[schickling-assistant]

Problem

Cold Nix builds of ghostty-a887df4-zig-deps fail when GitHub archive endpoints return HTTP 5xx, blocking consumers before Rust compilation. The pinned imgui and zigimg archives are also available through codeload.

Goal

Make archive transport resilient without changing dependency contents or the package-cache output hash.

Decisions

• Derive GitHub archive records and byte checksums from the pinned Ghostty source's existing flatpak/zig-packages.json.
• Fetch each archive as its own fixed-output fetchurl derivation with urls = [ original codeload ].
• Replace those URL entries with immutable local archive paths in build.zig.zon.txt. Keep Ghostty's existing cache population script and all other fetching unchanged.
• Preserve ghosttyContract.zigDepsHash. Both archive checksums and the complete cache recursive output hash stay enforced.

Verification

PROOF PENDING: the local heavy-gate request is queued at this exact head. The proof will rebuild the two archive derivations with github.com forced to loopback, requiring codeload fallback, then --rebuild the complete cache against its unchanged recursive output hash. No existing store path is deleted. Results will be posted as a PR comment after completion; no successful local evaluation/build is claimed yet.

Complexity

Two archive inputs derived from upstream metadata, no new independent pin list or changed version. Reading the upstream manifest realizes its already-pinned source during evaluation.

Concerns

Archive transport only: Git sources and other archive origins retain their existing behavior. The FOD output is unchanged, so consumers that already have it need no fetch.

Release note

Improves cold-cache Nix build reliability during GitHub archive outages. No runtime behavior, API, schema, migration, or dependency content changes. README documents the fetch behavior.

Friction & bottlenecks

The archive outage prevents cold builds; local proof admission is queued behind shared build capacity.

Follow-ups

Consumer pin adoption after producer review and merge.

References

Content authority remains libghostty-vt-contract.json; archive metadata comes from the exact Ghostty revision it pins.

Posted on behalf of @schickling

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worktree	zig-archive-fallback/2026-11-08-zig-archive-fallback