ci(standalone): run the crate's tests, and compile the platform-gated Rust

.github/workflows/ci.yml

@@ -87,6 +87,60 @@ jobs:
         run: npx tsc --noEmit
         working-directory: standalone
 
-      - name: Cargo check
-        run: cargo check
+      # `cargo test` rather than `cargo check`: the crate carries unit tests
+      # (path/session/sidecar resolution in lib.rs) that no job ran, so they
+      # compiled at most as `cargo check` and never executed. Building the test
+      # harness also links, which `check` does not.
+      - name: Cargo test
+        run: cargo test
+        working-directory: standalone/src-tauri
+
+  standalone-platform-check:
+    # The job above runs on Linux only, so it compiles none of the crate's
+    # `#[cfg(windows)]` / `#[cfg(target_os = "macos")]` code — two whole modules
+    # (clipboard_win.rs, pe_subsystem.rs), the platform arms throughout lib.rs
+    # and build.rs, and the unit tests gated with them. Without this job their
+    # first compile is the Windows / macOS leg of release.yml, which runs only on
+    # a `v*` tag: a typo in Windows-only Rust surfaces as a failed release rather
+    # than as a failed PR. Deliberately a separate job from the smoketest above,
+    # so that job keeps its registered check name.
+    name: Standalone Platform Check (${{ matrix.platform }})
+    strategy:
+      # Each platform's compile is independent; a Windows failure must not hide
+      # what macOS would have said.
+      fail-fast: false
+      matrix:
+        platform: [windows-latest, macos-latest]
+    runs-on: ${{ matrix.platform }}
+
+    # A hung compile on a premium-billed runner must not ride the 6-hour job
+    # default. Cold-cache runs land at ~2min (macOS) and ~5min (Windows).
+    timeout-minutes: 20
+
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      # Same pin-driven setup as the smoketest above: build.rs fails unless the
+      # Node.js on PATH matches package.json's devEngines.runtime.version.
+      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version-file: package.json
+
+      - uses: dtolnay/rust-toolchain@4360b52568e2003a75bf9bc1d59f33a8e3fc893c # stable
+
+      # Windows and macOS runners bill at a multiple of Linux, so the dependency
+      # compile is cached rather than paid on every PR.
+      - name: Rust cache
+        uses: swatinem/rust-cache@6323deb102c322ba6fcbdcafc7e3dddab59af2b6 # v2
+        with:
+          workspaces: standalone/src-tauri
+
+      # No pnpm install and no TypeScript check here. The TS check is
+      # platform-independent and the smoketest above already runs it; and the Rust
+      # build never reads node_modules — build.rs needs only `node` on PATH (it
+      # resolves the binary with `node -p process.execPath`) plus the root
+      # package.json version pin. This job exists for the Rust the smoketest
+      # cannot see.
+      - name: Cargo test
+        run: cargo test
         working-directory: standalone/src-tauri