terminal-agent could die independently of the server — SIGKILL from the OS
OOM killer, an uncaught exception under PTY churn, an external `pkill` from
a sibling debugging session. Pre-v1.44 the sidebar would observe the broken
connection and stay broken until the user reloaded the sidebar. Now a 60s
ticker checks the recorded agent PID and respawns via the shared
spawnTerminalAgent helper when dead.
Identity-based liveness (T4 from the eng review):
* Uses readAgentRecord + isProcessAlive (signal 0 probe), not a name match.
* Slow-but-alive agents intentionally fall through — respawning around a
living agent would create split-brain (two agents writing the port
file, tokens diverging between them, mystery upgrade 401s).
* Pairs with the v1.44 generation counter in /internal/* loopback calls:
if a stale agent does come back to life mid-cycle, its X-Browse-Gen
no longer matches and the parent's calls 409 cleanly.
Crash-loop guard:
* 3 respawn attempts inside a rolling 60s window → stop trying. A daemon
up for a week with one crash a day shouldn't trip the guard.
* On trip: one-line error to console (`respawn guard tripped`) and the
watchdog goes dormant. Manual restart via the sidebar Restart button
is the explicit signal to re-arm (added in Commit 2 of the larger PR).
Shared spawn path (refactor):
* New spawnTerminalAgent(opts) in terminal-agent-control.ts handles:
prior-PID cleanup → spawn → record stash. Both the CLI cold-start path
in cli.ts and the new server.ts watchdog route through it. Removes the
copy-paste between them; future env wiring lands in one place.
Gated on cfg.ownsTerminalAgent — embedders that pre-launch their own PTY
server (gbrowser phoenix overlay) still own the full lifecycle.
GSTACK_AGENT_WATCHDOG_TICK_MS env knob compresses the 60s tick for e2e
tests without 60s waits per assertion.
Tests:
* browse/test/terminal-agent-watchdog.test.ts — 7 static-grep tripwires
for the load-bearing invariants (ownsTerminalAgent gate, PID-based
liveness, crash-loop guard with window pruning, shutdown cleanup,
CLI cold-start uses the same helper, env knob exists).
* Live process-kill tests belong in the e2e tier; cheaper invariants
here catch refactor regressions in ~1ms each.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Garry Tan