fix(windows): quote command paths with spaces when spawning with shell

shell: true passes commands to cmd.exe /d /s /c which strips outer
quotes, causing paths like C:\Program Files\... to split at the space.

packages/server/src/server/agent/provider-launch-config.test.ts

@@ -1,7 +1,8 @@
-import { beforeEach, describe, expect, test, vi } from "vitest";
+import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
 
 import {
   findExecutable,
+  quoteWindowsCommand,
   resolveProviderCommandPrefix,
   applyProviderEnv,
   type ProviderRuntimeSettings,
@@ -218,3 +219,39 @@ describe("findExecutable", () => {
     expect(findExecutableDependencies.existsSync).toHaveBeenCalledWith("/usr/local/bin/codex");
   });
 });
+
+describe("quoteWindowsCommand", () => {
+  const originalPlatform = process.platform;
+
+  function setPlatform(value: string) {
+    Object.defineProperty(process, "platform", { value, writable: true });
+  }
+
+  afterEach(() => {
+    setPlatform(originalPlatform);
+  });
+
+  test("quotes a Windows path with spaces", () => {
+    setPlatform("win32");
+    expect(quoteWindowsCommand("C:\\Program Files\\Anthropic\\claude.exe")).toBe(
+      '"C:\\Program Files\\Anthropic\\claude.exe"',
+    );
+  });
+
+  test("does not double-quote an already-quoted path", () => {
+    setPlatform("win32");
+    expect(quoteWindowsCommand('"C:\\Program Files\\Anthropic\\claude.exe"')).toBe(
+      '"C:\\Program Files\\Anthropic\\claude.exe"',
+    );
+  });
+
+  test("returns the command unchanged when there are no spaces", () => {
+    setPlatform("win32");
+    expect(quoteWindowsCommand("C:\\nvm4w\\nodejs\\codex")).toBe("C:\\nvm4w\\nodejs\\codex");
+  });
+
+  test("returns the command unchanged on non-Windows platforms", () => {
+    setPlatform("darwin");
+    expect(quoteWindowsCommand("/usr/local/bin/claude code")).toBe("/usr/local/bin/claude code");
+  });
+});