Adds behavior detail to the existing 'Externally managed Camofox sessions'
subsection in features/browser.md:
- Three-row settings table (config key + env var + effect).
- 'What changes when user_id is set' — soft-cleanup behavior, why
DELETE /sessions/<user_id> is skipped.
- 'How tab adoption works' — 4-step lookup against GET /tabs, listItemId
matching, fallback to new-tab creation, no mid-run re-polling.
- Picking session_key: how to attach to a specific existing tab vs
share-profile-only behavior with the default per-task session_key.
- Concurrency note that Camofox does not arbitrate per-tab focus.
38441a7d77