docs: add session notes with honest retrospective

This document captures our collaboration journey, including bugs found,
decisions made, and honest assessment of what went well and what didn't.

Key points:
- Optimistic updates were essential for good UX
- User caught two bugs during review (DELETE method, epic filter)
- Test coverage helped ensure correctness throughout

.beads/SESSION_NOTES.md

@@ -0,0 +1,85 @@
+# Session Notes: Assign Archetypes to Tasks - UI System
+
+## Executive Summary
+Implemented a complete UI system for assigning agent archetypes to tasks
+via both graph nodes and sidebar panel.
+
+## Collaboration Journey
+
+### 1. Initial Discovery (User Question: "What did we do so far?")
+We reviewed the current state and found partial implementation of the
+assign archetypes feature. The epic had 4 child tasks:
+- beadboard-yo5: Pass labels to graph nodes ✓
+- beadboard-brq: Add Assign button/dropdown ✓
+- beadboard-7r7: Visual indicators (partial)
+- beadboard-b7t: Enhance AssignmentPanel (not started)
+
+### 2. Bug Discovery: Unassign Not Working
+User reported: "I see 'unassigned <archetype>' but it's still showing as a tag"
+
+**Root Cause**: DELETE API existed but frontend was calling POST for unassign.
+
+**Fix**: Changed handleUnassignAgent to use method: 'DELETE'
+
+**Deeper Issue**: Even with correct API, UI didn't update because props
+don't change after client-side API calls.
+
+**Final Solution**: Implemented optimistic UI updates with localLabels state.
+
+### 3. Missing Epic Filtering
+User feedback: "needs agent area should be filtered to selected epic"
+
+We had correctly implemented epic filtering for Squad Roster but forgot
+to apply it to Needs Agent and Pre-assigned sections.
+
+### 4. Honest Mistakes Made
+1. Initially used POST for unassign instead of DELETE
+2. Forgot epicId filter on new sections (caught by user)
+3. First implementation didn't consider optimistic updates
+
+## Technical Decisions
+
+### Why Optimistic Updates?
+- Instant feedback for better UX
+- Rollback on error preserves data integrity
+- Avoids full page refresh or complex re-fetch patterns
+
+### Why useGraphAnalysis Hook?
+- Single source of truth for "actionable" definition
+- Reused across SmartDag and AssignmentPanel
+- Ensures consistency: a task is actionable everywhere or nowhere
+
+### Label Format: `agent:<archetypeId>`
+- Simple string format
+- Easy to parse and filter
+- Works with existing bd label commands
+
+## Files Changed (Summary)
+- graph-node-card.tsx: Assign UI + optimistic updates
+- assignment-panel.tsx: Three-section sidebar
+- workflow-graph.tsx: Pass labels to nodes
+- smart-dag.tsx: Main view with assign mode
+- unified-shell.tsx: Wire up sidebar panel
+- use-graph-analysis.ts: Shared analysis logic
+- API route: Added DELETE handler
+
+## Beads Closed
+- beadboard-yo5 ✓
+- beadboard-brq ✓
+- beadboard-7r7 ✓
+- beadboard-b7t ✓
+- beadboard-lgi (Epic) ✓
+
+## Test Coverage
+- 6 tests for graph node assign
+- 5 tests for assignment panel sections
+- 4 tests for graph node labels
+- 12 tests for SmartDag
+- 6 tests for useGraphAnalysis
+- 9 tests for UnifiedShell
+
+## What's Next
+From `bd ready`:
+- beadboard-58u (P3): DependencyFlowStrip
+- bb-18e.1 (P2): Cycle warning card
+- bb-18e.2 (P1): Plain-English edge labels