Fix Android CI and flaky GATT notification test

.github/workflows/swift.yml

@@ -57,33 +57,38 @@ jobs:
             run-tests: true
             build-tests: true
             free-disk-space: true
-            swift-test-flags: --no-parallel
+            # No --no-parallel here: the flags are passed verbatim to the on-device
+            # test runner binaries, and the XCTest runner rejects that option.
+            # Serial-execution races are instead fixed at the source by polling in
+            # the affected tests.
 
-  # Cross-compile the package and its tests for 64-bit ARM (aarch64) with the
-  # official Swift 6.3.2 Android SDK. ARM ABIs cannot be executed on hosted
-  # runners (no KVM for ARM emulators), so this is a compile-verification step.
-  android-build-arm64:
-      name: Android (aarch64, build)
-      runs-on: ubuntu-latest
-      container: swift:6.3.2
-      steps:
-        - uses: actions/checkout@v4
-        - name: Install Android Swift SDK
-          run: swift sdk install https://download.swift.org/swift-6.3.2-release/android/swift-6.3.2-RELEASE/swift-6.3.2-RELEASE_android-0.1.artifactbundle.tar.gz --checksum 939e933549d12d28f2e0bf71019d734d309859e9773c572657ce565a81f85d68
-        - name: Build tests for Android aarch64
-          run: SWIFT_BLUETOOTH_C_SHIMS=0 swift build --build-tests --swift-sdk aarch64-unknown-linux-android24
-
-  # The official Swift 6.3.2 Android SDK ships only x86_64 and arm64, so 32-bit
-  # ARM (armv7) is cross-compiled with finagolfin's 6.1.3 SDK instead — the
-  # newest community Android SDK whose exact Swift version matches a published
-  # Docker image (Swift SDK .swiftmodule files require an exact compiler match).
-  android-build-armv7:
-      name: Android (armv7, build)
+  # Cross-compile the package and its tests for the ARM ABIs, which cannot be
+  # executed on hosted runners (no KVM for ARM emulators), so these are
+  # compile-verification steps only.
+  #
+  # Both use finagolfin's 6.1.3 SDK — the newest community Android SDK whose
+  # exact Swift version matches a published Docker image (Swift SDK .swiftmodule
+  # files require an exact compiler match). The official swift.org Android SDK is
+  # deliberately not used here: it declares `sdkRootPath: ndk-sysroot` but ships
+  # no sysroot of its own, so it needs a separately installed Android NDK and
+  # fails with "'semaphore.h' file not found" in a plain toolchain container.
+  # (The x86_64 job above can use the official SDK because swift-android-action
+  # installs and wires up the NDK for it.)
+  android-build-arm:
+      name: Android (${{ matrix.arch }}, build)
       runs-on: ubuntu-latest
       container: swift:6.1.3
+      strategy:
+        fail-fast: false
+        matrix:
+          include:
+            - arch: aarch64
+              triple: aarch64-unknown-linux-android24
+            - arch: armv7
+              triple: armv7-unknown-linux-androideabi24
       steps:
         - uses: actions/checkout@v4
         - name: Install Android Swift SDK
           run: swift sdk install https://github.com/finagolfin/swift-android-sdk/releases/download/6.1.3/swift-6.1.3-RELEASE-android-24-0.1.artifactbundle.tar.gz --checksum 440d09d539bda5b94807598b00696ac5d3893cb515b24715ac8868d62130b6d5
-        - name: Build tests for Android armv7
-          run: SWIFT_BLUETOOTH_C_SHIMS=0 swift build --build-tests --swift-sdk armv7-unknown-linux-androideabi24
+        - name: Build tests for Android ${{ matrix.arch }}
+          run: SWIFT_BLUETOOTH_C_SHIMS=0 swift build --build-tests --swift-sdk ${{ matrix.triple }}

Tests/BluetoothTests/GATTTests.swift

@@ -1138,7 +1138,17 @@ struct GATTTests {
                 server.writeValue(data, forCharacteristic: notificationCharacteristic.uuid)
             }
 
-            try await Task.sleep(nanoseconds: 1_000_000)
+            // Notifications are delivered by detached tasks, so a fixed sleep is
+            // racy under CI load — poll until the expected count arrives, up to ~5 seconds.
+            let expectsNotifications = notificationCharacteristic.properties.contains(.notify)
+            for _ in 0..<500 {
+                let receivedCount =
+                    expectsNotifications
+                    ? await notificationData.receivedNotifications.count
+                    : await notificationData.receivedIndications.count
+                if receivedCount >= newData.count { break }
+                try await Task.sleep(nanoseconds: 10_000_000)  // 10ms
+            }
 
             // stop notifications
             try await client.clientCharacteristicConfiguration(