fix(browse): absorb #2414 residuals — EPERM-alive liveness + Windows-dead test tripwires (re-derived)

Re-derive of PR #2414 (SYKhayyat) onto current main. Most of the PR already
landed in earlier waves: the tick-derived RESPAWN_GUARD_WINDOW_MS, the
spawnTerminalAgent windowsHide flag, the process-liveness regression tests,
and the browse/test import.meta.path sweep are all on main. Two pieces
remained:

1. isProcessAlive EPERM semantics (error-handling.ts): on the signal-0 path,
   EPERM means the process EXISTS but we lack rights to signal it — that is
   ALIVE. Returning false made callers that validate liveness before killing
   (killAgentByRecord, the terminal-agent watchdog) skip the kill and respawn
   around a survivor — the self-reinforcing one-leak-per-tick chain from
   #2414/#2295. Matters for cross-user PID checks.

2. Six test/ files ADDED SINCE the PR reintroduced the exact Windows bug its
   second commit fixed: `new URL(import.meta.url).pathname` yields
   `/C:/Users/...` on Windows, so path.resolve prepends the cwd drive and
   every tripwire ENOENTs instead of asserting anything (egress-receipt,
   egress-lib, egress-receipt-wiring, gstack-egress-cli,
   pty-skill-seeding-wiring, skill-census). All six now use
   import.meta.path — Bun's absolute native path, identical arity.

The remaining #2414 piece — replacing the Windows tasklist probe with
signal-0 — lands as its own commit (#1952) on top of this shape.

Tests: the 6 touched test files 47 pass; process-liveness-windows +
error-handling 13 pass.

Re-derived from PR #2414 by @SYKhayyat. Fixes the residual of #2295.

Co-authored-by: SYKhayyat <shaulyoelkhayyat@gmail.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

browse/src/error-handling.ts

@@ -36,7 +36,15 @@ export function safeKill(pid: number, signal: NodeJS.Signals | number): void {
   }
 }
 
-/** Check if a PID is alive. Pure boolean probe — returns false for ALL errors. */
+/**
+ * Check if a PID is alive. Pure boolean probe — never throws.
+ *
+ * EPERM means the process EXISTS but we lack rights to signal it. That is
+ * alive — returning false there makes callers that validate liveness before
+ * killing (killAgentByRecord, the terminal-agent watchdog) skip the kill and
+ * respawn around a survivor, leaking one process per watchdog tick (#2414,
+ * #2295).
+ */
 export function isProcessAlive(pid: number): boolean {
   if (IS_WINDOWS) {
     try {
@@ -52,7 +60,7 @@ export function isProcessAlive(pid: number): boolean {
   try {
     process.kill(pid, 0);
     return true;
-  } catch {
-    return false;
+  } catch (err: any) {
+    return err?.code === 'EPERM';
   }
 }

test/egress-lib.test.ts

@@ -17,7 +17,7 @@ import * as os from 'os';
 import * as path from 'path';
 import { listReceipts, sha256Hex } from '../lib/egress-receipt';
 
-const ROOT = path.resolve(new URL(import.meta.url).pathname, '..', '..');
+const ROOT = path.resolve(import.meta.path, '..', '..');
 const LIB = path.join(ROOT, 'bin', 'gstack-egress-lib.sh');
 
 const received: string[] = [];

test/egress-receipt-wiring.test.ts

@@ -28,7 +28,7 @@ import { describe, test, expect } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
 
-const ROOT = path.resolve(new URL(import.meta.url).pathname, '..', '..');
+const ROOT = path.resolve(import.meta.path, '..', '..');
 
 function read(rel: string): string {
   return fs.readFileSync(path.join(ROOT, rel), 'utf-8');

test/egress-receipt.test.ts

@@ -31,7 +31,7 @@ import {
   writeReceipt,
 } from '../lib/egress-receipt';
 
-const ROOT = path.resolve(new URL(import.meta.url).pathname, '..', '..');
+const ROOT = path.resolve(import.meta.path, '..', '..');
 
 let home: string;
 

test/gstack-egress-cli.test.ts

@@ -19,7 +19,7 @@ import {
   writeReceipt,
 } from '../lib/egress-receipt';
 
-const ROOT = path.resolve(new URL(import.meta.url).pathname, '..', '..');
+const ROOT = path.resolve(import.meta.path, '..', '..');
 const BIN = path.join(ROOT, 'bin', 'gstack-egress');
 
 let home: string;

test/pty-skill-seeding-wiring.test.ts

@@ -17,7 +17,7 @@ import { describe, test, expect } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
 
-const ROOT = path.resolve(new URL(import.meta.url).pathname, '..', '..');
+const ROOT = path.resolve(import.meta.path, '..', '..');
 
 /** A PTY send whose payload starts with a slash command (`/name`, optionally
  * followed by `\r`, whitespace, or the closing quote). A second slash right

test/skill-census.test.ts

@@ -11,7 +11,7 @@ import * as fs from 'fs';
 import * as path from 'path';
 import { frontmatterName, skillCensus } from './helpers/skill-census';
 
-const ROOT = path.resolve(new URL(import.meta.url).pathname, '..', '..');
+const ROOT = path.resolve(import.meta.path, '..', '..');
 const census = skillCensus(ROOT);
 
 describe('skillCensus', () => {