Validate Mosh client is executable in Settings UI

Address Codex P2 on PR #849 commit b6c384af. UI's debounced validator
called validatePath which only reported exists / isFile / isDirectory,
so a regular file without the POSIX execute bit (e.g. a stray
/etc/hosts-style path) was marked as valid in Settings — but
startMoshSession's isExecutableFile check then rejected the same path
at connect time, deferring the error until the user actually tried to
use Mosh.

- validatePath now returns `isExecutable: boolean`, mirroring
  isExecutableFile semantics (POSIX: stat.mode & 0o111; Win32: any
  regular file is treated as executable since NTFS lacks POSIX bits).
  Existing callers (localShell, localStartDir) ignore the new field.
- global.d.ts ValidatePath return type extended.
- SettingsTerminalTab Mosh validator surfaces a `notExecutable`
  message when the file exists but lacks exec permissions, keeping
  the UI in lockstep with main-process gating.
- en / zh-CN strings for the new state.

Verified: /bin/sh -> isExecutable:true, /etc/hosts -> false, /etc ->
false (directory). UI now warns immediately on the regression case.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

application/i18n/locales/en.ts

@@ -383,6 +383,7 @@ const en: Messages = {
   'settings.terminal.mosh.client.placeholder': 'Auto-detect',
   'settings.terminal.mosh.client.notFound': 'File not found at that path.',
   'settings.terminal.mosh.client.isDirectory': 'Path points to a directory, not an executable.',
+  'settings.terminal.mosh.client.notExecutable': 'File exists but is not executable. Run `chmod +x` on it or pick another binary.',
   'settings.terminal.mosh.detect': 'Detect',
   'settings.terminal.mosh.browse': 'Browse…',
   'settings.terminal.mosh.detected': 'Detected at',

application/i18n/locales/zh-CN.ts

@@ -1467,6 +1467,7 @@ const zhCN: Messages = {
   'settings.terminal.mosh.client.placeholder': '自动探测',
   'settings.terminal.mosh.client.notFound': '该路径下未找到文件。',
   'settings.terminal.mosh.client.isDirectory': '该路径指向目录而非可执行文件。',
+  'settings.terminal.mosh.client.notExecutable': '文件存在但不可执行。请对其执行 `chmod +x`，或选择其它二进制文件。',
   'settings.terminal.mosh.detect': '探测',
   'settings.terminal.mosh.browse': '浏览…',
   'settings.terminal.mosh.detected': '已找到',

components/settings/tabs/SettingsTerminalTab.tsx

@@ -478,7 +478,11 @@ export default function SettingsTerminalTab(props: {
     }
     const timeoutId = setTimeout(() => {
       bridge.validatePath(moshPath, "file").then((result) => {
-        if (result.exists && result.isFile) {
+        if (result.exists && result.isFile && !result.isExecutable) {
+          // Stays consistent with startMoshSession's isExecutableFile check —
+          // a regular file without the execute bit can't actually launch.
+          setMoshValidation({ valid: false, message: t("settings.terminal.mosh.client.notExecutable") });
+        } else if (result.exists && result.isFile) {
           setMoshValidation({ valid: true });
         } else if (result.exists && result.isDirectory) {
           setMoshValidation({ valid: false, message: t("settings.terminal.mosh.client.isDirectory") });

electron/bridges/terminalBridge.cjs

@@ -1287,29 +1287,42 @@ function getDefaultShell() {
  * Validate a path - check if it exists and whether it's a file or directory
  * @param {object} event - IPC event
  * @param {object} payload - Contains { path: string, type?: 'file' | 'directory' | 'any' }
- * @returns {{ exists: boolean, isFile: boolean, isDirectory: boolean }}
+ * @returns {{ exists: boolean, isFile: boolean, isDirectory: boolean, isExecutable: boolean }}
+ *
+ * `isExecutable` mirrors isExecutableFile(): POSIX requires the file mode
+ * to have an execute bit; Win32 treats any regular file as executable
+ * (NTFS lacks POSIX bits — extension/PATHEXT decides at spawn time).
+ * Existing callers ignore the new field; consumers that need exec
+ * semantics (e.g. Mosh client path) read it explicitly.
  */
+function statIsExecutable(stat) {
+  if (!stat || !stat.isFile()) return false;
+  if (process.platform === "win32") return true;
+  return (stat.mode & 0o111) !== 0;
+}
+
 function validatePath(event, payload) {
   const targetPath = payload?.path;
   const type = payload?.type || 'any';
   if (!targetPath) {
-    return { exists: false, isFile: false, isDirectory: false };
+    return { exists: false, isFile: false, isDirectory: false, isExecutable: false };
   }
-  
+
   try {
     // Resolve path (handle ~, etc.)
     let resolvedPath = expandHomePath(targetPath);
     resolvedPath = path.resolve(resolvedPath);
-    
+
     if (fs.existsSync(resolvedPath)) {
       const stat = fs.statSync(resolvedPath);
       return {
         exists: true,
         isFile: stat.isFile(),
         isDirectory: stat.isDirectory(),
+        isExecutable: statIsExecutable(stat),
       };
     }
-    
+
     // If type is 'file' and path doesn't exist, try to resolve via PATH (for executables like cmd.exe, powershell.exe)
     if (type === 'file') {
       const resolvedExecutable = findExecutable(targetPath);
@@ -1320,6 +1333,7 @@ function validatePath(event, payload) {
           exists: true,
           isFile: stat.isFile(),
           isDirectory: stat.isDirectory(),
+          isExecutable: statIsExecutable(stat),
         };
       }
       // Also try with .exe extension on Windows if not already present
@@ -1331,15 +1345,16 @@ function validatePath(event, payload) {
             exists: true,
             isFile: stat.isFile(),
             isDirectory: stat.isDirectory(),
+            isExecutable: statIsExecutable(stat),
           };
         }
       }
     }
-    
-    return { exists: false, isFile: false, isDirectory: false };
+
+    return { exists: false, isFile: false, isDirectory: false, isExecutable: false };
   } catch (err) {
     console.warn(`[Terminal] Error validating path "${targetPath}":`, err.message);
-    return { exists: false, isFile: false, isDirectory: false };
+    return { exists: false, isFile: false, isDirectory: false, isExecutable: false };
   }
 }
 

global.d.ts

@@ -216,7 +216,7 @@ declare global {
     }>>;
     getDefaultShell?(): Promise<string>;
     discoverShells?(): Promise<DiscoveredShell[]>;
-    validatePath?(path: string, type?: 'file' | 'directory' | 'any'): Promise<{ exists: boolean; isFile: boolean; isDirectory: boolean }>;
+    validatePath?(path: string, type?: 'file' | 'directory' | 'any'): Promise<{ exists: boolean; isFile: boolean; isDirectory: boolean; isExecutable: boolean }>;
     generateKeyPair?(options: {
       type: 'RSA' | 'ECDSA' | 'ED25519';
       bits?: number;