PTY connections were dying silently after NAT idle timeouts (30-60s on most
home routers, even shorter on some carrier-grade NAT) and Chrome MV3 panel
suspension. Neither side noticed until the user's next keystroke produced
no output. Both sides now drive a 25s keepalive cycle.
Server side (browse/src/terminal-agent.ts):
* New ws.open handler constructs the PtySession eagerly and starts a
setInterval that sends `{type:"ping",ts:Date.now()}` every 25s.
Interval handle stored on session.pingInterval so close() can clear it.
* PtySession.pingInterval field added; cleared in ws.close before
disposeSession runs. Prevents timer leak across reconnects.
* Message handler accepts `{type:"ping"|"pong"|"keepalive"}` silently —
keepalive frames are a liveness signal at the TCP layer, no state to
update. Existing resize/tabSwitch/tabState handling unchanged.
* GSTACK_PTY_KEEPALIVE_INTERVAL_MS env knob (default 25000) lets the
upcoming e2e tests compress idle assertions without 30s waits.
Client side (extension/sidepanel-terminal.js):
* Belt-and-suspenders: client also runs a 25s setInterval that sends
`{type:"keepalive"}`. Defends against Chrome pausing our timers if
the server-side ping ever gets dropped (rare but possible in MV3).
* Ping reply: on `{type:"ping",ts}` from the server, immediately send
`{type:"pong",ts}`. Lets the agent observe round-trip latency for
free and confirms the channel is bidirectional.
* Interval cleared in three teardown paths: ws.close handler,
teardown(), forceRestart(). Three paths exist because the sidebar
can exit the LIVE state through any of them; all three must clean up
or we leak timers across reconnects.
Test (browse/test/terminal-agent-keepalive.test.ts):
* Static-grep tripwires for the 7-point protocol contract: agent has
a configurable interval, open() starts the ping, close() clears it,
message handler accepts keepalive vocabulary, client sends keepalive
+ replies pong, and all three client teardown paths clear the timer.
* Wire-level tests (actually observe a ping after 25s) belong in the
e2e tier — adding them here would either flake on slow CI or require
a real Bun.serve listener per test which we don't want to pay for
in the free tier.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Garry Tan