[umiyosh]

Closes #5. Part of #2. Stacked on #8 (base feat/quality-gates-ci); retarget to master after #8 merges.

Why

The CLI had no tests. This adds unit tests for the logic that decides what a video sounds and looks like, a render smoke test in headless Chromium, and kotobae's 80% coverage gate, all run in CI without a GEMINI_API_KEY.

What changed

• Vitest 3.2.7 with @vitest/coverage-v8, vitest.config.ts with 80% thresholds (lines, branches, functions, statements). make test, make test-coverage, and make check now includes the coverage gate.
• Small refactor so the logic is testable, no behavior change:
  • prepare moved from cli.ts to store.ts and throws instead of exiting.
  • placeOnFilm (narration placement on the film timeline) moved to work.ts and reports long narration through a callback.
  • The MP4 encode arguments moved to encodeArgs in audio.ts.
  • cli.ts is left as command wiring and is excluded from coverage; the smoke test runs it as a real process.
• Unit tests (48 in total):
  • script.json validation: defaults and every rejection message.
  • Scene timing: lengths from narration, speed, lead, tail and the final hold; timing.json parsing.
  • Narration placement on the film's actual scene starts, the overrun warning, unknown scene ids.
  • Gemini / Lyria requests with fetch mocked: URL, API key header, voice, the BGM prompt length, raw PCM to WAV, skipping unchanged scenes, three retries with the API's error message, missing key.
  • ffmpeg argument building with spawn mocked: narration delays, tempo, BGM loop, volume and fades in the filter graph, and the encode arguments.
  • prepare from a fixture store.
• Render smoke tests against tests/fixtures/player, a small stand-in for the Motion player with the same window.__animation hook. The real player is Anthropic's Motion code and is not committed. The tests check:
  • the scene layout and that frames differ between scenes;
  • that the film cannot reach the network (the stub tries fetch("https://example.com/") and must see it blocked);
  • the load-error path;
  • motion-render prepare + stills as a subprocess.
• CI:
  • installs Chromium with system dependencies;
  • lifts Ubuntu 24.04's AppArmor restriction on unprivileged user namespaces, because motion-render keeps Chromium's own sandbox on;
  • runs make test-coverage.
• README (EN / JA) Development and Layout sections and SKILL.md's file list are updated.

Verification

• make check locally: lint, format, typecheck, 48 tests pass, coverage lines 91.45% / branches 91.8% / functions 97.43% / statements 91.45%, quality gate tests, baseline unchanged
• CI passes on this pull request, including Chromium with its own sandbox on the Ubuntu runner

Not verified

• The tests run against the stub player, not the real Motion player. A full /motion-render:motion-render run with the real player is tracked in Migrate the CLI scripts to TypeScript #3.