The dev shell tracked `stable.latest` and CI used `@stable`, so nothing
pinned a version and nothing declared a floor. A consumer on an older
toolchain hit a confusing error deep in a dependency rather than cargo
saying the version was too old, and a new stable release could turn a
lint into an unrelated red build.
- `rust-version = "1.88"` in Cargo.toml. The floor comes from the
dependency graph, not this crate's code: reqwest pulls in url -> idna
-> idna_adapter -> icu_*, and the icu crates require 1.88. Verified by
running the full suite against 1.88, not inferred.
- flake.nix pins the dev toolchain to 1.99.1 and adds an `msrv` devShell,
so the floor can be rechecked with
`nix develop .#msrv --command cargo test`.
- CI pins the main job to the same 1.99.1 and adds a job building on
1.88. Lint and format stay on the pinned toolchain only, since their
output varies by release.
Note the tradeoff: with CI pinned, a future stable that breaks the build
will not be noticed until the pin moves. Worth adding a non-blocking
`stable` job if that matters.
CLAUDE.md records the three places that must agree when either version
moves, and how to recheck the floor after a dependency bump.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
awkawbandClaude Opus 5
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