Load a conversation's history on the client

The conversation pages rendered their messages on the server, so a page
the back button restored from the back-forward cache showed an old
thread. The server now renders everything else (rail, header, composer)
and the history (active session, latest messages, active task) loads
from api/admin/bots/conversation-history once the page is on screen,
with a loading line under the header, and again on a pageshow restore.
Messages sent or pushed while it loads are merged with it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/functions/backend/db/bot-sessions/grab-conversation-history.ts

@@ -0,0 +1,67 @@
+import { AppData } from "@/src/data/app-data";
+import type { ConversationHistory } from "@/src/types";
+import grabActiveBotTask from "../bots/grab-active-bot-task";
+import grabBotMessages from "../bots/grab-bot-messages";
+import ensureBotSession from "./ensure-bot-session";
+import grabUserConversation from "./grab-user-conversation";
+import markBotSessionRead from "./mark-bot-session-read";
+
+type Params = {
+    user_id: number;
+    bot_id: number | string;
+    /**
+     * The workspace the conversation is in; none for the bot's own chat.
+     */
+    workspace_id?: number | string | null;
+};
+
+/**
+ * A conversation's history, which the conversation pages load on the
+ * client once they render (`api/admin/bots/conversation-history`): the
+ * bot's active session there (marked read), its latest
+ * `AppData.ConversationFirstMessages` messages (the thread loads older
+ * ones as it scrolls) and the bot's active task in it. Everything else on
+ * the page comes with it from the server (`grabConversationProps`).
+ * Null when the user can't chat with the bot there.
+ */
+export default async function grabConversationHistory({
+    user_id,
+    bot_id,
+    workspace_id,
+}: Params): Promise<ConversationHistory | null> {
+    const conversation = await grabUserConversation({ user_id, bot_id, workspace_id }).catch(
+        () => null,
+    );
+
+    if (!conversation?.bot?.id) return null;
+
+    const open_bot_id = conversation.bot.id;
+    const session = await ensureBotSession({
+        user_id,
+        bot_id: open_bot_id,
+        workspace_id: conversation.workspace_id,
+    });
+
+    if (session.unread) {
+        await markBotSessionRead({ session_id: session.id!, user_id });
+        session.unread = 0;
+    }
+
+    const [messages, task] = await Promise.all([
+        grabBotMessages({
+            session_id: session.id!,
+            user_id,
+            limit: AppData.ConversationFirstMessages + 1,
+        }),
+        grabActiveBotTask({ bot_id: open_bot_id, session_id: session.id }),
+    ]);
+
+    const has_more = messages.length > AppData.ConversationFirstMessages;
+
+    return {
+        session,
+        messages: has_more ? messages.slice(1) : messages,
+        has_more,
+        task,
+    };
+}