[kevinjqliu]

Which issue does this PR close?

• N/A (CI maintenance).

What changes are included in this PR?

rust-cache hashes every installed toolchain into its cache key, including the runner's preinstalled stable. We build with the nightly in rust-toolchain.toml and never use stable. But runner images roll out with different stable versions (1.99.0 vs 1.99.1 this week, on Linux, macOS and Windows), so each job ends up with 2 cache keys that can't restore from each other.

What that looks like over ~45 recent runs per workflow:

• The less common image misses a lot more. macOS build missed 4/4, Windows bindings 7/10, check-public-api 64% vs 37%.
• A miss rebuilds every dependency. For check-public-api that's ~6 min vs ~1 min.
• The duplicate entries take ~2.8GB. We're at 10.7GB of the 10GB cache limit, so they push out caches we still need.

Remove stable in setup-builder when it uses rust-toolchain.toml. Jobs that pass rust-version (audit, MSRV, publish, Python release) are unchanged. rust-toolchain.toml is still part of the key, so a nightly bump still invalidates the cache.

Apache Iggy does the same in its setup action.

Are these changes tested?

CI only. actionlint and zizmor --offline show no new findings. Checked locally that rustup toolchain uninstall stable exits 0 when stable is the default toolchain and when it's not installed. The hit rate only shows after this lands on main and the caches are re-saved.

AI Disclosure

Prepared with Copilot, including pulling the cache hit/miss numbers from run logs. Worth a look: that nothing in these jobs calls cargo +stable or relies on stable being installed.

[kevinjqliu]

this should improve cache hits and make ci faster

[kevinjqliu]

rejected by merge queue due to teh asf-allowlist-check, gh-action-pypi-publish needed a new version (fixed by #3531)

[Copilot]

Warning

Copilot couldn't run its full agentic review because it didn't start before the timeout. Make sure your repository has a runner available, or add a copilot-code-review.yml file specifying one with the runs-on attribute. See the docs for more details.

Copilot review overview

1 open issue

• rustup toolchain uninstall stable can make the job less reliable if stable is the current… · New

What changed in this PR

Updates the composite CI action to improve rust-cache hit rates by avoiding cache key divergence caused by runner-preinstalled stable toolchain versions.

Changes:

• Uninstalls the stable toolchain when using rust-toolchain.toml so caches are keyed only by the toolchain the repo actually uses.
• Adds inline rationale explaining why stable is removed (runner image variance and cache key splitting).

File	Description
.github/​actions/​setup-builder/​action.yml	Removes stable toolchain to keep rust-cache keys consistent across runner images.

_{Review effort: Lite}