fix(webui): keep the Mini App fixture's socket path inside the limit

A unix socket path has a hard limit — 104 bytes on macOS — and the Mini App's
owner socket sits four directories below the data directory. macOS's own
temporary directory is long enough that the socket path overflowed it, the bind
failed with `EINVAL`, and the run reported a Mini App that could not start
rather than the path that was too long. The fixture's data directory now goes
to the short temporary root. Windows names the endpoint with a pipe, so its
path does not matter there.

Author: stevenjj33

packages/webui/test/integration/miniapp-real-flow-support.ts

@@ -67,7 +67,13 @@ export async function closeAllBootedHosts(): Promise<void> {
 export async function bootRealHost(
   options: { readonly dev?: boolean; readonly serveBuiltClient?: boolean } = {},
 ): Promise<Booted> {
-  const dataDir = await mkdtemp(join(tmpdir(), "webui-miniapp-flow-"));
+  // The Mini App's owner socket sits four directories below the data
+  // directory, and a unix socket path has a hard limit — 104 bytes on macOS.
+  // macOS's own temporary directory is already long enough that the socket path
+  // overflows it, and the bind fails with `EINVAL`, so the fixture's data
+  // directory goes to the short temporary root instead. Windows names the
+  // endpoint with a pipe, so its path does not matter there.
+  const dataDir = await mkdtemp(join(process.platform === "win32" ? tmpdir() : "/tmp", "wmf-"));
   const workspaceDir = join(dataDir, "workspace");
   await mkdir(workspaceDir, { recursive: true });
   // A config file that already exists stops `ensureConfigFile()` from copying the