describe_page

Args:
    wait_stable: if True, install a MutationObserver and wait until the
        DOM has been quiet for `stable_ms` before snapshotting (max
        `max_wait` seconds). Use on SPA / lazy-rendered pages so the
        LLM sees the final state, not a half-hydrated render. Cheap
        (~50-200ms typical, capped at max_wait).
    max_wait: outer cap for stability wait (default 2.5s)
    stable_ms: required quiet window in ms (default 400)

Output shape:
  {
    "title": "...",
    "url": "...",
    "headings": [{"level":"h1","text":"..."}],
    "fields": [{"label":"...","type":"text|email|...","required":bool,"value":"...","name":"...","id":"..."}],
    "actions": [{"text":"Submit","kind":"button","disabled":false}],
    "errors": ["..."],
    "navigation": ["Dashboard","Settings",...],
    "stability": "stable|timeout|skipped"  (only present if wait_stable=True)
  }

Use this BEFORE smart_fill so the LLM knows which labels exist.