docs(bf-dm8v): note that feature was already complete

The OOM event detection and alert banner was implemented in commit ea1406a.
This notes file documents the implementation summary.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

notes/bf-dm8v.md

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+# OOM Event Detection - Already Complete
+
+This task (bf-dm8v) was already implemented in commit `ea1406a` on 2026-06-07.
+
+## Implementation Summary
+
+The OOM event detection and alert banner feature was fully implemented with:
+
+### Backend (systemCgroupMonitor.ts)
+- `getOomState()` function for lightweight OOM polling
+- Tracks: `oomKillCount`, `lastOomAt`, `oomDetected`, `memoryCurrentAtOom`
+- Reads from `/sys/fs/cgroup/user.slice/user-1001.slice/memory.events`
+
+### API (server.ts)
+- `GET /api/system/oom-state` endpoint returns current OOM state
+- Includes `formattedMemoryCurrent` for human-readable memory value
+
+### Frontend (OomAlertBanner.tsx)
+- Polls `/api/system/oom-state` every 30 seconds
+- Shows persistent red alert banner when `oomDetected=true`
+- Displays: OOM kill count, timestamp, memory at detection
+- Dismissible via X button
+- Auto-clears after 1 hour using localStorage
+- CSS styling: red background, warning icon, dismiss button
+
+### Integration (App.tsx)
+- Banner rendered at top of dashboard (line 640)
+- `oomBannerDismissed` state tracks dismissal
+
+## Files Modified in ea1406a
+- `src/systemCgroupMonitor.ts` - +66 lines (getOomState, OomState interface)
+- `src/web/server.ts` - +11 lines (/api/system/oom-state endpoint)
+- `src/web/frontend/src/components/OomAlertBanner.tsx` - +115 lines (new component)
+- `src/web/frontend/src/App.tsx` - +3 lines (import and render)
+- `src/web/frontend/src/index.css` - +68 lines (banner styling)
+
+Total: 263 lines added