Pin LAME downloads to SHA-256, with a reviewed pin list that follows upstream

[soficis]

What changed

The MP3 fallback downloads a LAME encoder and runs it. Until now the only check was that lame --version printed something.

Pinning (a07d5dd)

• Every built-in source carries the SHA-256 of the exact archive. A mismatch deletes the download before anything is extracted or run; a source with no hash is refused.
• Homebrew bottles are fetched directly by pinned digest, replacing two manifest lookups through a mutable tag.
• The cached encoder is used only when a marker written by a verified install still matches it, so encoders cached before this change are downloaded again once.
• AUTOMIX_LAME_DOWNLOAD_URL and AUTOMIX_LAME_VERSION now require AUTOMIX_LAME_DOWNLOAD_SHA256.
• Windows on ARM uses the x64 build; its previous URL returns 404.

Pins that follow upstream

• assets/lame-pins.json is the current pin list. The app reads it from master before downloading and tries those sources first. The built-in pins stay as the fallback.
• The list can only name files under the known rarewares.org and Debian paths, or a Homebrew bottle digest. One bad entry rejects the whole list.
• tools/update_lame_pins.py regenerates the list; .github/workflows/lame_pins.yml runs it weekly and opens a pull request when pins change. Nothing is merged automatically.
• AUTOMIX_LAME_SKIP_PIN_UPDATE=1 keeps the app on the built-in pins.

Reviewer notes

• Stacked on Tensor inference, opt-in vocal separation, GPU runtime, and cross-platform CI #9. master does not compile with native ONNX enabled until Tensor inference, opt-in vocal separation, GPU runtime, and cross-platform CI #9 lands, so this branch is based on feat/tensor-inference.
• The repo becomes a runtime trust root for the encoder. Whoever can merge to master can change which file is accepted, within the allowed hosts. That is why the workflow opens a pull request instead of committing.
• Windows pins have no independent source. rarewares.org publishes no hashes; the two pins are the files as served on 2026-10-05, and the updater can only re-hash the same URLs. A new Windows build needs a manual URL change.
• The published list already differs from the built-in pins: Debian stable is at 3.100-6+b3 and Homebrew at LAME 4.0, whose macOS bottles start at macOS 14. Older Macs fall back to the built-in 3.100 bottles when the 4.0 one fails its --version check.
• Not exercised: a real end-to-end download in the app, the workflow itself (it needs "Allow GitHub Actions to create pull requests" enabled in repo settings), and the fetch of the list from master, which 404s until this is merged there.

Tests

ctest -C Release: 100% passed out of 267; the two known tensor-probe tests skip. Four new tests cover pin validity, the checked-in list, rejection of redirecting lists, and mismatch handling. Repo and workflow hygiene checks pass.

🤖 Generated with Claude Code