Fix Windows default shell for terminal creation

packages/server/src/terminal/terminal.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect, afterEach } from "vitest";
 import {
   createTerminal,
   ensureNodePtySpawnHelperExecutableForCurrentPlatform,
+  resolveDefaultTerminalShell,
   type TerminalSession,
 } from "./terminal.js";
 import { chmodSync, mkdtempSync, mkdirSync, rmSync, statSync, writeFileSync } from "node:fs";
@@ -111,6 +112,18 @@ describe("Terminal", () => {
       expect(statSync(helperPath).mode & 0o111).toBe(0o111);
     });
 
+    it("uses cmd.exe-compatible default shell on Windows", () => {
+      expect(resolveDefaultTerminalShell({ platform: "win32", env: {} })).toBe(
+        "C:\\Windows\\System32\\cmd.exe",
+      );
+      expect(
+        resolveDefaultTerminalShell({
+          platform: "win32",
+          env: { ComSpec: "C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe" },
+        }),
+      ).toBe("C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe");
+    });
+
     it("creates a terminal session with an id, name, and cwd", async () => {
       const session = trackSession(
         await createTerminal({

packages/server/src/terminal/terminal.ts

@@ -119,6 +119,22 @@ export function ensureNodePtySpawnHelperExecutableForCurrentPlatform(
   }
 }
 
+export function resolveDefaultTerminalShell(
+  options: {
+    platform?: NodeJS.Platform;
+    env?: NodeJS.ProcessEnv;
+  } = {},
+): string {
+  const platform = options.platform ?? process.platform;
+  const env = options.env ?? process.env;
+
+  if (platform === "win32") {
+    return env.ComSpec || env.COMSPEC || "C:\\Windows\\System32\\cmd.exe";
+  }
+
+  return env.SHELL || "/bin/sh";
+}
+
 function extractCell(terminal: TerminalType, row: number, col: number): TerminalCell {
   const buffer = terminal.buffer.active;
   const line = buffer.getLine(row);
@@ -299,12 +315,13 @@ export function captureTerminalLines(
 export async function createTerminal(options: CreateTerminalOptions): Promise<TerminalSession> {
   const {
     cwd,
-    shell = process.env.SHELL || "/bin/sh",
+    shell,
     env = {},
     rows = 24,
     cols = 80,
     name = "Terminal",
   } = options;
+  const resolvedShell = shell ?? resolveDefaultTerminalShell();
 
   const id = randomUUID();
   const listeners = new Set<(msg: ServerMessage) => void>();
@@ -324,7 +341,7 @@ export async function createTerminal(options: CreateTerminalOptions): Promise<Te
   ensureNodePtySpawnHelperExecutableForCurrentPlatform();
 
   // Create PTY
-  const ptyProcess = pty.spawn(shell, [], {
+  const ptyProcess = pty.spawn(resolvedShell, [], {
     name: "xterm-256color",
     cols,
     rows,