- Replace blocking stdout.read() with select()-based non-blocking reads
so the decode thread responds to stop within 0.5s
- Make stop() non-blocking by releasing the lock before terminating the
process and removing the redundant wait()
- Move initial scanning SSE event from start() into the decode thread so
it fires after the frontend EventSource connects
- Update frontend stop() to give immediate UI feedback before the fetch
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>