Replace file watcher with Claude Code hook for todo/plan detection

[dang-hai]

Summary

Replace the current file watcher-based todo detection with a proper hook-based approach once Claude Code provides the necessary hooks.

Current Implementation (File Watcher - Unreliable)

File	Purpose
apps/desktop/src/main/services/session-watcher/SessionFileWatcher.ts	Uses fs.watch to monitor .jsonl session files
packages/shared/src/parsers/todo-extractor.ts	Parses JSONL files to find TodoWrite tool calls
apps/desktop/src/renderer/hooks/useSessionFileWatcher.ts	React hook subscribing to file change events
apps/desktop/src/renderer/hooks/useSessionOverview.ts	Integrates file watching with todo extraction

How it works now:

1. SessionFileWatcher uses Node.js fs.watch to detect .jsonl file changes
2. Debounces rapid writes (300ms base, 1000ms max) to handle streaming
3. On change, useSessionOverview re-reads and parses the entire JSONL file
4. extractLatestTodoList() scans from the end to find the latest TodoWrite tool_use block
5. Converts to TodoListProgress for UI rendering

Problems:

• Inefficient: Must re-parse entire session file on every change
• Complex debouncing: 300ms/1000ms timing to handle streaming writes
• No granularity: Can't distinguish message changes from todo updates
• No plan detection: No way to detect when a plan is created
• Timing issues: Missed updates or duplicate processing

Desired Solution

Use Claude Code's hook system with PostToolUse matcher for TodoWrite:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": {
          "tool_name": "TodoWrite"
        },
        "command": "notify-agent-base"
      }
    ]
  }
}

Benefits:

• Real-time notifications without file polling
• Todo content delivered directly in hook payload (no parsing needed)
• React only to todo changes, not every session update
• Cleaner, more reliable architecture

Blockers

Claude Code does not currently have a dedicated hook for todo/plan creation.

Available hooks per DeepWiki:

• PreToolUse / PostToolUse - could work if payload includes tool input
• No dedicated TodoCreated or PlanCreated hook

Questions for Anthropic:

1. Does PostToolUse include the tool's input (todo list content) in its payload?
2. Is there a separate "plan" concept with its own tool, or is it all TodoWrite?

Action Items

• Investigate if current PostToolUse hook provides enough data
• If not, request feature from Anthropic (anthropics/claude-code)
• Once hooks are available, refactor to use hook-based approach
• Remove file watcher complexity

Related Files

apps/desktop/src/main/services/session-watcher/
├── SessionFileWatcher.ts
├── index.ts
└── ipc.ts

packages/shared/src/parsers/
├── todo-extractor.ts
└── types.ts

apps/desktop/src/renderer/hooks/
├── useSessionFileWatcher.ts
└── useSessionOverview.ts