feat(forkdiff): fork-diff page on GitHub Pages + CI gate that a rebase must update it

[ethenotethan]

What

Fork-diff page (op-geth style, via protolambda/forkdiff). fork.yaml at the root names the upstream commit this fork sits on and groups every file the fork changes into a described section: the core pin to Layr-Labs/mlx; allocator observability and footprint policy (mlx_get_num_resources / mlx_get_resource_limit, mlx_get_memory_snapshot, mlx_get_allocation_footprint_policy + bound helpers); array buffer metadata and the constant-cache identity; mutable-input Metal kernels and the MLX 0.32.2 SDPA signature; cross-thread default streams; fork tooling. CI config is globally ignored. .github/workflows/forkdiff-pages.yml renders it on every push to main and deploys to GitHub Pages → https://layr-labs.github.io/mlx-c/.

One-time admin step. GitHub Pages must be enabled by a repo admin (Settings → Pages → Source: GitHub Actions); the workflow token cannot do that. Until then the deploy workflow still builds the page, keeps it as the forkdiff-page run artifact, and exits with a notice rather than failing.

Enforcement gate. scripts/check_forkdiff.py runs on every PR (forkdiff-check.yml) and fails when:

Drift	Check
rebase onto newer upstream	base.hash ≠ git merge-base HEAD upstream/main, or not an ancestor of upstream main
new fork change nobody described	a path in git diff base.hash..HEAD matches no section glob / global ignore
section describing code the fork no longer carries	a glob matches nothing

It also renders the page, so a fork.yaml forkdiff rejects can't merge; the deploy workflow runs the same check first. FORKDIFF.md documents the day-to-day (what to do when the gate lists files; how to bump base.hash after a rebase); the README links the page. The script is the same one used across the Layr-Labs MLX forks.

Base

Upstream main at 2026-04-23, fba4470b89073180056c9ea46c443051375f7399 ("regenerate bindings for MLX 0.31.2"). The fork diff against it is 10 files (+240/−3), all described; with this tooling, 16.

Verification

• python3 scripts/check_forkdiff.py --upstream-ref upstream/main → changed files 16 described 16, exit 0.
• Page rendered locally with go run github.com/protolambda/forkdiff@v0.1.1: all six sections present, nothing unmatched.
• This PR exercises the CI path itself: the Fork Diff Check job fetches upstream, runs the gate, and renders the page as an artifact.

🤖 Generated with Claude Code