feat: bundle platform-specific cmakefmt binaries (draft)

[puneetmatharu]

Summary

• Replace the single-platform publish workflow with a 6-target matrix that downloads the upstream cmakefmt binary per platform, embeds it into a platform-specific .vsix, and uploads the result as a workflow artifact.
• Teach src/extension.ts to prefer the bundled binary (bin/cmakefmt-<target>[.exe]) over PATH, with a clean three-step resolution: user override → bundled binary → PATH fallback.
• bin/ is gitignored (binaries never committed) but not excluded from .vscodeignore (so it is included in the .vsix).
• README updated with a TENTATIVE note that most users won't need a manual install.

This PR does not publish anything. The workflow only produces .vsix artifacts for local inspection. Publishing steps are intentionally omitted — see checklist below.

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VS Code target → Rust triple mapping

Verified against cmakefmt v1.4.0 (released 2026-05-02).
Asset URL pattern: https://github.com/cmakefmt/cmakefmt/releases/download/v{VERSION}/cmakefmt-{VERSION}-{TRIPLE}.{tar.gz|zip}

VS Code --target	Rust triple	Archive	Status
darwin-arm64	aarch64-apple-darwin	cmakefmt-{VERSION}-aarch64-apple-darwin.tar.gz	✅ available
darwin-x64	x86_64-apple-darwin	cmakefmt-{VERSION}-x86_64-apple-darwin.tar.gz	✅ available
linux-x64	x86_64-unknown-linux-gnu	cmakefmt-{VERSION}-x86_64-unknown-linux-gnu.tar.gz	✅ available
linux-arm64	aarch64-unknown-linux-gnu	cmakefmt-{VERSION}-aarch64-unknown-linux-gnu.tar.gz	✅ available
alpine-x64	x86_64-unknown-linux-musl	cmakefmt-{VERSION}-x86_64-unknown-linux-musl.tar.gz	✅ available
win32-x64	x86_64-pc-windows-msvc	cmakefmt-{VERSION}-x86_64-pc-windows-msvc.zip	✅ available
win32-arm64	aarch64-pc-windows-msvc	—	❌ blocked: needs upstream support
linux-armhf	armv7-unknown-linux-gnueabihf	—	❌ blocked: needs upstream support
alpine-arm64	aarch64-unknown-linux-musl	—	❌ blocked: needs upstream support

CMAKEFMT_VERSION is pinned as a workflow-level env var — bump it in one place when a new upstream release ships.

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Remaining work checklist

• Verify archive structure — confirm the exact binary path inside .tar.gz/.zip archives against actual v1.4.0 release assets. The find _extract -name cmakefmt approach in the workflow is robust but should be smoke-tested against the real download.
• macOS code signing / notarization — embedded binaries must be signed/notarized before macOS users can run them without a Gatekeeper prompt. This is the main blocker before shipping darwin-* targets.
• Windows Authenticode signing — similar requirement for win32-x64.
• Pin actions/upload-artifact to a commit SHA — currently using @v4 tag; pin for supply-chain safety, consistent with the rest of the repo.
• Alpine detection in extension.ts — process.platform returns "linux" on Alpine, so alpine users fall back to PATH even when alpine-x64 is bundled. Add musl/Alpine detection as a follow-up.
• Open VSX publishing — add an ovsx publish step once .vsix artifacts are inspected and signing is configured.
• Remove deprecated cmakefmt.onSave setting — already marked deprecated in package.json; drop it in a v2.0.0 breaking-change release.
• Bump extension to v2.0.0 — signal the new zero-config install model once platform bundles ship publicly.
• Upstream gaps — open or track issues in cmakefmt/cmakefmt for win32-arm64, linux-armhf, and alpine-arm64 Rust triples.

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Test plan

1. Trigger the workflow manually: Actions → Release → Run workflow, leave cmakefmt_version blank (uses pinned 1.4.0). Confirm all 6 matrix jobs complete and each produces a .vsix artifact.
2. Inspect a .vsix: unzip vscode-cmakefmt-linux-x64.vsix -d out/, confirm extension/bin/cmakefmt-linux-x64 exists and is executable (file + chmod check).
3. Install locally: code --install-extension vscode-cmakefmt-linux-x64.vsix, open a CMakeLists.txt, run Format Document — confirm formatting works without cmakefmt on PATH.
4. User override: set cmakefmt.executablePath to a custom binary path, confirm it takes precedence over the bundled binary.
5. PATH fallback: install the .vsix on a platform with no bundled binary (e.g. alpine-arm64), confirm it falls back to cmakefmt on PATH and shows a clear error if not found.
6. Non-platform CI build: confirm npm run package (the existing CI job) still produces a valid universal .vsix with an empty bin/ directory — no regressions.