CodePilot/docs/agent-tooling-todo-bridge.md

Agent Tooling & TodoWrite Bridge

Architecture Overview

SDK TodoWrite tool_use
  → PostToolUse hook (claude-client.ts)
    → Emits tool_result SSE (deduped)
    → Emits task_update SSE { session_id, todos[] }
      → collectStreamResponse (route.ts)
        → syncSdkTasks() persists to DB
      → Frontend SSE consumer (useSSEStream.ts)
        → onTaskUpdate dispatches 'tasks-updated' event
          → TaskList re-fetches from /api/tasks

TodoWrite Field Mapping

SDK TodoWriteInput field	Local tasks table column	Notes
(array index)	id (prefixed sdk-{sessionId}-{index})	Full sessionId avoids collision
content	title	Main display text
status	status	Mapped via mapStatus()
activeForm	description	Present-continuous form label
(array index)	sort_order	Preserves original order

Status Mapping

SDK status	Local TaskStatus
pending	pending
in_progress	in_progress
completed	completed
Other	pending

Idempotency

syncSdkTasks() uses a replace-all strategy within a transaction:

1. DELETE FROM tasks WHERE session_id = ? AND source = 'sdk'
2. INSERT all todos from the latest TodoWrite payload

This is naturally idempotent — calling it multiple times with the same data produces identical results. User-created tasks (source = 'user') are never affected.

tool_result Two-Layer Last-Wins Dedup

Both PostToolUse hook and user message handler in the SDK can emit the same tool_result. PostToolUse fires first (for immediate UI feedback); the user handler's result may be more complete/canonical. Strategy: both sources emit freely; consumption layers use "last wins" (replace, not skip) so the most complete result is always kept.

Layer 1: route.ts (DB persistence)

• seenToolResultIds Set in collectStreamResponse() — when a duplicate tool_use_id arrives, the existing contentBlock entry is replaced with the newer result.

Layer 2: ChatView.tsx (UI state)

• onToolResult finds existing entry by tool_use_id and replaces it instead of appending a duplicate.

SSE Event Types

Event	Source	Purpose
text	stream_event	Streaming text delta
tool_use	assistant message	Tool invocation
tool_result	PostToolUse / user	Tool execution result (deduped)
tool_output	stderr callback	Raw tool output
tool_timeout	tool_progress	Tool execution timeout
task_update	PostToolUse	TodoWrite sync trigger
status	system message	Session init, notifications
result	result message	Final result with usage stats
permission_request	canUseTool	Permission approval needed
mode_changed	system status	SDK mode change
error	catch block	Error occurred
done	stream end	Stream complete

Troubleshooting

Tasks not appearing after TodoWrite

1. Check server console for [claude-client] logs — ensure PostToolUse fires
2. Verify task_update SSE event in browser DevTools Network tab
3. Check syncSdkTasks() runs in collectStreamResponse (server-side tee'd stream)
4. Verify tasks-updated CustomEvent fires in browser console

Duplicate tool results

1. Check emittedToolResultIds Set size in server logs
2. Compare SSE event count before/after (should be halved for tools)
3. Query messages table: SELECT content FROM messages WHERE content LIKE '%tool_result%' — each tool_use_id should appear once

SDK upgrade issues

• Current: v0.2.62 (upgraded from v0.2.33)
• Rollback: npm install @anthropic-ai/claude-agent-sdk@0.2.33
• Key integration points: canUseTool, PostToolUse, Notification, tool_progress, system, result