Merge pull request 'ci(pr-checks): cache cargo with rust-cache so the cache stops growing' (#44) from chore/ci-self-cleanup into main

Reviewed-on: #44
Reviewed-by: Colby Whitlock <whitlocktech@gmail.com>

.gitea/workflows/pr-checks.yml

@@ -89,19 +89,16 @@ jobs:
           rustup component add rustfmt clippy
           cargo --version && cargo fmt --version && cargo clippy --version
 
-      # Keyed on Cargo.lock: dependency builds are reused until a dep actually
-      # changes. A cache miss only makes the run slower, never wrong.
-      - name: Cache cargo registry and build dir
+      # Dependency builds are reused until a dep actually changes; a cache miss
+      # only makes the run slower, never wrong. rust-cache rather than a plain
+      # actions/cache of target/: it strips this crate's own artifacts and
+      # anything stale before saving, and saves only on a miss. The plain cache
+      # restored the previous target/ and re-saved all of it under every new
+      # Cargo.lock, so each entry carried every older build and the runner's
+      # cache grew without bound.
+      - name: Cache cargo registry and dependency builds
         if: ${{ steps.detect.outputs.crate == 'true' }}
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            target
-          key: ${{ runner.os }}-cargo-${{ hashFiles('Cargo.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-cargo-
+        uses: Swatinem/rust-cache@v2
 
       # Cheapest gate first — parses only, no compile, so a formatting slip
       # fails in seconds instead of after a full build.