Only reap browsers that have sent at least one `system.heartbeat`.
A pre-heartbeat extension never opts in, so it is never dropped on
silence and keeps relying on socket-close detection exactly as before.
This removes a backward-compat regression where a new daemon paired
with an old extension would wrongly reap a live-but-idle connection
and then report `no_browser_connected` on the next command.
- Add a `heartbeat_seen` flag to `BrowserClient`, set when a heartbeat
event arrives, and exclude never-heartbeated clients from
`stale_browsers`.
- Cover both the opt-in and the legacy-survivor cases in unit tests.
Co-authored-by: Cursor <cursoragent@cursor.com>
Introduce a `system.heartbeat` protocol event and use it as a
liveness signal on the daemon side.
- Track `last_seen` per connected browser, bumped on every inbound
WS frame (tool response, event, ping/pong, or heartbeat).
- Add a reaper task that drops any browser silent past a 60s window
and purges its sessions, mirroring the WS disconnect cleanup. This
releases half-open connections left behind when the OS resumes from
sleep and kills the service worker without delivering a close frame,
so the daemon no longer pins a phantom "connected" browser and can
idle-exit normally.
- Wire the reaper into both the foreground daemon and the test/embed
entry point, aborting it on shutdown.
Co-authored-by: Cursor <cursoragent@cursor.com>
