Fail closed when Manim timing helpers see corrupt timing.json

[jmjava]

Problem

Library load_bundle_timing now rejects non-object stems and non-array words / segments. Compiled scenes.py still used data.get(segment_key, {}).get("segments", []), so a list stem raised AttributeError at Manim construct(). scene-compile did not refresh those helpers.

Change

Bootstrap _load_timing / _load_timing_words raise TypeError on corrupt stem / inner types. Missing file or missing stem still returns [].

refresh_bootstrap_helpers and helper_api_violations treat the old bodies as stale so docgen scene-compile upgrades consumer scenes.py.

Tests

Local: ruff check src/ tests/ green; pytest tests/ 750 passed, 1 skipped; docgen benchmark meets src/docgen/benchmark_data/baseline.json (helper change, no --update-baseline).

• Executed helpers reject list stems and non-array inner fields
• Helpers still return object rows and [] for a missing stem
• Refresh rewrites stale loaders
• Scene-asset validate flags stale loaders

Out of scope

• Requiring numeric start / end on every word row