fix: stream directly from chat-api, bypass Next.js proxy

Replaced the double-proxy (browser→Next.js→chat-api→Modal) with
direct streaming (browser→nginx→chat-api→Modal). Added nginx route
for /api/conversations → chat-api. Inlined SSE parsing in ChatWindow
instead of useSSE hook going through /api/chat/stream.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nginx/nginx.conf

@@ -32,6 +32,23 @@ http {
             proxy_set_header X-Forwarded-Proto $scheme;
         }
 
+        # Chat API — direct to backend for conversations + streaming
+        location /api/conversations {
+            limit_req zone=api burst=20 nodelay;
+            proxy_pass http://chat-api:8002/api/conversations;
+            proxy_set_header Host $host;
+            proxy_set_header X-Real-IP $remote_addr;
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            proxy_set_header X-Forwarded-Proto $scheme;
+
+            # SSE streaming support
+            proxy_buffering off;
+            proxy_cache off;
+            proxy_read_timeout 300s;
+            proxy_set_header Connection '';
+            chunked_transfer_encoding off;
+        }
+
         # Grafana (optional)
         location /grafana/ {
             proxy_pass http://grafana:3000/;

services/frontend/components/chat/ChatWindow.tsx

@@ -6,7 +6,6 @@ import MessageBubble from './MessageBubble';
 import EmptyState from './EmptyState';
 import ChatInput from './ChatInput';
 import { useChatStore } from '@/store/chatStore';
-import { useSSE } from '@/hooks/useSSE';
 import { useAuth } from '@/hooks/useAuth';
 import { authHeaders } from '@/lib/auth-client';
 import { parseSlashCommand } from '@/lib/slashCommands';
@@ -52,30 +51,89 @@ export default function ChatWindow() {
     scrollToBottom();
   }, [messages.length, streamingMsgId, scrollToBottom]);
 
-  const { start, stop, isStreaming } = useSSE('/api/chat/stream', {
-    onToken: (token) => {
-      streamingBufferRef.current += token;
-      if (streamingMsgId && currentConversationId) {
-        updateMessage(currentConversationId, streamingMsgId, streamingBufferRef.current);
+  const [isStreaming, setIsStreaming] = useState(false);
+  const abortRef = useRef<AbortController | null>(null);
+
+  const stop = useCallback(() => {
+    abortRef.current?.abort();
+    abortRef.current = null;
+    setIsStreaming(false);
+  }, []);
+
+  const streamFromApi = useCallback(async (convId: string, content: string, temp?: number, topk?: number) => {
+    stop();
+    const ac = new AbortController();
+    abortRef.current = ac;
+    setIsStreaming(true);
+
+    try {
+      const headers: Record<string, string> = {
+        'Content-Type': 'application/json',
+        ...authHeaders(),
+      };
+
+      // Call chat-api directly via nginx — no Next.js proxy
+      const res = await fetch(`/api/conversations/${convId}/messages`, {
+        method: 'POST',
+        headers,
+        body: JSON.stringify({ content, temperature: temp, max_tokens: 512, top_k: topk }),
+        signal: ac.signal,
+      });
+
+      if (!res.ok || !res.body) {
+        throw new Error(`HTTP ${res.status}`);
       }
-    },
-    onDone: () => {
+
+      const reader = res.body.getReader();
+      const decoder = new TextDecoder();
+      let buffer = '';
+
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done) break;
+
+        buffer += decoder.decode(value, { stream: true });
+        let nl: number;
+        while ((nl = buffer.indexOf('\n')) !== -1) {
+          const line = buffer.slice(0, nl).trim();
+          buffer = buffer.slice(nl + 1);
+          if (!line.startsWith('data:')) continue;
+          const payload = line.slice(5).trim();
+          if (!payload) continue;
+          try {
+            const data = JSON.parse(payload);
+            if (data.done) {
+              setStreamingMsgId(null);
+              streamingBufferRef.current = '';
+              setIsStreaming(false);
+              return;
+            }
+            if (typeof data.token === 'string') {
+              streamingBufferRef.current += data.token;
+              if (streamingMsgId && convId) {
+                updateMessage(convId, streamingMsgId!, streamingBufferRef.current);
+              }
+            }
+          } catch { /* skip malformed */ }
+        }
+      }
+
       setStreamingMsgId(null);
       streamingBufferRef.current = '';
-    },
-    onError: (err) => {
-      console.error('[chat] stream error:', err);
-      if (streamingMsgId && currentConversationId) {
-        updateMessage(
-          currentConversationId,
-          streamingMsgId,
-          `Error: ${err.message}. Using mock responses requires only the frontend; cloud streaming requires CHAT_API_URL.`,
-        );
+    } catch (err) {
+      if ((err as Error).name !== 'AbortError') {
+        console.error('[chat] stream error:', err);
+        if (streamingMsgId && currentConversationId) {
+          updateMessage(currentConversationId, streamingMsgId!, `Error: ${(err as Error).message}`);
+        }
       }
       setStreamingMsgId(null);
       streamingBufferRef.current = '';
-    },
-  });
+    } finally {
+      setIsStreaming(false);
+      abortRef.current = null;
+    }
+  }, [stop, streamingMsgId, currentConversationId, updateMessage]);
 
   const ensureConversation = useCallback(async () => {
     if (currentConversationId) return currentConversationId;
@@ -116,21 +174,7 @@ export default function ChatWindow() {
       setStreamingMsgId(assistantId);
       streamingBufferRef.current = '';
 
-      const history = [
-        ...(useChatStore.getState().conversations.find((c) => c.id === convId)?.messages ?? []),
-      ]
-        .filter((m) => m.role === 'user' || m.role === 'assistant')
-        .slice(0, -1)
-        .map((m) => ({ role: m.role, content: m.content }));
-
-      await start({
-        messages: history,
-        model,
-        temperature,
-        topK,
-        conversationId: convId,
-        auth: authHeaders(),
-      });
+      await streamFromApi(convId, text, temperature, topK);
     },
     [
       draft,
@@ -139,12 +183,12 @@ export default function ChatWindow() {
       temperature,
       topK,
       appendMessage,
-      model,
+      streamFromApi,
       setTemperature,
       setTopK,
       createConversation,
       newConversation,
-      start,
+      // streamFromApi in deps via earlier line
     ],
   );