- Add debugLog import from helpers
- Log toolName, toolCallId, and relevant params for each tool:
  - subagent_with_context: async, taskLength, persona, model, cwd, notifyOnComplete, maxAge
  - subagent_isolated: same params as above
  - get_subagent_status: jobId
  - get_subagent_result: jobId
  - cancel_subagent: jobId
  - list_available_models: authOnly, filter
  - prune_subagent_jobs: none
- Enable via SUBAGENT_DEBUG_LOG_DIR env var
- Logs to JSONL files (debug-YYYY-MM-DD.jsonl) with timestamps