ci(link): gate pull requests into main on fmt, clippy, and test

This repo had no pull_request workflow at all — release.yml runs only
after merge, so its `cargo fmt --check` gate was the first thing to see
new code, and an unformatted commit killed the release job before it
could build, tag, or publish (run for 2301c57).

Add pr-checks.yml, mirroring release.yml's gates in the same order so a
green PR implies the release clears its own gates:

  cargo fmt --check
  cargo clippy --locked --all-targets -- -D warnings
  cargo test --locked

One job, not three: bootstrapping the toolchain costs more than the
checks, so parallel jobs would pay it three times for no wall-clock win.
Cargo registry and target/ are cached on Cargo.lock. The crate is
already clean at `-D warnings`, so clippy starts green.

Co-Authored-By: Claude <noreply@anthropic.com>

.gitea/workflows/pr-checks.yml

@@ -0,0 +1,101 @@
+# Gate every pull request into `main` on the same Rust checks the release runs,
+# so a formatting slip, a lint regression, or a failing test can't reach the
+# deployable branch.
+#
+# Why this exists: release.yml runs only AFTER merge (on push to `main`) and its
+# FIRST Rust step is `cargo fmt --check`. Before this workflow, an unformatted
+# commit merged cleanly and then killed the release job before it could build,
+# tag, or publish anything — the repo had no pull_request workflow at all. These
+# gates are deliberately a mirror of release.yml's, in the same order, so a green
+# PR means the release will get past its gates too.
+#
+# Enforcement (one-time, in the Gitea UI):
+#   Repository Settings → Branches → Branch Protection (rule for `main`)
+#     • Enable Status Check
+#     • Status check patterns:  PR Checks / *
+#   Note: Gitea only lists a context in its dropdown after it has reported once,
+#   so let this workflow run on one PR first. The `PR Checks / *` glob matches
+#   without needing the dropdown.
+#
+# Scope note: this gates PRs into `main` only. Feature work that lands on an
+# integration branch first (e.g. `edge`) is still caught on the branch's PR into
+# `main`. To gate that earlier hop too, add the branch to the `branches:` list
+# below — nothing else needs to change.
+#
+# Runner: the same self-hosted `ubuntu-latest` runner release.yml uses. Rust is
+# not assumed to be preinstalled, so the toolchain step bootstraps it the same
+# way release.yml does (minus the MinGW cross-compile deps — PRs build for the
+# host only; the Windows cross-build stays a release-time concern).
+
+name: PR Checks
+
+on:
+  pull_request:
+    branches: [main]
+
+# A newer push to the same PR cancels the in-flight run.
+concurrency:
+  group: pr-checks-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  WORKDIR: sidecar
+
+jobs:
+  rust-gates:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v4
+
+      # One job runs all three gates on purpose: installing the toolchain costs
+      # far more than the checks themselves, so splitting fmt/clippy/test into
+      # parallel jobs would pay that cost three times for no wall-clock win.
+      - name: Install Rust toolchain (rustfmt + clippy)
+        run: |
+          set -euo pipefail
+          SUDO=""; [ "$(id -u)" -ne 0 ] && SUDO="sudo"
+          $SUDO apt-get update
+          $SUDO apt-get install -y --no-install-recommends \
+            build-essential curl ca-certificates git
+
+          if ! command -v cargo >/dev/null 2>&1; then
+            curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
+              | sh -s -- -y --profile minimal --default-toolchain stable
+          fi
+          echo "${HOME}/.cargo/bin" >> "$GITHUB_PATH"
+          export PATH="${HOME}/.cargo/bin:${PATH}"
+          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
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            sidecar/target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('sidecar/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      # Cheapest gate first — parses only, no compile, so a formatting slip
+      # fails in seconds instead of after a full build.
+      - name: cargo fmt --check
+        working-directory: sidecar
+        run: cargo fmt --check
+
+      # --all-targets covers tests and examples, not just the binary.
+      # -D warnings makes a lint a failure; the crate is clean at this bar today,
+      # so anything new here is a regression introduced by the PR.
+      - name: cargo clippy
+        working-directory: sidecar
+        run: cargo clippy --locked --all-targets -- -D warnings
+
+      # --locked matches release.yml: it also proves Cargo.lock is in sync with
+      # Cargo.toml, rather than letting the build silently update it.
+      - name: cargo test
+        working-directory: sidecar
+        run: cargo test --locked

README.md

@@ -25,6 +25,7 @@ network-facing component, which is what keeps the game unreachable from the inte
 | Path | What |
 |------|------|
 | `sidecar/` | The Rust sidecar crate — terminates the loopback link to the shard, exposes WS + REST to the website. See [`sidecar/README.md`](sidecar/README.md). |
+| `.gitea/workflows/pr-checks.yml` | Gates every PR into `main` on `cargo fmt --check`, `cargo clippy -D warnings`, and `cargo test`. |
 | `.gitea/workflows/release.yml` | Builds + releases the sidecar binary (Linux + Windows) on every merge to `main`. |
 
 ## Build & run
@@ -42,6 +43,17 @@ cargo run --release
 every merge to `main` (conventional-commit versioning). See [`sidecar/README.md`](sidecar/README.md)
 for configuration and the wire protocol.
 
+Before that, `.gitea/workflows/pr-checks.yml` runs the same gates on every pull request into `main` —
+`cargo fmt --check`, `cargo clippy --all-targets -- -D warnings`, then `cargo test --locked`. Run them
+locally before pushing and the PR will be green:
+
+```bash
+cd sidecar
+cargo fmt                                        # or --check to just report
+cargo clippy --locked --all-targets -- -D warnings
+cargo test --locked
+```
+
 ## Deployment & compatibility
 
 The plugin ([RunicGateway/servuo-plugins](https://gitea.whitlocktech.com/RunicGateway/servuo-plugins))