[tmashara]

A before hook whose click lands but does nothing (before hydration, or on the wrong element) shoots the closed state on both sides, and they match. Nothing about it looks wrong.

This adds no expect route field. A hook that throws is already a route error naming the side and hook (before hook failed on left: …), and it is never retried. So ending the hook with await page.locator(sel).waitFor({ timeout: 5_000 }) already gives "state not reached". The only gap an expect checked at shot time would close is state that the settle's scroll pass undoes after a before hook. beforeShot already covers that: open and assert there, and nothing runs between the assertion and the shot. A new key would add validation, dedupe, cache-key and error-path code for a single Playwright line, and it would only handle selector assertions.

Changes:

• docs/scoping.md: the menu route example now ends with waitFor. A new paragraph says when to guard (optional things like a cookie banner) and when not to (the state under test). It also notes that waitFor is strict (use a unique selector or .first()), shows what a miss looks like, and says to move to beforeShot when the scroll pass could undo the state.
• skills/renderdiff/reference.md: the hooks bullet gets the waitFor line, and the before hook failed errors row explains what locator.waitFor: Timeout means.
• skills/renderdiff/SKILL.md: the open-menus note points to a hook that ends waiting for the open state.

Verification: npm run format:check and npm test pass (360/360). Nothing under src/ changed, so I skipped the visual tier.

Fixes #103

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