ci: add macOS Xcode build workflow

.github/workflows/xcode-build.yml

@@ -0,0 +1,27 @@
+name: Xcode build
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  macos:
+    name: macOS
+    runs-on: macos-26
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v7
+
+      - name: Build for macOS
+        run: |
+          xcodebuild build \
+            -project potassiumProvider.xcodeproj \
+            -scheme potassiumProvider \
+            -destination 'platform=macOS' \
+            CODE_SIGNING_ALLOWED=NO

doc/TESTING_AND_DEVELOPMENT.md

@@ -110,6 +110,23 @@ xcodebuild test \
 Use `xcodebuild -showdestinations` to copy the exact Mac destination if local
 Xcode requires a more specific macOS variant.
 
+## Continuous Integration
+
+GitHub Actions runs an unsigned macOS build for every pull request and every
+push to `main`. The build uses the `macos-26` runner and its default Xcode 26.5
+installation:
+
+```sh
+xcodebuild build \
+  -project potassiumProvider.xcodeproj \
+  -scheme potassiumProvider \
+  -destination 'platform=macOS' \
+  CODE_SIGNING_ALLOWED=NO
+```
+
+This initial workflow checks compilation only. Unit tests, UI tests, caching,
+and iOS Simulator and visionOS jobs remain outside its scope.
+
 ## Test Style
 
 - New unit tests should use Swift Testing (`import Testing`).

potassiumProvider.xcodeproj/project.pbxproj

@@ -1077,15 +1077,15 @@
 		};
 		C09842BD2FF8491700CB8B7E /* XCRemoteSwiftPackageReference "potassiumChannel" */ = {
 			isa = XCRemoteSwiftPackageReference;
-			repositoryURL = "git@github.com:OpenCow42/potassiumChannel.git";
+			repositoryURL = "https://github.com/OpenCow42/potassiumChannel.git";
 			requirement = {
 				kind = upToNextMajorVersion;
 				minimumVersion = 0.2.0;
 			};
 		};
 		C0DCD8ED2FFA44AB00520215 /* XCRemoteSwiftPackageReference "swift-concurrency" */ = {
 			isa = XCRemoteSwiftPackageReference;
-			repositoryURL = "git@github.com:OpenCow42/swift-concurrency.git";
+			repositoryURL = "https://github.com/OpenCow42/swift-concurrency.git";
 			requirement = {
 				kind = upToNextMajorVersion;
 				minimumVersion = 1.0.1;