fix(mcp): fix Windows MCP spawn double-quoting that breaks all MCP servers

The quoteWindowsShellArg function wrapped every argument in double quotes unconditionally, producing command strings like '"npx" "-y" "@playwright/mcp"'. When passed to spawn() with shell:true, Node.js wraps the entire string again for cmd.exe, causing double-quoting that breaks command parsing. All MCP servers (playwright, fetch, memory, github) failed to start on Windows. Fix: only quote arguments that contain spaces or double-quotes, leaving simple args unquoted.

Author: dengmik-commits

src/mcp/mcp-client.ts

@@ -425,9 +425,11 @@ export function createMcpSpawnSpec(
   if (platform === "win32") {
     return {
       // On Windows, shell: true lets cmd.exe resolve the command via PATHEXT
-      // (npx -> npx.cmd, etc.). Pass one quoted command line with no spawn
-      // args to avoid Node 24 DEP0190.
-      command: [command, ...args].map(quoteWindowsShellArg).join(" "),
+      // (npx -> npx.cmd, etc.). Join command and args into a single string
+      // with empty spawn args to avoid Node 24 DEP0190.
+      // Only quote arguments that contain spaces or double-quotes to prevent
+      // double-wrapping by Node.js's own shell quoting.
+      command: [command, ...args].map(quoteWindowsArgIfNeeded).join(" "),
       args: [],
       shell: true,
       windowsHide: true,
@@ -441,6 +443,9 @@ export function createMcpSpawnSpec(
   };
 }
 
-function quoteWindowsShellArg(arg: string): string {
-  return `"${arg.replace(/(\\*)"/g, '$1$1\\"').replace(/\\+$/g, "$&$&")}"`;
+function quoteWindowsArgIfNeeded(arg: string): string {
+  if (arg.includes(" ") || arg.includes('"')) {
+    return `"${arg.replace(/(\\*)"/g, '$1$1\\"').replace(/\\+$/g, "$&$&")}"`;
+  }
+  return arg;
 }

src/tests/mcp-client.test.ts

@@ -10,9 +10,9 @@ test("createMcpSpawnSpec keeps non-Windows MCP launches shell-free", () => {
   });
 });
 
-test("createMcpSpawnSpec avoids Windows shell args for Node 24", () => {
+test("createMcpSpawnSpec joins args without quoting when spaces are absent (Windows)", () => {
   assert.deepEqual(createMcpSpawnSpec("npx", ["-y", "@playwright/mcp@latest"], "win32"), {
-    command: '"npx" "-y" "@playwright/mcp@latest"',
+    command: "npx -y @playwright/mcp@latest",
     args: [],
     shell: true,
     windowsHide: true,