fix(flake): switch to useFetchCargoVendor for crates.io UA compatibility#22
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crates.io added a User-Agent blocklist in late April 2026 that rejects requests without an identifying UA. nixpkgs has two crate-fetching paths: - fetchCargoVendor — patched in NixOS/nixpkgs#512735 (merged 2026-04-26) to send 'User-Agent: nixpkgs fetchCargoVendor/2' and fetch from static.crates.io - importCargoLock — used by cargoLock.lockFile = ...; has its own inline fetchCrate calling fetchurl; NOT yet patched upstream; receives 403 on every crate download Switching to useFetchCargoVendor + cargoHash routes through the patched path. Cargo.lock stays as the source of truth; only the flake.nix attribute changes.
ericbmerritt
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Summary
CI broke because crates.io added a User-Agent blocklist in late April 2026 and tightened it further in late May. nixpkgs has two crate-fetching paths; only one was patched upstream.
Root cause
fetchCargoVendor(Python-based)User-Agent: nixpkgs fetchCargoVendor/2 (https://github.com/NixOS/nixpkgs)and fetches fromstatic.crates.ioimportCargoLock(used bycargoLock.lockFile = ...)fetchCratecallingfetchurlwhich still hits the API endpoint without a UA → HTTP 403Our flake used
cargoLock.lockFile = self + "/Cargo.lock"— the broken path. Everynix buildfailed with:Fix
Switch the build path:
Cargo.lockstays in the repo as the source of truth;fetchCargoVendorreads it via the vendor step.Verified locally
nix build .#default— succeedsnix develop --command validate-wrap just validate— passes (the exact command CI runs)Follow-up
This unblocks every PR in the repo. PR #20 (spec) and PR #21 (ladder) need to rebase onto this once merged; they'll then pass CI cleanly. Worth filing an upstream nixpkgs issue against
importCargoLocksince no fix is in flight there yet — separate from this PR.