Greptile Summary

This PR consolidates the Rust compilation cache across all CI jobs from ~6 distinct keys (~10.8 GB) down to 3 shared keys (debug-ubuntu-latest, debug-macos-latest, msrv), reducing cache storage and improving cache hit rates for jobs like autofix and release-plz that previously had to compile from scratch.

• ci-other is designated as the sole cache writer (on main merges only), seeding a complete cache with test + clippy artifacts that all other jobs can reuse.
• build, autofix, and release-plz are read-only consumers (save-if: false), preventing cache churn.
• msrv retains a separate key since it uses a different Rust toolchain.
• On a cold-cache run (first run or after expiry), build and ci-other both compile independently since build never saves — this double compilation is an accepted trade-off for keeping the cache authoritative.
• No functional code changes; impact is purely on CI performance and cache storage.

Confidence Score: 5/5

• This PR is safe to merge — it only touches CI workflow cache configuration with no functional code changes.
• All three cache keys are logically correct, the read-only vs. read-write split aligns perfectly with the stated strategy, and there are no competing writes to the same key from concurrent jobs. The only trade-off (double compilation on cold cache) is intentional and documented.
• No files require special attention.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    MAIN[Main Branch Push] --> BUILD_U[build - ubuntu-latest\nsave-if: false]
    MAIN --> BUILD_M[build - macos-latest\nsave-if: false]
    MAIN --> CIO_U[ci-other - ubuntu-latest\nsave-if: true on main]
    MAIN --> CIO_M[ci-other - macos-latest\nsave-if: true on main]
    MAIN --> MSRV[msrv\nsave-if: true on main]
    MAIN --> RP[release-plz\nsave-if: false]

    PR[PR Trigger] --> AUTOFIX[autofix\nsave-if: false]

    subgraph CACHE["GitHub Actions Cache"]
        C1["debug-ubuntu-latest"]
        C2["debug-macos-latest"]
        C3["msrv"]
    end

    BUILD_U -- reads --> C1
    BUILD_M -- reads --> C2
    CIO_U -- reads + writes --> C1
    CIO_M -- reads + writes --> C2
    MSRV -- reads + writes --> C3
    RP -- reads --> C1
    AUTOFIX -- reads --> C1

_{Last reviewed commit: cf43c58}