When a tool container stops, the docker exec PTY reaches EOF. Previously,
the event-driven reader silently returned on EOF, leaving websockets
attached to a dead session. Input writes then failed silently.
Changes:
- _on_fd_readable: detect EOF (empty read) and call _handle_eof()
- _handle_eof: stop reading, mark process dead, close all websockets
with code 4001 to force frontend reconnection
- write_input: detect write errors and trigger EOF cleanup
Quality gates: pytest (19 passed, 1 skipped)
Alex Blank
37134b8c18