Add wait_for_agent MCP tool that blocks until an agent reaches a terminal
state (completed, failed, stopped). Returns final status with session_id,
worktree_path, and git commits made by the agent.
- Subscribe-before-check pattern avoids race conditions
- Handles lagged receivers, channel closure, and configurable timeout
- Default timeout 5 minutes, includes git log of agent commits in response
- 11 new tests covering all paths
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>