Use NSWorkspace to launch app in display resolution UI test

XCUIApplication.launch() hard-fails with a 60-second timeout when
it can't foreground the app on headless CI runners. This test never
uses XCUIApplication for interaction (no taps/keys) — it only reads
a diagnostics file.

Replace with NSWorkspace.openApplication which launches through
Launch Services, passes env vars via OpenConfiguration, and returns
immediately without blocking on activation failure.

Also add CI retry loop since runner environment is flaky.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: austinywang

.github/workflows/ci.yml

@@ -495,12 +495,23 @@ jobs:
           {"helperBinaryPath":"$HELPER_PATH"}
           EOF
 
-          xcodebuild -project GhosttyTabs.xcodeproj -scheme cmux -configuration Debug \
-            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES_DIR" \
-            -disableAutomaticPackageResolution \
-            -destination "platform=macOS" \
-            -only-testing:cmuxUITests/DisplayResolutionRegressionUITests \
-            test
+          for attempt in 1 2; do
+            if xcodebuild -project GhosttyTabs.xcodeproj -scheme cmux -configuration Debug \
+              -clonedSourcePackagesDirPath "$SOURCE_PACKAGES_DIR" \
+              -disableAutomaticPackageResolution \
+              -destination "platform=macOS" \
+              -only-testing:cmuxUITests/DisplayResolutionRegressionUITests \
+              test; then
+              exit 0
+            fi
+            if [ "$attempt" -eq 2 ]; then
+              echo "Display resolution UI regression failed after 2 attempts" >&2
+              exit 1
+            fi
+            echo "Attempt $attempt failed, retrying..."
+            pkill -x "cmux DEV" 2>/dev/null || true
+            sleep 3
+          done
 
       - name: Run browser find focus UI regression
         run: |

cmuxUITests/DisplayResolutionRegressionUITests.swift

@@ -1,5 +1,6 @@
 import XCTest
 import Foundation
+import AppKit
 
 final class DisplayResolutionRegressionUITests: XCTestCase {
     private let defaultDisplayHarnessManifestPath = "/tmp/cmux-ui-test-display-harness.json"
@@ -11,7 +12,7 @@ final class DisplayResolutionRegressionUITests: XCTestCase {
     private var displayDonePath = ""
     private var helperBinaryPath = ""
     private var helperLogPath = ""
-    private var launchedApp: XCUIApplication?
+    private var launchedRunningApp: NSRunningApplication?
     private var helperProcess: Process?
 
     override func setUp() {
@@ -239,18 +240,70 @@ final class DisplayResolutionRegressionUITests: XCTestCase {
         helperProcess = proc
     }
 
+    // Launch the app via NSWorkspace instead of XCUIApplication to avoid
+    // the 60-second foreground activation timeout that kills UI tests on
+    // headless CI runners. NSWorkspace.openApplication passes environment
+    // variables through OpenConfiguration and returns immediately.
     private func launchAppProcess(targetDisplayID: String) throws {
-        let app = XCUIApplication()
-        for (key, value) in launchEnvironment(targetDisplayID: targetDisplayID) {
-            app.launchEnvironment[key] = value
+        let appBundlePath = try resolveAppBundlePath()
+        let appURL = URL(fileURLWithPath: appBundlePath)
+
+        let config = NSWorkspace.OpenConfiguration()
+        config.environment = launchEnvironment(targetDisplayID: targetDisplayID)
+        config.activates = true
+
+        let semaphore = DispatchSemaphore(value: 0)
+        var launchError: Error?
+        var runningApp: NSRunningApplication?
+
+        NSWorkspace.shared.openApplication(at: appURL, configuration: config) { app, error in
+            runningApp = app
+            launchError = error
+            semaphore.signal()
+        }
+
+        let waitResult = semaphore.wait(timeout: .now() + 30.0)
+        if waitResult == .timedOut {
+            throw NSError(domain: "DisplayResolutionRegressionUITests", code: 2, userInfo: [
+                NSLocalizedDescriptionKey: "NSWorkspace.openApplication timed out after 30s for \(appBundlePath)"
+            ])
+        }
+
+        if let error = launchError {
+            throw NSError(domain: "DisplayResolutionRegressionUITests", code: 2, userInfo: [
+                NSLocalizedDescriptionKey: "NSWorkspace.openApplication failed: \(error.localizedDescription) path=\(appBundlePath)"
+            ])
         }
-        app.launch()
-        guard ensureForegroundAfterLaunch(app, timeout: 12.0) else {
+
+        launchedRunningApp = runningApp
+
+        if !waitForAppLaunchDiagnostics(timeout: 15.0) {
+            let isAlive = launchedRunningApp?.isTerminated == false
             throw NSError(domain: "DisplayResolutionRegressionUITests", code: 2, userInfo: [
-                NSLocalizedDescriptionKey: "XCUIApplication failed to reach foreground. state=\(app.state.rawValue)"
+                NSLocalizedDescriptionKey: "App failed to write launch diagnostics. alive=\(isAlive) diagnostics=\(loadDiagnostics() ?? [:])"
             ])
         }
-        launchedApp = app
+    }
+
+    private func resolveAppBundlePath() throws -> String {
+        // UI test bundle is at:
+        //   .../Build/Products/Debug/cmuxUITests-Runner.app/Contents/PlugIns/cmuxUITests.xctest
+        // The app is at:
+        //   .../Build/Products/Debug/cmux DEV.app
+        let testBundle = Bundle(for: Self.self)
+        let productsDir = testBundle.bundleURL
+            .deletingLastPathComponent()  // -> .../Contents/PlugIns
+            .deletingLastPathComponent()  // -> .../Contents
+            .deletingLastPathComponent()  // -> .../cmuxUITests-Runner.app
+            .deletingLastPathComponent()  // -> .../Debug
+        let appPath = productsDir.appendingPathComponent("cmux DEV.app").path
+        if FileManager.default.fileExists(atPath: appPath) {
+            return appPath
+        }
+
+        throw NSError(domain: "DisplayResolutionRegressionUITests", code: 4, userInfo: [
+            NSLocalizedDescriptionKey: "App bundle not found at \(appPath). testBundle=\(testBundle.bundleURL.path)"
+        ])
     }
 
     private func launchEnvironment(targetDisplayID: String) -> [String: String] {
@@ -264,31 +317,32 @@ final class DisplayResolutionRegressionUITests: XCTestCase {
     }
 
     private func terminateLaunchedAppIfNeeded() {
-        guard let launchedApp else { return }
-        defer { self.launchedApp = nil }
-
-        if launchedApp.state == .notRunning {
-            return
+        guard let app = launchedRunningApp else { return }
+        defer { launchedRunningApp = nil }
+
+        if app.isTerminated { return }
+        app.terminate()
+        let deadline = Date().addingTimeInterval(5.0)
+        while !app.isTerminated && Date() < deadline {
+            RunLoop.current.run(until: Date().addingTimeInterval(0.1))
+        }
+        if !app.isTerminated {
+            app.forceTerminate()
         }
-
-        launchedApp.terminate()
-        _ = launchedApp.wait(for: .notRunning, timeout: 5.0)
     }
 
     private func launchedAppDiagnostics() -> String {
-        guard let launchedApp else { return "not-launched" }
-        return "state=\(launchedApp.state.rawValue)"
+        guard let app = launchedRunningApp else { return "not-launched" }
+        return "pid=\(app.processIdentifier) terminated=\(app.isTerminated)"
     }
 
-    private func ensureForegroundAfterLaunch(_ app: XCUIApplication, timeout: TimeInterval) -> Bool {
-        if app.wait(for: .runningForeground, timeout: timeout) {
+    private func waitForAppLaunchDiagnostics(timeout: TimeInterval) -> Bool {
+        waitForCondition(timeout: timeout) {
+            guard let diagnostics = self.loadDiagnostics() else { return false }
+            guard let pid = diagnostics["pid"], !pid.isEmpty else { return false }
+            guard let stage = diagnostics["stage"], !stage.isEmpty else { return false }
             return true
         }
-        if app.state == .runningBackground {
-            app.activate()
-            return app.wait(for: .runningForeground, timeout: 6.0)
-        }
-        return false
     }
 
     private func waitForTargetDisplayMove(targetDisplayID: String, timeout: TimeInterval) -> Bool {