💭 fix: Show the Thoughts Floating Bar Only When Its Header Is Off Screen

[berry-13]

Summary

Part 3 of the ui-refinments stack (#16640 onto dev, then #16641, #16642, #16643; merge from the bottom up).

The Thoughts block showed its floating collapse and copy bar even while the Thoughts header was plainly on screen, because the bar trusted the last IntersectionObserver entry, and an entry recorded while the block was still opening could arrive after it settled and claim the header was hidden. The bar now re-measures the header's real position, clipped against the viewport and every scrolling ancestor, on each observer notification and whenever the pointer or focus reveals the bar, so it appears only once the header has scrolled away.

Pressing and holding the Thoughts header no longer flashes a background, and the block drops the extra bottom padding it reserved for the bar.

Type of change

• Bug fix

Testing

Tested environments/configuration:

• Browser: Chromium (Playwright) against a local dev server, light and dark mode
• Opened Thoughts in the first and second reply with the pointer resting on the header, then hovered the body and moved out and back: the bar stayed hidden in every case

Automated tests:

• npx jest --findRelatedTests on the changed files
• npx tsc --noEmit -p client/tsconfig.json, ESLint, Prettier, npm run static-checks

Screenshots / recordings

Captured from the e2e mock harness at 1280x800 against the client built before and after this PR.

	Before	After
Open Thoughts, pointer over the body, light
Header held down, light
Open Thoughts, pointer over the body, dark
Header held down, dark

Risk / compatibility

None.

Checklist

• I reviewed my own changes
• Existing relevant tests pass
• The change does not introduce new warnings or errors

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-02T21:17:09.079293Z	02b5f7e	New commits
🔒 Security Review	✅ Completed 2026-10-01T22:21:16.719323Z	0e1bad4	PR opened

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