feat(chat): add guest chat mode for unauthenticated users

- Add POST /api/chat/guest endpoint (no auth required)
- Add proxyGuestChat() method using configurable LLM endpoint
- Add streamGuestChat() function to frontend chat API
- Modify useChat to fall back to guest mode on auth errors (403/401)
- Remove !user check from ChatInput disabled prop
- Configure guest LLM via env vars: GUEST_LLM_URL, GUEST_LLM_API_KEY, GUEST_LLM_MODEL
- Default guest LLM: http://10.1.1.42:11434/v1 (Ollama) with llama3.2 model

apps/web/src/components/chat/Chat.tsx

@@ -352,7 +352,7 @@ export const Chat = forwardRef<ChatRef, ChatProps>(function Chat(
         <div className="mx-auto max-w-4xl px-4 py-4 lg:px-8">
           <ChatInput
             onSend={handleSendMessage}
-            disabled={isChatLoading || !user}
+            disabled={isChatLoading}
             inputRef={inputRef}
             isStreaming={isStreaming}
             onStopStreaming={abortStream}

apps/web/src/hooks/useChat.ts

@@ -7,6 +7,7 @@ import { useState, useCallback, useRef } from "react";
 import {
   sendChatMessage,
   streamChatMessage,
+  streamGuestChat,
   type ChatMessage as ApiChatMessage,
 } from "@/lib/api/chat";
 import { createConversation, updateConversation, getIdea, type Idea } from "@/lib/api/ideas";
@@ -278,10 +279,69 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
           return;
         }
 
-        // Streaming failed — fall back to non-streaming
-        console.warn("Streaming failed, falling back to non-streaming", {
-          error: err instanceof Error ? err : new Error(String(err)),
-        });
+        // Streaming failed - check if auth error, try guest mode
+        const isAuthError = err instanceof Error && 
+          (err.message.includes("403") || err.message.includes("401") || 
+           err.message.includes("auth") || err.message.includes("Forbidden"));
+
+        if (isAuthError) {
+          console.warn("Auth failed, trying guest chat mode");
+          
+          // Try guest chat streaming
+          try {
+            await new Promise<void>((guestResolve, guestReject) => {
+              let hasReceivedData = false;
+
+              streamGuestChat(
+                request,
+                (chunk: string) => {
+                  if (!hasReceivedData) {
+                    hasReceivedData = true;
+                    setIsLoading(false);
+                    setIsStreaming(true);
+                    setMessages((prev) => {
+                      const updated = [...prev, { ...placeholderMessage }];
+                      messagesRef.current = updated;
+                      return updated;
+                    });
+                  }
+
+                  setMessages((prev) => {
+                    const updated = prev.map((msg) =>
+                      msg.id === assistantMessageId ? { ...msg, content: msg.content + chunk } : msg
+                    );
+                    messagesRef.current = updated;
+                    return updated;
+                  });
+                },
+                () => {
+                  streamingSucceeded = true;
+                  setIsStreaming(false);
+                  guestResolve();
+                },
+                (guestErr: Error) => {
+                  guestReject(guestErr);
+                },
+                controller.signal
+              );
+            });
+          } catch (guestErr: unknown) {
+            // Guest also failed
+            setMessages((prev) => {
+              const withoutPlaceholder = prev.filter((m) => m.id !== assistantMessageId);
+              messagesRef.current = withoutPlaceholder;
+              return withoutPlaceholder;
+            });
+            const errorMsg = guestErr instanceof Error ? guestErr.message : "Chat unavailable";
+            setError(`Unable to connect to chat: ${errorMsg}`);
+            setIsLoading(false);
+            return;
+          }
+        } else {
+          // Streaming failed — fall back to non-streaming
+          console.warn("Streaming failed, falling back to non-streaming", {
+            error: err instanceof Error ? err : new Error(String(err)),
+          });
 
         setMessages((prev) => {
           const withoutPlaceholder = prev.filter((m) => m.id !== assistantMessageId);

apps/web/src/lib/api/chat.ts

@@ -92,6 +92,141 @@ async function ensureCsrfTokenForStream(): Promise<string> {
   return fetchCsrfToken();
 }
 
+/**
+ * Stream a guest chat message (no authentication required).
+ * Uses /api/chat/guest endpoint with shared LLM configuration.
+ *
+ * @param request - Chat request
+ * @param onChunk - Called with each token string as it arrives
+ * @param onComplete - Called when the stream finishes successfully
+ * @param onError - Called if the stream encounters an error
+ * @param signal - Optional AbortSignal for cancellation
+ */
+export function streamGuestChat(
+  request: ChatRequest,
+  onChunk: (chunk: string) => void,
+  onComplete: () => void,
+  onError: (error: Error) => void,
+  signal?: AbortSignal
+): void {
+  void (async (): Promise<void> => {
+    try {
+      const response = await fetch(`${API_BASE_URL}/api/chat/guest`, {
+        method: "POST",
+        headers: {
+          "Content-Type": "application/json",
+        },
+        credentials: "include",
+        body: JSON.stringify({ messages: request.messages, stream: true }),
+        signal: signal ?? null,
+      });
+
+      if (!response.ok) {
+        const errorText = await response.text().catch(() => response.statusText);
+        throw new Error(`Guest chat failed: ${errorText}`);
+      }
+
+      if (!response.body) {
+        throw new Error("Response body is not readable");
+      }
+
+      const reader = response.body.getReader();
+      const decoder = new TextDecoder("utf-8");
+      let buffer = "";
+
+      let readerDone = false;
+      while (!readerDone) {
+        const { done, value } = await reader.read();
+        readerDone = done;
+        if (done) {
+          break;
+        }
+
+        buffer += decoder.decode(value, { stream: true });
+
+        // SSE messages are separated by double newlines
+        const parts = buffer.split("\n\n");
+        buffer = parts.pop() ?? "";
+
+        for (const part of parts) {
+          const trimmed = part.trim();
+          if (!trimmed) continue;
+
+          // Handle event: error format
+          const eventMatch = /^event:\s*(\S+)\n/i.exec(trimmed);
+          const dataMatch = /^data:\s*(.+)$/im.exec(trimmed);
+
+          if (eventMatch?.[1] === "error" && dataMatch?.[1]) {
+            try {
+              const errorData = JSON.parse(dataMatch[1].trim()) as {
+                error?: string;
+              };
+              throw new Error(errorData.error ?? "Stream error occurred");
+            } catch (parseErr) {
+              if (parseErr instanceof SyntaxError) {
+                throw new Error("Stream error occurred");
+              }
+              throw parseErr;
+            }
+          }
+
+          // Standard SSE format: data: {...}
+          for (const line of trimmed.split("\n")) {
+            if (!line.startsWith("data: ")) continue;
+
+            const data = line.slice("data: ".length).trim();
+
+            if (data === "[DONE]") {
+              onComplete();
+              return;
+            }
+
+            try {
+              const parsed: unknown = JSON.parse(data);
+
+              // Handle OpenAI format
+              const openAiChunk = parsed as OpenAiSseChunk;
+              if (openAiChunk.choices?.[0]?.delta?.content) {
+                onChunk(openAiChunk.choices[0].delta.content);
+                continue;
+              }
+
+              // Handle simple token format
+              const simpleChunk = parsed as SimpleTokenChunk;
+              if (simpleChunk.token) {
+                onChunk(simpleChunk.token);
+                continue;
+              }
+
+              if (simpleChunk.done === true) {
+                onComplete();
+                return;
+              }
+
+              const error = openAiChunk.error ?? simpleChunk.error;
+              if (error) {
+                throw new Error(error);
+              }
+            } catch (parseErr) {
+              if (parseErr instanceof SyntaxError) {
+                continue;
+              }
+              throw parseErr;
+            }
+          }
+        }
+      }
+
+      onComplete();
+    } catch (err: unknown) {
+      if (err instanceof DOMException && err.name === "AbortError") {
+        return;
+      }
+      onError(err instanceof Error ? err : new Error(String(err)));
+    }
+  })();
+}
+
 /**
  * Stream a chat message from the LLM using SSE over fetch.
  *