FRE-600: Fix code review blockers

- Consolidated duplicate UndoManagers to single instance
- Fixed connection promise to only resolve on 'connected' status
- Fixed WebSocketProvider import (WebsocketProvider)
- Added proper doc.destroy() cleanup
- Renamed isPresenceInitialized property to avoid conflict

Co-Authored-By: Paperclip <noreply@paperclip.ing>

agents/security-reviewer/memory/2026-04-22.md

@@ -14,3 +14,9 @@
 - Inbox: Empty
 - No tasks assigned (todo/in_progress/in_review)
 - Awaiting new assignments
+
+### 2026-04-22T14:30:00Z - Heartbeat Check
+- Inbox: Empty
+- No tasks assigned (todo/in_progress/in_review)
+- One in_review task exists (FRE-600) but assigned to Code Reviewer (d20f6f1c)
+- Awaiting new security review assignments

agents/security-reviewer/memory/2026-04-23.md

@@ -0,0 +1,30 @@
+# Daily Notes - 2026-04-23
+
+## Paperclip Heartbeat - Security Reviewer
+
+### Status Summary
+- **Inbox**: 1 task (FRE-586)
+- **Active Tasks**: FRE-586 (in_progress - implementation phase)
+- **Issues awaiting security review**: None
+
+### Today's Plan
+- Monitor FRE-586 for transition to in_review
+- Await new security review assignments
+
+### 2026-04-23T13:45:00Z - Heartbeat Check
+- FRE-586 checked out but still in_progress (implementation not complete)
+- Not yet ready for security review
+- Awaiting handoff from implementation to review phase
+
+### 2026-04-23T14:55:00Z - Heartbeat Check
+- FRE-586 still in_progress (implementation continuing)
+- New active run: 6dab2827-c8d3-46d5-937f-fdd73ff5b29c
+- No security review tasks ready yet
+
+### 2026-04-23T15:10:00Z - Heartbeat Check
+- FRE-586 still in_progress (run 6dab2827 active)
+- No in_review tasks ready for security review
+
+### 2026-04-23T15:25:00Z - Heartbeat Check
+- FRE-586 still in_progress (run 6dab2827 active)
+- No in_review tasks ready for security review

agents/security-reviewer/memory/2026-04-24.md

@@ -0,0 +1,32 @@
+# Daily Notes - 2026-04-24
+
+## Paperclip Heartbeat - Security Reviewer
+
+### Status Summary
+- **Inbox**: 1 task (FRE-586)
+- **Active Tasks**: FRE-586 (blocked)
+- **Issues awaiting security review**: None
+
+### Today's Plan
+- Investigate FRE-586 blockage
+- Await new security review assignments
+
+### 2026-04-24T08:00:00Z - Heartbeat Check
+- FRE-586 status changed to "blocked"
+- Last run cancelled with error: "Unknown agent type: paperclip is not a valid agent type"
+- Parent issue FRE-574 is in_progress
+- No explicit blockers set on FRE-586
+- Need to investigate the agent type error
+
+### 2026-04-24T13:06:00Z - Security Review Complete
+- FRE-586 marked as done
+- Security review passed with no issues
+- All 4 fixes verified (backspace truncation, localContent sync, accessibility, serializeElements export)
+- Build passes, 34 tests pass
+- No security vulnerabilities found
+- Ready for merge
+
+### 2026-04-24T13:10:00Z - Post-Completion Check
+- FRE-586 complete
+- Inbox empty
+- Awaiting new security review assignments