Server side (browser-manager.ts):
Idempotent threshold tracker fires an activity entry exactly once at
each upward crossing of 50 (soft warn) and 200 (hard warn). Re-arms
when the count drops below. Activity-feed surface gives the
audit-trail invariant even with the sidebar closed; the toast UX
lives in the sidebar.
Sidebar side (extension/sidepanel.{html,css,js}):
Every /memory poll evaluates two trigger conditions:
- Any single tab > 4 GB JS heap (catches the WebGL/video runaway
case Codex flagged on the eng review).
- Tab count >= 200.
Toast shows top 5 tabs ranked by max(jsHeap, nodes*1KB + listeners*200)
so a WebGL-heavy tab with small JS heap still surfaces. Default-selected
checkboxes + "Close selected" run \`\$B closetab <id>\` through the
existing /command path — no chrome.tabs.remove bridge needed. "Snooze"
bumps tabsAbove/heapAbove thresholds in chrome.storage.session so the
toast stays hidden until the user accumulates more tabs OR one tab
grows another 2 GB.
Tests: browse/test/tab-guardrail.test.ts pins the server-side
fires-once + re-arms invariants without spinning up Chromium.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Garry Tan