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/src/bun-polyfill.cjs

@@ -75,9 +75,11 @@ globalThis.Bun = {
       timeout: options.timeout,
       env: options.env,
       cwd: options.cwd,
-      // Bun never shows a console window; node's spawn defaults windowsHide to
-      // false, so without this every console child pops a window on Windows.
-      windowsHide: true,
+      // 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 — every console child pops a window.
+      // Forwarded (not hardcoded) so an explicit windowsHide:false survives.
+      windowsHide: options.windowsHide !== false,
     });
 
     return {
@@ -94,10 +96,12 @@ globalThis.Bun = {
       stdio,
       env: options.env,
       cwd: options.cwd,
-      // See spawnSync. This is the one users notice: spawnTerminalAgent() launches
-      // `bun run terminal-agent.ts` through here and the daemon respawns it on a
-      // watchdog, so an empty console window reappears every few minutes.
-      windowsHide: true,
+      // 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) popped a visible bun.exe window on every
+      // respawn until this was forwarded. Forwarded, not hardcoded, so an
+      // explicit windowsHide:false survives.
+      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;