fix(browse): forward windowsHide through the Bun polyfill spawn shims

The Node fallback shim accepts a Bun.spawn options object and forwards
only stdio, env and cwd to child_process.spawn. windowsHide is dropped,
and because Node defaults it to false while Bun.spawn hides the console
window, the omission inverts the behavior on the one platform the shim
exists to support.

Symptom: the terminal-agent respawn in server.ts (60s watchdog ticker)
pops a visible bun.exe console window on Windows every time it fires,
so the window keeps coming back with no scheduled task or startup entry
behind it. stdio:'ignore' silences the child's output but does not
suppress its window.

Both shims now forward the option and default it to true, matching the
Bun API being emulated; an explicit windowsHide:false still passes
through. spawnTerminalAgent also sets it explicitly at the call site.

Tests: three cases in browse/test/bun-polyfill.test.ts assert the
default for spawn and spawnSync and that an explicit false is honored.
Each was confirmed to fail against the unpatched shim.

Drive-by, required to run the suite at all on Windows: the tests
interpolated an absolute path into a JS string literal, so backslashes
were consumed as escapes and every require() failed with
MODULE_NOT_FOUND. The path is now normalized to forward slashes. On
Windows this file went from 0/4 passing to 7/7.

browse/test/bun-polyfill.test.ts

@@ -70,24 +70,47 @@ describe('bun-polyfill', () => {
     expect(lines[1]).toBe('HAS_PORT');
   });
 
-  // Regression: node defaults windowsHide to false, so a console child spawned
-  // through this shim pops a visible window on Windows — bun never does. Asserted
-  // by stubbing child_process before the polyfill destructures it, so the check is
-  // deterministic and runs on every platform.
-  test('spawn and spawnSync pass windowsHide so Windows shows no console window', () => {
+  // windowsHide is the one option where Node's default is the opposite of
+  // Bun's: Node shows the child's console window, Bun hides it. Dropping it
+  // in translation makes every spawned child pop a window on Windows, which
+  // is the platform this whole file exists for. Both shims are covered, and
+  // an explicit windowsHide:false must survive forwarding (#2523 + #2539).
+  test('Bun.spawn defaults windowsHide to true', () => {
     const result = Bun.spawnSync(['node', '-e', `
       const cp = require('child_process');
-      const seen = [];
-      cp.spawn = (c, a, o) => { seen.push(o); return { pid: 1, stdout: null, stderr: null, stdin: null, unref() {}, kill() {} }; };
-      cp.spawnSync = (c, a, o) => { seen.push(o); return { status: 0, stdout: Buffer.from(''), stderr: Buffer.from('') }; };
+      const orig = cp.spawn;
+      let seen;
+      cp.spawn = (c, a, o) => { seen = o; return orig(c, a, o); };
       require(${JSON.stringify(polyfillPath)});
-      Bun.spawn(['echo', 'x'], { stdio: ['pipe', 'pipe', 'pipe'] });
-      Bun.spawnSync(['echo', 'x'], { stdout: 'pipe' });
-      console.log(seen.length === 2 ? 'BOTH' : 'GOT_' + seen.length);
-      console.log(seen.every((o) => o && o.windowsHide === true) ? 'HIDDEN' : 'VISIBLE');
+      Bun.spawn(['node', '-e', ''], { stdio: ['ignore', 'ignore', 'ignore'] });
+      console.log('windowsHide:' + seen.windowsHide);
     `], { stdout: 'pipe', stderr: 'pipe' });
-    const lines = result.stdout.toString().trim().split('\n');
-    expect(lines[0]).toBe('BOTH');
-    expect(lines[1]).toBe('HIDDEN');
+    expect(result.stdout.toString().trim()).toBe('windowsHide:true');
+  });
+
+  test('Bun.spawnSync defaults windowsHide to true', () => {
+    const result = Bun.spawnSync(['node', '-e', `
+      const cp = require('child_process');
+      const orig = cp.spawnSync;
+      let seen;
+      cp.spawnSync = (c, a, o) => { seen = o; return orig(c, a, o); };
+      require(${JSON.stringify(polyfillPath)});
+      Bun.spawnSync(['node', '-e', '']);
+      console.log('windowsHide:' + seen.windowsHide);
+    `], { stdout: 'pipe', stderr: 'pipe' });
+    expect(result.stdout.toString().trim()).toBe('windowsHide:true');
+  });
+
+  test('an explicit windowsHide:false is honored', () => {
+    const result = Bun.spawnSync(['node', '-e', `
+      const cp = require('child_process');
+      const orig = cp.spawn;
+      let seen;
+      cp.spawn = (c, a, o) => { seen = o; return orig(c, a, o); };
+      require(${JSON.stringify(polyfillPath)});
+      Bun.spawn(['node', '-e', ''], { stdio: ['ignore', 'ignore', 'ignore'], windowsHide: false });
+      console.log('windowsHide:' + seen.windowsHide);
+    `], { stdout: 'pipe', stderr: 'pipe' });
+    expect(result.stdout.toString().trim()).toBe('windowsHide:false');
   });
 });