fix: address additional code review feedback

- Add path.normalize() for Windows mixed separator handling
- Add validation to check Node executable exists after finding it
- Improve error dialog with specific troubleshooting advice for Node.js
  related errors vs general errors
- Include source info in validation error message

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/main.ts

@@ -134,6 +134,12 @@ async function startServer(): Promise<void> {
     logger: (msg) => console.log(`[Electron] ${msg}`),
   });
   const command = nodeResult.nodePath;
+
+  // Validate that the found Node executable actually exists
+  if (command !== 'node' && !fs.existsSync(command)) {
+    throw new Error(`Node.js executable not found at: ${command} (source: ${nodeResult.source})`);
+  }
+
   let args: string[];
   let serverPath: string;
 
@@ -338,9 +344,15 @@ app.whenReady().then(async () => {
     createWindow();
   } catch (error) {
     console.error('[Electron] Failed to start:', error);
+    const errorMessage = (error as Error).message;
+    const isNodeError = errorMessage.includes('Node.js');
     dialog.showErrorBox(
       'Automaker Failed to Start',
-      `The application failed to start.\n\n${(error as Error).message}\n\nPlease ensure Node.js is installed and accessible.`
+      `The application failed to start.\n\n${errorMessage}\n\n${
+        isNodeError
+          ? 'Please install Node.js from https://nodejs.org or via a package manager (Homebrew, nvm, fnm).'
+          : 'Please check the application logs for more details.'
+      }`
     );
     app.quit();
   }

libs/platform/src/node-finder.ts

@@ -334,8 +334,10 @@ export function buildEnhancedPath(nodePath: string, currentPath: string = ''): s
 
   // Don't add if already present or if it's just '.'
   // Use path segment matching to avoid false positives (e.g., /opt/node vs /opt/node-v18)
-  const pathSegments = currentPath.split(path.delimiter);
-  if (nodeDir === '.' || pathSegments.includes(nodeDir)) {
+  // Normalize paths for comparison to handle mixed separators on Windows
+  const normalizedNodeDir = path.normalize(nodeDir);
+  const pathSegments = currentPath.split(path.delimiter).map((s) => path.normalize(s));
+  if (normalizedNodeDir === '.' || pathSegments.includes(normalizedNodeDir)) {
     return currentPath;
   }