ci: run whole workspace single-threaded on Windows (skia/DirectWrite)

The STATUS_ACCESS_VIOLATION is not confined to op-host-native/-desktop: any
crate whose tests reach a skia FontMgr (DirectWrite) via NativeBackend or
SkiaMeasure crashes when that test binary runs across parallel worker threads
(op-host-services surfaced next). Excluding crates one-by-one doesn't
converge. Instead run the entire workspace with --test-threads=1 on Windows
only; each binary is serialized (cross-process concurrency is safe), covering
every skia-touching crate at once. macOS / Linux stay parallel.

.github/workflows/rust-check.yml

@@ -71,15 +71,21 @@ jobs:
       # EGL, so STEP1A_REQUIRE_GPU is left unset: the op-host-native GPU
       # smoke (memory_loop) self-uses the raster fallback instead of
       # hard-failing on EGL init. Real-GPU coverage runs on dev machines.
-      - run: cargo test --workspace --exclude op-host-native --exclude op-host-desktop
-      # op-host-native (+ op-host-desktop, which wraps it) build native
-      # `NativeBackend`s that create a skia `FontMgr` (DirectWrite on Windows).
-      # Concurrent DirectWrite init/use across cargo's parallel test-worker
-      # threads segfaults on the Windows runner (STATUS_ACCESS_VIOLATION), so
-      # serialize both crates' tests. macOS / Linux are unaffected either way.
-      - run: cargo test -p op-host-native -p op-host-desktop -- --test-threads=1
+      # Windows runs the whole workspace single-threaded. Many crates' tests
+      # (op-host-native / -desktop / -services / …) trigger a skia `FontMgr`
+      # (DirectWrite on Windows) via NativeBackend or SkiaMeasure; concurrent
+      # DirectWrite init across a test binary's parallel worker threads
+      # segfaults (STATUS_ACCESS_VIOLATION). `--test-threads=1` serializes each
+      # binary — cross-binary (separate-process) concurrency is safe, so one
+      # flag covers every skia-touching crate. macOS / Linux run in parallel.
+      - name: Test workspace (non-Windows, parallel)
+        if: runner.os != 'Windows'
+        run: cargo test --workspace
+      - name: Test workspace (Windows, serialized — skia/DirectWrite)
+        if: runner.os == 'Windows'
+        run: cargo test --workspace -- --test-threads=1
       - name: Run CanvasKit web host tests
-        run: cargo test -p op-host-web --features canvaskit
+        run: cargo test -p op-host-web --features canvaskit -- --test-threads=1
       - run: cargo clippy --workspace --all-targets -- -D warnings
       # Step 1a Phase C Task 4: spec v19 §11 + §12.3 boundary invariants.
       # Linux runner has the full mobile target stdlib (`rustup target add`

.github/workflows/rust-multiplatform.yml

@@ -114,19 +114,18 @@ jobs:
         # EGL/Mesa stack they soft-skip (INCONCLUSIVE eprintln); set
         # STEP1A_REQUIRE_GPU=1 on a known-good GPU runner to fail hard.
         run: cargo test --workspace --target ${{ matrix.target }}
-      - name: Test (host, macOS / Windows)
-        if: matrix.cross == false && matrix.check_only != true && runner.os != 'Linux'
-        run: cargo test --workspace --exclude op-host-native --exclude op-host-desktop --target ${{ matrix.target }}
-      - name: Test skia host crates (macOS / Windows, serialized)
-        if: matrix.cross == false && matrix.check_only != true && runner.os != 'Linux'
-        # op-host-native (+ op-host-desktop) build native NativeBackends whose
-        # skia FontMgr (DirectWrite) segfaults across parallel test-worker
-        # threads on the Windows runner (STATUS_ACCESS_VIOLATION). Run
-        # single-threaded (matches rust-check.yml). A SEPARATE step — not a
-        # second line in the step above — because Windows runs multi-line
-        # run: blocks under PowerShell, which only fails on the LAST command's
-        # exit code and would mask a failure in the workspace test above.
-        run: cargo test -p op-host-native -p op-host-desktop --target ${{ matrix.target }} -- --test-threads=1
+      - name: Test (host, macOS — parallel)
+        if: matrix.cross == false && matrix.check_only != true && runner.os == 'macOS'
+        run: cargo test --workspace --target ${{ matrix.target }}
+      # Windows runs the whole workspace single-threaded: many crates' tests
+      # trigger a skia FontMgr (DirectWrite) via NativeBackend / SkiaMeasure,
+      # and concurrent DirectWrite init across a test binary's parallel worker
+      # threads segfaults (STATUS_ACCESS_VIOLATION). --test-threads=1 serializes
+      # each binary; cross-binary (separate-process) concurrency is safe, so
+      # one flag covers every skia-touching crate. Matches rust-check.yml.
+      - name: Test (host, Windows — serialized skia/DirectWrite)
+        if: matrix.cross == false && matrix.check_only != true && runner.os == 'Windows'
+        run: cargo test --workspace --target ${{ matrix.target }} -- --test-threads=1
       # Desktop binary artifact upload is intentionally not wired here yet.
       # The real desktop binary lives in the `op-host-desktop` crate; a
       # build + upload step can be added once release packaging is finalized.