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fix(mcp): fix Windows MCP spawn double-quoting that breaks all MCP servers #164

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fix(mcp): fix Windows MCP spawn double-quoting that breaks all MCP servers #164

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15 changes: 10 additions & 5 deletions src/mcp/mcp-client.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand All @@ -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;
}
4 changes: 2 additions & 2 deletions src/tests/mcp-client.test.ts
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Expand Up @@ -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,
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