feat: multiple named conversations for the cooking assistant

The general assistant had exactly one conversation per user forever
(recipeId null on chat_messages) — no way to start fresh or organize
by topic. Adds an ai_conversations table (title, timestamps) and a
nullable conversationId FK on chat_messages; the assistant panel gets
a conversations menu to create/switch/rename/delete, auto-titling a
new conversation from its first question.

Per-recipe chat is untouched — each recipe already has one natural
thread, so multi-conversation support only applies to the homepage
assistant. Pre-existing general messages (no conversationId) aren't
migrated into the new model and won't appear in the conversation list.

Requires migration 0042 to run against a live DB — not applied in
this sandbox (no Docker here); run `pnpm db:migrate`.

v0.43.0

apps/web/components/recipe/cooking-assistant-panel.tsx

@@ -9,7 +9,7 @@ import { MessageCircle, Send, Bot, User, Maximize2, Minimize2 } from "lucide-rea
 import ReactMarkdown from "react-markdown";
 import { cn } from "@/lib/utils";
 import { ChatHistorySearch } from "./chat-history-search";
-import { ClearChatHistoryButton } from "./clear-chat-history-button";
+import { ConversationMenu, type Conversation } from "./conversation-menu";
 
 type Message = {
   role: "user" | "assistant";
@@ -26,18 +26,59 @@ export function CookingAssistantPanel() {
   const [messages, setMessages] = useState<Message[]>([]);
   const [input, setInput] = useState("");
   const [loading, setLoading] = useState(false);
+  const [conversationId, setConversationId] = useState<string | null>(null);
   const bottomRef = useRef<HTMLDivElement>(null);
   const historyLoadedRef = useRef(false);
 
+  async function loadMessages(id: string) {
+    try {
+      const res = await fetch(`/api/v1/ai/chat-history?conversationId=${id}&limit=50`);
+      const json = res.ok ? (await res.json()) as { data?: HistoryEntry[] } : null;
+      setMessages(json?.data?.length ? json.data.map((m) => ({ role: m.role, content: m.content })) : []);
+    } catch {
+      setMessages([]);
+    }
+  }
+
+  function handleSelectConversation(id: string) {
+    setConversationId(id);
+    void loadMessages(id);
+  }
+
+  function handleConversationCreated(conversation: Conversation) {
+    setConversationId(conversation.id);
+    setMessages([]);
+  }
+
+  function handleActiveConversationDeleted() {
+    // Fall back to a fresh conversation rather than leaving the panel
+    // pointed at an id that no longer exists.
+    fetch("/api/v1/ai/conversations", { method: "POST" })
+      .then((res) => (res.ok ? res.json() : null))
+      .then((created: Conversation | null) => {
+        if (created) {
+          setConversationId(created.id);
+          setMessages([]);
+        }
+      })
+      .catch(() => {});
+  }
+
   useEffect(() => {
     if (!open || historyLoadedRef.current) return;
     historyLoadedRef.current = true;
-    fetch("/api/v1/ai/chat-history?scope=general&limit=50")
-      .then((res) => (res.ok ? res.json() : null))
-      .then((json: { data?: HistoryEntry[] } | null) => {
-        if (json?.data?.length) setMessages(json.data.map((m) => ({ role: m.role, content: m.content })));
-      })
-      .catch(() => {});
+    (async () => {
+      const listRes = await fetch("/api/v1/ai/conversations");
+      const list = listRes.ok ? ((await listRes.json()) as { data: Conversation[] }).data : [];
+      const id = list.length > 0
+        ? list[0]!.id
+        : await fetch("/api/v1/ai/conversations", { method: "POST" })
+            .then((res) => (res.ok ? res.json() : null))
+            .then((created: Conversation | null) => created?.id ?? null);
+      if (!id) return;
+      setConversationId(id);
+      await loadMessages(id);
+    })().catch(() => {});
   }, [open]);
 
   useEffect(() => {
@@ -59,7 +100,7 @@ export function CookingAssistantPanel() {
       const res = await fetch("/api/v1/ai/cooking-chat", {
         method: "POST",
         headers: { "Content-Type": "application/json" },
-        body: JSON.stringify({ question }),
+        body: JSON.stringify({ question, conversationId: conversationId ?? undefined }),
       });
       const data = await res.json() as { answer?: string; error?: string };
       setMessages((prev) => [
@@ -122,7 +163,12 @@ export function CookingAssistantPanel() {
                   {fullscreen ? <Minimize2 className="h-4 w-4" /> : <Maximize2 className="h-4 w-4" />}
                 </button>
                 <ChatHistorySearch />
-                <ClearChatHistoryButton disabled={messages.length === 0} onCleared={() => setMessages([])} />
+                <ConversationMenu
+                  activeId={conversationId}
+                  onSelect={handleSelectConversation}
+                  onCreated={handleConversationCreated}
+                  onDeletedActive={handleActiveConversationDeleted}
+                />
               </div>
             </div>
             <p className="text-xs text-muted-foreground text-left">{t("subtitle")}</p>