[kvlonge]

Why

Release wheel builds are slow and fragile on macOS. A cold arm64 dist build took 60 minutes in the 0.212.0 release, half of the 120-minute job limit, and a transient DNS error during the arm64 artifact upload cost a whole rebuild.

Changes

• The macOS wheel jobs restore compiled dependencies for dist builds through Swatinem/rust-cache, keyed on Cargo.lock, the toolchain, the cargo profile and the target.
• A new Dist Dependency Cache workflow is the only writer. It runs on pushes to main and daily, looks up both macOS keys and, when one is missing, builds only the macOS legs through Build Distributions and saves the dependencies. It has its own concurrency group, so its hour-long cold build does not hold back the Verify caches. Pull request, merge queue, Release Distributions and Publish runs can only restore.
• A failed wheel artifact upload retries once, replacing any partial artifact.
• The wheel job timeout rises from 120 to 150 minutes.

DuckShop edge case: not applicable. This is CI configuration only.

Verification

• actionlint passes on the changed workflows.
• A dispatch on a WIP branch built only the two macOS legs and skipped sdist. The writer lookup and the wheel-job restore computed identical keys, and save-if was false off main.
• The saving is measured after the first warm release build and reported then.
• One independent review, then a follow-up on its two fixed findings.