Pre-v1.44 `$B connect` was fire-and-forget: spawn server detached, CLI
exits, server runs unsupervised. If the server crashed (OOM, uncaught
exception, signal kill from a runaway debugger), the user had to notice,
re-run `$B connect`, and resume work. The v1.44 terminal-agent watchdog
recovers from one layer of failure; this commit closes the outer loop.
Opt-in via `--supervise` flag or `BROWSE_SUPERVISE=1` env. Default
behavior is unchanged — every existing caller (Claude Code's Bash tool,
scripts, CI) still gets a prompt return. When the flag is set:
* CLI stays attached, polls server PID every 30s via readState() +
isProcessAlive (same identity primitive as the terminal-agent watchdog).
* On unexpected exit: respawn via the same headed-mode startServer path
used initially, then re-spawn the terminal-agent so the PTY recovers
too (otherwise sidebar Restart is the only path back).
* Crash-loop guard: 5 respawns in a rolling 5-min window → exit 1 with
a clear error. Window pruning means a long-lived daemon with sporadic
crashes does NOT trip the guard (otherwise we punish the user for the
supervisor doing its job).
* Backoff: 1s, 2s, 4s, 8s, 30s capped. Env-overridable via
GSTACK_SUPERVISOR_BACKOFF for tests.
* SIGINT / SIGTERM: clean teardown — signals the supervised server
before exiting itself. Without this, Ctrl-C leaves an orphaned server.
Out of scope (deferred follow-up): routing the Chromium-disconnect
exit-code-1 path back through this supervisor. The terminal-agent
watchdog already covers the highest-frequency restart case; Chromium
crash recovery joins the queue as its own commit.
Test (browse/test/cli-supervisor.test.ts):
* 6 static-grep tripwires: opt-in default, signal wiring, crash-loop
guard with window pruning, backoff schedule env knob, tick interval
env knob, terminal-agent re-spawn after server respawn.
* Live respawn tests belong in the e2e tier (real spawn cycles take
3-8s each; spamming these in the free tier would balloon CI time).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Garry Tan