feat: Upgrade chat to Gemini Pro with configurable model

- Update Google AI model to gemini-pro-latest via env var
- Add GOOGLE_AI_MODEL environment variable for easy model switching
- Add initial greeting message explaining Ponderants features
- Re-add tool call handling to display node suggestions
- Fix chat authentication and streaming responses

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

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

app/api/chat/route.ts

@@ -4,14 +4,21 @@ import { cookies } from 'next/headers';
 import { NodeSuggestionSchema } from '@/lib/ai-schemas';
 import { z } from 'zod';
 
-export const runtime = 'edge';
+// Edge runtime removed - cookies() requires Node.js runtime
+export const maxDuration = 30;
 
 export async function POST(req: Request) {
   // Check authentication
   const cookieStore = await cookies();
   const authCookie = cookieStore.get('ponderants-auth');
 
+  console.log('[Chat API] Cookie check:', {
+    hasCookie: !!authCookie,
+    allCookies: cookieStore.getAll().map(c => c.name),
+  });
+
   if (!authCookie) {
+    console.log('[Chat API] No auth cookie found, returning 401');
     return new Response('Unauthorized', { status: 401 });
   }
 
@@ -32,9 +39,16 @@ to propose it as a new "thought node". Do not suggest a node until the
 idea is fully formed.
 For all other conversation, just respond as a helpful AI.`;
 
+  // Get model from environment variable
+  const modelName = process.env.GOOGLE_AI_MODEL;
+  if (!modelName) {
+    console.error('[Chat API] GOOGLE_AI_MODEL environment variable is not set');
+    return new Response('Server configuration error', { status: 500 });
+  }
+
   // Use the Vercel AI SDK's streamText function with tools
   const result = streamText({
-    model: google('gemini-1.5-flash'),
+    model: google(modelName),
     system: systemPrompt,
     messages: convertToModelMessages(messages),
 

app/chat/page.tsx

@@ -21,13 +21,32 @@ export default function ChatPage() {
   const viewport = useRef<HTMLDivElement>(null);
   const [input, setInput] = useState('');
 
-  const { messages, sendMessage, isLoading } = useChat({
+  const { messages, sendMessage, isLoading, setMessages } = useChat({
     api: '/api/chat',
     body: {
       persona: 'Socratic',
     },
+    credentials: 'include',
   });
 
+  // Add initial greeting message on first load
+  useEffect(() => {
+    if (messages.length === 0) {
+      setMessages([
+        {
+          id: 'initial-greeting',
+          role: 'assistant',
+          parts: [
+            {
+              type: 'text',
+              text: 'Welcome to Ponderants! I\'m here to help you explore and structure your ideas through conversation.\n\nWhat would you like to talk about today? I can adapt my interview style to best suit your needs (Socratic questioning, collaborative brainstorming, or other approaches).\n\nJust start sharing your thoughts, and we\'ll discover meaningful insights together.',
+            },
+          ],
+        },
+      ]);
+    }
+  }, []);
+
   // Auto-scroll to bottom
   useEffect(() => {
     viewport.current?.scrollTo({
@@ -79,6 +98,31 @@ export default function ChatPage() {
                     </Text>
                   );
                 }
+
+                // Handle tool calls (e.g., suggest_node)
+                if (part.type === 'tool-call') {
+                  return (
+                    <Paper key={i} withBorder p="xs" mt="xs" bg="dark.6">
+                      <Text size="xs" c="dimmed" mb="xs">
+                        💡 Node Suggestion
+                      </Text>
+                      <Text fw={600}>{part.args.title}</Text>
+                      <Text size="sm" mt="xs">
+                        {part.args.content}
+                      </Text>
+                      {part.args.tags && part.args.tags.length > 0 && (
+                        <Group gap="xs" mt="xs">
+                          {part.args.tags.map((tag: string, tagIdx: number) => (
+                            <Text key={tagIdx} size="xs" c="blue.4">
+                              #{tag}
+                            </Text>
+                          ))}
+                        </Group>
+                      )}
+                    </Paper>
+                  );
+                }
+
                 return null;
               })}
             </Paper>