fn-9.6 Log watcher and parser lib

fn-9.6 Log watcher and parser lib

Description

Create log watcher and stream-json parser for iter-*.log files.

Files

• src/lib/log-watcher.ts - fs.watch wrapper
• src/lib/parser.ts - stream-json format parser

LogWatcher

class LogWatcher extends EventEmitter {
  constructor(runPath: string)
  start(): void
  stop(): void
  // Events: 'line', 'error', 'new-iteration'
}

Watching strategy

1. Watch run directory for new iter-*.log files
2. Tail-follow current iteration log
3. Debounce file change events (100ms)
4. Track byte position for incremental reads

Parser

stream-json format (from Claude --watch):

{"type":"tool_call","tool":"Read","input":{...}}
{"type":"tool_result","content":"..."}
{"type":"text","content":"..."}

Parse into LogEntry with tool icons:

• Read/Write/Glob → →
• Bash → ⚡
• API calls → ◆
• success → ✓
• failure → ✗

Testing strategy

Parser tests (pure function, easy to test):

• Unit test: JSON line → LogEntry mapping
• Test various tool types, malformed lines

LogWatcher tests (I/O, harder):

• Use temp directory with test log files
• Append content, verify 'line' events fire
• May need polling fallback on some platforms

Acceptance

• LogWatcher emits 'line' events for new log content
• Detects new iter-*.log files appearing
• Parser extracts tool type and content from stream-json
• Parser assigns correct icons per tool type
• Handles malformed JSON lines gracefully (skip, don't crash)
• stop() properly cleans up watchers

Done summary

• Added LogWatcher class with fs.watch for run directory and iter-*.log files
• Added parser for stream-json format with tool icons (unicode + ASCII)
• Implemented debounced reads, byte position tracking, iteration detection
• Full test coverage (42 tests)

Evidence

• Commits: ccd55aeb0edcfb8a235b22158aa83ce1c53c7bf1
• Tests: bun test
• PRs: