Problem

On Windows, a connected headed browse session blinks a conhost.exe console window on a fixed interval for the entire session — no CLI command, no user action. The terminal-agent watchdog calls isProcessAlive() once per setInterval tick (default 60s) to check the agent PID, and on Windows isProcessAlive() shelled out to tasklist, which Windows gives its own console window. macOS/Linux stayed silent because their branch is a process.kill(pid, 0) syscall that spawns nothing.

It is purely cosmetic — each window self-closes — but it blinks on a fixed interval for the whole session with no indication of what it is.

Root cause

isProcessAlive() (browse/src/error-handling.ts) had a Windows-only branch that spawned tasklist:

if (IS_WINDOWS) {
 const result = Bun.spawnSync(['tasklist', '/FI', `PID eq ${pid}`, '/NH', '/FO', 'CSV'], {...});
 return result.stdout.toString().includes(`"${pid}"`);
}

Every watchdog tick → a tasklist spawn → a console window. The parent watchdog two functions away already avoids exactly this by calling process.kill(pid, 0) directly; only isProcessAlive() took the spawn path.

Fix

Unify on signal-0 across all platforms. Node/Bun implement process.kill(pid, 0) on Windows via OpenProcess — a pure existence check, no child process, no window. The Windows-only branch (and its now-unused IS_WINDOWS const) are removed.

This also corrects a latent edge: the old branch collapsed every error to false, so a live-but-unsignalable process (EPERM) read as dead. Now ESRCH → dead, EPERM → alive.

export function isProcessAlive(pid: number): boolean {
 try {
 process.kill(pid, 0);
 return true;
 } catch (err: any) {
 // ESRCH → gone (false); EPERM → exists but not signallable → still alive.
 return err?.code === 'EPERM';
 }
}

The same isProcessAlive is compiled into the browse CLI binary's polling loops, so the one-file fix covers those on rebuild too. The watchdog's alive/dead branch is unchanged — signal-0 returns the same boolean it already keys on, so dead-agent detection and respawn still work.

Testing

bun test browse/test/error-handling.test.ts → 9/9 pass. Added:

• an EPERM-as-alive regression case (probes PID 1, which a non-root user can't signal), and
• a static tripwire asserting the isProcessAlive source never reintroduces tasklist/spawn — the idiomatic gstack guard for a Windows-only cosmetic bug that can't be exercised on macOS CI. Proven to fail on the old tasklist body before the fix.

The watchdog/terminal-agent suites (terminal-agent-watchdog.test.ts, watchdog.test.ts, etc.) stay green. One unrelated pre-existing failure in terminal-agent.test.ts (a source-guard grepping for spawnClaude(, since renamed to maybeSpawnPty) reproduces on clean main with this branch stashed — not touched here (this PR only changes browse/src/error-handling.ts + its test).

Fixes #1952