test(ios): keep the busy alert fixture busy for the test's whole alert budget

The fixture's fixed 20 s backstop could stop the in-flight animation while a
contended host was still resolving the alert under the 60 s allowance, so a
correct activation read "Answered after the app went idle". The test now
passes the backstop as resolution allowance plus activation deadline.

Author: thymikee

apple/runner/AgentDeviceRunner/AgentDeviceRunner/AgentDeviceRunnerApp.m

@@ -82,15 +82,21 @@ @implementation AgentDeviceRunnerViewController
 // may receive an event: the app keeps reporting work in flight, which is the state that cost an alert
 // command its whole deadline in #2546. It stops the moment an alert button is answered, since that
 // answer is the event the runner is trying to land, and the backstop stops it even when no answer
-// arrives so a regressed run finishes rather than waiting out XCTest's own timeout. A layer
+// arrives so a regressed run finishes rather than waiting out XCTest's own timeout. The test passes
+// the backstop after `--agent-device-alert-activation-busy`, sized to outlast its whole resolution
+// and activation budget, so a slow host cannot end the busy state before the answer lands. A layer
 // animation on its own is not enough; only a UIView animation counts as in-flight work here.
-static NSTimeInterval const kAgentDeviceAlertActivationBusyWindow = 20.0;
+static NSTimeInterval AgentDeviceAlertActivationBusyWindow(void) {
+  NSArray<NSString *> *arguments = NSProcessInfo.processInfo.arguments;
+  NSUInteger flag = [arguments indexOfObject:@"--agent-device-alert-activation-busy"];
+  return flag + 1 < arguments.count ? arguments[flag + 1].doubleValue : 0;
+}
 
 - (void)startAlertActivationBusy {
   if (self.alertActivationBusyBackstop != nil) {
     return;
   }
-  self.alertActivationBusyBackstop = [NSTimer scheduledTimerWithTimeInterval:kAgentDeviceAlertActivationBusyWindow
+  self.alertActivationBusyBackstop = [NSTimer scheduledTimerWithTimeInterval:AgentDeviceAlertActivationBusyWindow()
                                                                       target:self
                                                                     selector:@selector(stopAlertActivationBusy)
                                                                     userInfo:nil

apple/runner/AgentDeviceRunner/AgentDeviceRunnerUITests/UnitTests/RunnerTests+AlertObservationTests.swift

@@ -60,7 +60,8 @@ extension RunnerTests {
   func testAlertActivationIgnoresAnAppThatNeverSettlesBeforeTheDeadline() throws {
     app.launchArguments = [
       "--agent-device-alert-replacement-regression",
-      "--agent-device-alert-activation-busy"
+      "--agent-device-alert-activation-busy",
+      String(RunnerTests.alertResolutionAllowance + RunnerTests.alertActivationDeadline)
     ]
     app.launch()
     defer {
@@ -72,9 +73,10 @@ extension RunnerTests {
 
     let response = handleAlert(alert, action: "accept", deadline: Date().addingTimeInterval(RunnerTests.alertActivationDeadline))
 
-    // The fixture keeps an animation in flight until a button is answered or its 20 s backstop stops
-    // it, and an in-flight animation is what XCTest waits out before it synthesises an event. An
-    // answer that arrives while the app is still busy is one activation did not wait to idle (#2546).
+    // The fixture keeps an animation in flight until a button is answered or its backstop, which
+    // outlasts resolution plus activation, stops it, and an in-flight animation is what XCTest waits
+    // out before it synthesises an event. An answer that arrives while the app is still busy is one
+    // activation did not wait to idle (#2546).
     XCTAssertTrue(response.ok, String(describing: response.error))
     XCTAssertEqual(app.staticTexts["agent-device-alert-actions"].label, "First actions: 1; replacement actions: 0")
     XCTAssertEqual(app.staticTexts["agent-device-alert-busy-answer"].label, "Answered while busy")