fix(windows): forward windowsHide through the bun-polyfill spawn shims

windowsHide is the one spawn option where Node's default is the opposite
of Bun's: Node shows the child's console window, Bun.spawn hides it.
The polyfill's spawn and spawnSync shims dropped the option entirely, so
the Node fallback path (dist/bun-polyfill.cjs) silently inverted the
behavior on the one platform the shim exists to serve — every watchdog
respawn of the terminal agent popped a visible bun.exe console window.

Three sites fixed:
- Bun.spawnSync shim: forwards windowsHide with Bun-matching default true
- Bun.spawn shim: same (stdio:'ignore' silences output but does NOT
  suppress the console window on Windows)
- spawnTerminalAgent in terminal-agent-control.ts: explicit
  windowsHide: true, so the Node fallback path behaves like Bun-native

An explicit windowsHide: false is honored at both shims. Three focused
tests pin the default-true, default-true-sync, and explicit-false paths
by intercepting child_process in a subprocess; the test file's require
path now uses forward slashes so it survives interpolation into a JS
string literal on Windows.

Supersedes PRs #2523, #2294 and #2290, which each covered a subset of
these sites.

Contributed by @jerrynicholsai (PR #2539); earlier fixes by @jwilk-hrep, @rroojrooj and @WimvandenHeijkant covered subsets of the same sites.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

browse/src/bun-polyfill.cjs

@@ -75,6 +75,10 @@ globalThis.Bun = {
       timeout: options.timeout,
       env: options.env,
       cwd: options.cwd,
+      // Node defaults windowsHide to false; Bun.spawn hides the console
+      // window. Without this the shim silently inverts the behavior on the
+      // one platform it exists to serve. See the spawn() note below.
+      windowsHide: options.windowsHide !== false,
     });
 
     return {
@@ -91,6 +95,11 @@ globalThis.Bun = {
       stdio,
       env: options.env,
       cwd: options.cwd,
+      // stdio:'ignore' silences a child's output but does not suppress its
+      // console window on Windows. The terminal-agent respawn (server.ts
+      // watchdog, 60s ticker) therefore popped a visible bun.exe window on
+      // every respawn until this was forwarded.
+      windowsHide: options.windowsHide !== false,
     });
 
     return {

browse/src/terminal-agent-control.ts

@@ -77,6 +77,10 @@ export function spawnTerminalAgent(opts: {
       ...(opts.extraEnv || {}),
     },
     stdio: ['ignore', 'ignore', 'ignore'],
+    // Explicit for the Node fallback path (dist/bun-polyfill.cjs), where the
+    // host default is the opposite of Bun's. A visible console window on every
+    // watchdog respawn is the symptom when this is missing.
+    windowsHide: true,
   });
   proc.unref?.();
   return proc.pid ?? null;