[turinglambdaai]

Diagnostic prerequisite for #329 (macOS embedded backend startup spin).

• At the first AX window timeout in the packaged native UI test, the reference driver captures an exact-process ps snapshot only under GitHub CI.
• If the affected app's CPU usage remains >=200%, attempt a bounded three-second macOS sample for that exact PID. Include sample or permission-error evidence in the already-uploaded if: always() native UI artifacts.
• Preserve the original test failure, avoid sampling unrelated apps and do not apply automatic crash-kill or unbounded retries.
• Document the evidence contract and privacy limitations. This is not a root-cause fix and does not close embedded runtime: intermittent startup spin (window never renders) and packaged-app orderly-exit semantics contradict the docs #329 until a genuine wedge sample identifies and verifies the runtime change.

Starting Rivet main SHA: 675d0ba68858347dec393022048e299b7482e580.
Maintainer inputs re-read: AGENTS.md and docs/desktop-closeout-mobile-plan.md; current central policy repository SHA 2203a927b9947d3ab6f3e9cad9f2892d4f199497 (PRODUCT-STANDARD.md, DOCUMENTATION-LANGUAGES.md, PORTFOLIO.md). Native macOS CI must compile/run.