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:

• Vendored core: submodule pins repointed at Layr-Labs/mlx / Layr-Labs/mlx-c and bumped through MLX 0.32.0/0.32.2; Package.swift exposing Cmlx as a public product and wiring the JACCL distributed backend; Xcode project + regeneration scripts.
• C headers mirrored from the pinned forks; regenerated JIT Metal sources (Source/Cmlx/mlx-generated/**, called out honestly as regenerated, not hand-written).
• Swift runtime surface: memory accounting + AllocationFootprint, process-global default streams (MLX 0.32 thread-local encoder fix), EvalProbe + eval-lock ordering, Gemma 4 expert-QMM diagnostics, quantized constant reuse (ConstantArrayCastCache), mutableInputs on custom Metal kernels, FFT/IO API drift.
• Tests; fork tooling. .github/** and fork.yaml are 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-swift/.

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, so a stale page is never published. FORKDIFF.md documents the day-to-day and the rebase procedure; the README links the page.

Base

Upstream main at 2026-06-17, e23ae6b2cf96737bbd31a34ed304123162f8c409 (= git merge-base origin/main upstream/main). Fork diff against it: 179 files (173 pre-existing + this PR's 6), all described.

One-time admin step

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

Verification

• python3 scripts/check_forkdiff.py --upstream-ref upstream/main → changed files 179 described 179, exit 0.
• go run github.com/protolambda/forkdiff@v0.1.1 renders 2.9 MB with every section present and nothing unmatched.
• This PR exercises the CI path itself: Fork Diff Check fetches upstream, runs the gate, renders the page as an artifact.
• The gate script and workflows are shared verbatim with the other Layr-Labs MLX forks (mlx, mlx-c, mlx-swift-lm) and with the harness repo, where the script has a pytest suite including an end-to-end rebase.

🤖 Generated with Claude Code