fix: skip remote URIs when resolving MCP server cwd

When the extension runs in the Local Extension Host on Windows while
connected to a remote workspace (SSH, Dev Container, etc.),
getWorkspaceDirs() returns vscode-remote:// URIs. These cannot be used
as a cwd for child_process.spawn(), causing "spawn cmd.exe ENOENT"
when starting MCP stdio servers.

Return undefined for non-file:// URIs so the spawn uses its default
cwd instead.

Fixes #10842

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: shanevcantwell

core/context/mcp/MCPConnection.ts

@@ -476,6 +476,13 @@ Org-level secrets can only be used for MCP by Background Agents (https://docs.co
         if (resolved.startsWith("file://")) {
           return fileURLToPath(resolved);
         }
+        // Remote URIs (e.g. vscode-remote://ssh-remote+host/path) cannot be
+        // used as a local cwd for child_process.spawn(). When the extension
+        // runs in the Local Extension Host on Windows while connected to a
+        // remote workspace, let the spawn use its default cwd instead.
+        if (resolved.includes("://")) {
+          return undefined;
+        }
         return resolved;
       }
       return resolved;

core/context/mcp/MCPConnection.vitest.ts

@@ -175,6 +175,16 @@ describe("MCPConnection", () => {
       );
       expect(mockResolve).toHaveBeenCalledWith("src", ide);
     });
+
+    it("should return undefined for remote URIs that cannot be used as local cwd", async () => {
+      const ide = {} as any;
+      vi.spyOn(ideUtils, "resolveRelativePathInDir").mockResolvedValue(
+        "vscode-remote://ssh-remote+192.168.137.2/home/user/project",
+      );
+      const conn = new MCPConnection(baseOptions, { ide });
+
+      await expect((conn as any).resolveCwd("src")).resolves.toBeUndefined();
+    });
   });
 
   describe("connectClient", () => {