render-worker/scripts/_blender_import.py:5 — Unused `import re as _re`
+---
+
+### [step_processor.py:561] `_finalise_image()` ignores `fmt` parameter — always produces `.png`
 **Severity**: Low
-**Description**: `re` module is imported at module level but not used anywhere in `_blender_import.py`. The `_re.sub` calls live in `_blender_materials.py`.
-**Fix**: Remove the import. Applied inline.
+**Description**: The new `_finalise_image(src, dst, fmt)` accepts `fmt` but always does `out = dst.with_suffix(".png")`. When `thumbnail_format = "jpg"` is configured in system settings, the callers compute `final_path` with a `.jpg` extension and pass `fmt="jpg"`, but the returned path will always have `.png` extension. The `fmt` parameter is silently ignored.
+
+This is a deliberate consequence of removing PIL (which was never installed anyway), so the behavior change is acceptable. However, the dead `fmt` parameter creates misleading API.
+**Recommendation**: Remove the `fmt` parameter from `_finalise_image()` and update all callers to drop it. This makes the intent clear: format conversion is not supported.
+
+---
+
+### [domains/rendering/tasks.py:210–215] New SQLAlchemy engine created per `render_turntable_task` call
+**Severity**: Low
+**Description**: `render_turntable_task` now calls `_create_engine(app_settings.database_url_sync)` inside the task body. This creates a new connection pool on every invocation. For a low-frequency task this is acceptable, but it leaks connection pool resources if the task runs frequently.
+**Recommendation**: The `_db_engine` should be disposed after use. Add `_db_engine.dispose()` after the `with _Session(_db_engine) as _s:` block closes.
 
 ---
 
 ## Positives
 
-- **Dead code thoroughly removed**: `VALID_STL_QUALITIES`, `stl_quality` (7 locations in admin.py), 6 frontend files, `_mark_sharp_and_seams()` (62 lines), `_render_via_service()` (33 lines), 2 dead `elif renderer == "threejs"` branches — all gone. All acceptance gates pass.
-- **Submodule decomposition is clean**: `blender_render.py` went 858 → 249 lines. Each submodule has a clear single responsibility with correct `sys.path.insert(0, ...)` for Blender Python discovery.
-- **GPU activation order preserved**: `activate_gpu()` still called before `open_mainfile`, and again after engine init — the critical 3-call sequence is intact in `configure_engine()`.
-- **FailedMaterial sentinel preserved**: `assign_failed_material` in `_blender_materials.py` matches the original logic; unmatched parts in `apply_material_library` are now handled internally.
-- **`part_names_ordered` global → parameter**: Correctly converted to an explicit parameter in `apply_material_library()`.
-- **No security issues**: No hardcoded credentials, no SQL injections, no new endpoints, no new models.
-- **No render pipeline regressions**: No references to removed blender-renderer or threejs-renderer services.
-- **Frontend**: TypeScript errors in output are pre-existing (Admin.tsx GPUProbeResult, InlineCadViewer.tsx), not introduced by this change.
+- **All 7 plan tasks complete**: blender_render.py correctly reduced from 263 → 68 lines (meets ≤ 80 target).
+- **`stl_quality` fully removed**: Zero matches in `render_blender.py`, `step_processor.py`, `domains/rendering/tasks.py` — clean sweep.
+- **PIL fallback completely excised**: `_generate_thumbnail_placeholder()` and `from PIL import Image` both gone; the 68-line Pillow-placeholder function is deleted, reducing `step_processor.py` by ~70 lines.
+- **Submodule separation is clean**: `_blender_args.py`, `_blender_scene_setup.py`, `_blender_render_config.py` follow the existing `_blender_gpu.py` / `_blender_import.py` / `_blender_scene.py` naming and import pattern exactly.
+- **`_blender_args.py` fidelity**: All 25 positional args correctly mapped; named args `--mesh-attributes` and `--usd-path` preserved; `use_template` bool computed and included in namespace; template file existence check preserved.
+- **`_blender_scene_setup.py` correctness**: MODE A and MODE B correctly separated; shadow catcher, lighting_only, auto-camera, and material library logic all preserved faithfully; `needs_auto_camera` conditional for MODE B correctly omits `setup_auto_lights` (template provides its own lights).
+- **`_blender_render_config.py` correctness**: `configure_engine` signature matches exactly; colour management block (`Standard`/`None` look) correctly gated on `not use_template`; CYCLES verification block preserved.
+- **`_lap` closure works correctly**: `_lap` is defined in `blender_render.py`, captures `_t0` and `_timings` from outer scope, passed as callback to both submodules — timing summary at end of `blender_render.py` correctly reflects labels from all phases.
+- **`render_turntable_task` GLB path fixed**: Changed from `f"{stem}_{stl_quality}.glb"` (always `_low.glb`) to `{stem}_thumbnail.glb` — now consistent with `render_blender.py` service cache key.
+- **Security**: No hardcoded credentials, no SQL injection vectors. Raw SQL in `render_turntable_task` is a parameterless `SELECT` with no user input.
 
 ---
 
 ## Recommendation
-Approved. Two unused imports fixed inline before commit.
+
+Fix the `_db_engine.dispose()` omission (low, 1 line) and commit `_blender_import.py` together with the new submodule files. The `fmt` parameter cleanup is optional polish. Fix inline and re-apply without re-review.