name: "Cache the Rust build"
description: >-
  Cache the Cargo registry and target directory the root package's build needs,
  so only the first job on a given Cargo.lock compiles the bridge from scratch.

  litellm builds through maturin, which compiles litellm-rust/crates/python-bridge
  in release mode before it can produce a wheel. `uv sync` therefore pays a full
  build in every job that installs the workspace: measured at 2m40s per unit shard
  on 2026-08-21, more than the whole unit tier spends running tests. Nothing caught
  it, because the uv cache holds wheels uv downloads rather than wheels it builds,
  and a path dependency whose source moves every commit could never hit that cache
  anyway. Cargo rebuilds only what changed when its target directory survives, so a
  warm job pays for the bridge crate alone.

  The key namespace is separate from test-rust.yml's. Both cache the same directory,
  but that workflow fills it with debug and clippy artifacts, which a release build
  cannot reuse, and a shared key would let whichever ran first deny the other a save.

runs:
  using: composite
  steps:
    - name: Restore the Cargo registry and target directory
      uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
      with:
        path: |
          ~/.cargo/registry
          ~/.cargo/git
          litellm-rust/target
        key: ${{ runner.os }}-cargo-release-${{ hashFiles('litellm-rust/Cargo.lock') }}
        restore-keys: |
          ${{ runner.os }}-cargo-release-