platform-ios: reduce XCTest agent per-tick cost on constrained hosts

[V3RON]

Context

Harness runs unreliably on small CI hosts (e.g. GitHub macos-latest: 3 vCPU / 7 GB). One constant source of load inside the simulator is the XCTest agent's tick loop.

Every tick (default 1 s, HarnessXCTestAgentUITests.swift testAgentSession) does:

• observeTargetApplication() → targetApplication.state query
• PermissionPromptWatchdog.tick() → springboard.buttons.matching(NSPredicate(label IN ...)).firstMatch.exists

The SpringBoard query is a full accessibility-tree snapshot served by testmanagerd, so the sim pays for an AX snapshot every second for the whole run — including during the app's launch/connect window, which is exactly when the host is most starved. configurePermissions is sent right at ensureStarted (packages/platform-ios/src/xctest-agent.ts), so auto-accept polling is active before the app under test has even been launched.

Proposal

1. Only run the watchdog query when the target app is .runningForeground (skip while it is not running / launching).
2. Defer enabling autoAcceptPermissions until the app has reported ready over the bridge, rather than at agent start.
3. Make the tick interval host-adaptive: the CLI already forwards HARNESS_XCTEST_AGENT_TICK_INTERVAL_MS; derive a default (e.g. 2–3 s) from getHostCapabilities() on constrained hosts instead of the fixed 1 s.
4. Cheapen the probe: check springboard.alerts.firstMatch.exists first and only enumerate buttons when an alert is present.

Files

• packages/platform-ios/xctest-agent/HarnessXCTestAgentUITests/HarnessXCTestAgentUITests.swift
• packages/platform-ios/xctest-agent/HarnessXCTestAgentUITests/PermissionPromptWatchdog.swift
• packages/platform-ios/src/xctest-agent.ts (getLaunchEnvironment, ensureStarted)
• packages/platform-ios/src/xctest-agent-capabilities.ts

Part of a broader effort to make Harness reliable on constrained CI runners.