File watchers for reactive session events

[evansenter]

Summary

Add file system watchers that emit events during a session, enabling reactive behavior when files change.

Use Cases

• Test-driven development: Automatically re-run tests when source files change
• Build monitoring: React to build output/errors as they occur
• Log tailing: Surface relevant log entries during debugging
• External tool integration: React to files written by other processes

Considerations

• Watch scope: Which paths to watch, how to configure
• Event filtering: Debouncing, ignoring irrelevant changes (node_modules, .git)
• Session lifecycle: Start/stop watchers, cleanup on exit
• Event integration: How watcher events feed into the agent loop

Implementation Options

1. notify crate: Rust file system notification library
2. Manual polling: Simpler but less efficient
3. OS-specific: inotify (Linux), FSEvents (macOS), ReadDirectoryChangesW (Windows)

Status

🔮 Speculative - This is a future consideration for reactive/agentic workflows. Not needed for current interactive use cases.

Related

• Consider streaming-first architecture for subagents and background operations #59 - Streaming-first architecture (parent RFC)
• RFC: MCP client integration (connect to external MCP servers) #3 - MCP integration and agent spawning