chore: build hygiene — MSRV job, cache scoping, dep dedup

.github/workflows/ci.yml

@@ -59,6 +59,34 @@ jobs:
       - name: Run Rust tests
         run: cargo test --workspace
 
+  msrv:
+    name: MSRV (rust-version) check
+    runs-on: ubuntu-latest
+    env:
+      # rust-toolchain.toml pins stable for contributors; override here
+      # so the MSRV job actually exercises the declared minimum. Keep
+      # this in sync with `rust-version` in the workspace Cargo.toml.
+      RUSTUP_TOOLCHAIN: "1.88"
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Install MSRV toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.88"
+
+      - uses: Swatinem/rust-cache@v2.9.1
+        with:
+          prefix-key: v0-rust-msrv
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+
+      - name: Compile-check workspace on MSRV
+        # `--locked` keeps the MSRV deterministic: versions resolve from
+        # the committed Cargo.lock rather than the latest compatible
+        # crates.io release, so the declared MSRV stays honest until a
+        # deliberate `cargo update` changes the lockfile.
+        run: cargo check --workspace --locked
+
   test:
     needs: lint
     strategy:
@@ -79,6 +107,13 @@ jobs:
         uses: dtolnay/rust-toolchain@stable
 
       - uses: Swatinem/rust-cache@v2.9.1
+        with:
+          # Share one Rust cache across the two Python versions —
+          # pyo3 / abi3 builds don't vary by Python minor version.
+          shared-key: maturin-${{ matrix.os }}
+          # Keep the total-cache quota under control: only the main
+          # branch writes new cache entries; PRs read-only.
+          save-if: ${{ github.ref == 'refs/heads/main' }}
 
       - uses: astral-sh/setup-uv@v7
         with:

.gitignore

@@ -1,6 +1,5 @@
 # Rust
 target/
-Cargo.lock
 
 # Python
 __pycache__/