fix: detect Windows shell from environment

src/helpers/os-detect.ts

@@ -2,13 +2,54 @@ import os from 'os';
 import path from 'path';
 import i18n from './i18n';
 
+function trimExecutableExtension(shell: string) {
+  return shell.replace(/\.(exe|cmd)$/i, '').toLowerCase();
+}
+
+function shellNameFromPath(shellPath: string) {
+  return trimExecutableExtension(
+    path.win32.basename(shellPath) || path.posix.basename(shellPath)
+  );
+}
+
+function normalizeWindowsShell(shellName: string) {
+  if (shellName === 'pwsh' || shellName === 'powershell') {
+    return 'powershell';
+  }
+
+  if (shellName === 'cmd') {
+    return 'cmd';
+  }
+
+  if (shellName === 'bash' || shellName === 'zsh' || shellName === 'fish') {
+    return shellName;
+  }
+}
+
+function detectWindowsShell(env: NodeJS.ProcessEnv) {
+  const shellFromEnv = env.SHELL
+    ? normalizeWindowsShell(shellNameFromPath(env.SHELL))
+    : undefined;
+  if (shellFromEnv) {
+    return shellFromEnv;
+  }
+
+  const comSpecShell = env.ComSpec
+    ? normalizeWindowsShell(shellNameFromPath(env.ComSpec))
+    : undefined;
+  if (comSpecShell) {
+    return comSpecShell;
+  }
+
+  return 'powershell';
+}
+
 export function detectShell() {
   try {
-    // Detect if we're running on win32 and assume powershell
     if (os.platform() === 'win32') {
-      return 'powershell';
+      return detectWindowsShell(process.env);
     }
-    // otherwise return current shell; default to bash
+
     return path.basename(os.userInfo().shell ?? 'bash');
   } catch (err: unknown) {
     if (err instanceof Error) {