Add CI gate for pull requests

.github/workflows/ci.yml

@@ -0,0 +1,35 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+# A newer push to the same PR cancels the run for the older commit.
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  # Job names `test (ubuntu-latest)` and `test (macos-latest)` are the
+  # required status checks in the `main` ruleset; keep them in sync.
+  test:
+    name: test (${{ matrix.os }})
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+      - uses: Swatinem/rust-cache@v2
+      - name: Format
+        run: cargo fmt --all --check
+      - name: Clippy
+        run: cargo clippy --workspace --all-targets -- -D warnings
+      - name: Test
+        run: cargo test --workspace

README.md

@@ -8,8 +8,12 @@ Custom [herdr](https://herdr.dev) plugins, built and linked from one repo.
 just          # build every plugin and link it with herdr
 just test     # run all tests
 just dev-one command-palette   # build + link one plugin
+just ci       # fmt + clippy + tests, same as the PR gate
 ```
 
+Pull requests into `main` must pass CI (`.github/workflows/ci.yml`: fmt,
+clippy with warnings denied, and tests on Linux and macOS) before merging.
+
 herdr launches plugin commands fresh each time, so after `just` the next
 invocation uses the new build. Relinking is safe; it refreshes the manifest.
 

justfile

@@ -15,3 +15,9 @@ dev-one name: (build name) (link name)
 # Run every test in the cargo workspace.
 test:
     cargo test --workspace
+
+# Run the same checks as the CI gate on pull requests.
+ci:
+    cargo fmt --all --check
+    cargo clippy --workspace --all-targets -- -D warnings
+    cargo test --workspace