[codex] Restore notebook cell focus

[jlewi]

Summary

• persist per-notebook active cell UI state in localStorage
• restore focus only for the visible notebook tab instead of replaying a restore counter
• reopen markdown cells in editor mode on refresh when the editor was the last active surface
• persist markdown editor focus explicitly when Monaco takes focus, so markdown reload restores the editor reliably
• add a design note and a Chromium CUJ scenario for notebook focus persistence

Why

Switching away from the browser tab while editing markdown caused the cell to blur back into rendered mode, which made note-taking and copy/paste workflows awkward. The original counter-based restore path was also fragile because unrelated re-renders could replay restore logic. Persisting { docUri -> activeCellId, focusRole } gives a simpler model and better refresh behavior.

Design

• docs-dev/design/20260514_notebook_focus_persistence.md

Validation

• runme run build test
• pnpm -C app exec vitest run src/components/Actions/Actions.test.tsx src/components/Actions/MarkdownCell.test.tsx src/lib/notebookActiveCellState.test.ts
• pnpm -C app exec tsc --target es2020 --module nodenext --moduleResolution nodenext --esModuleInterop --skipLibCheck --outDir test/browser/.generated test/browser/test-scenario-notebook-focus-persistence.ts
• CUJ_FRONTEND_URL=http://localhost:4173 node app/test/browser/.generated/test-scenario-notebook-focus-persistence.js
• Chromium walkthrough artifact: app/test/browser/test-output/scenario-notebook-focus-persistence-walkthrough.webm

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Gate focus-restore effect to new requests only

This effect re-applies restore logic whenever value changes while restoreFocusRequest > 0, so after a single restore event the markdown cell can be forced back into rendered mode on each keystroke when restoreFocusRole is "rendered". In practice: focus a rendered markdown cell, switch away and back (request increments), then enter edit mode and type — the value update retriggers this effect and immediately flips the cell out of the editor. The restore behavior should run only when the request counter changes, not on content edits.

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