Keep only the bot cookie for the last visited bot

A workspace conversation is never remembered, so /admin/bots always
reopens the bot's own chat.

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

@@ -3,38 +3,30 @@ import grabUserConversation from "./grab-user-conversation";
 type Params = {
     user_id: number | string;
     bot_id: number | string;
-    /**
-     * Null or undefined: the bot's own chat.
-     */
-    workspace_id?: number | string | null;
 };
 
 export type ReachableConversation = {
     bot_id: number;
-    workspace_id: number | null;
 };
 
 /**
- * A conversation from the last-visited cookie, only while the user still
+ * The bot's own chat from the last-visited cookie, only while the user still
  * reaches it: `grabUserConversation` is the same access check the
- * conversation pages use, so a revoked grant, a deleted bot or an archived
- * workspace answers null and the landing page falls back instead of
- * redirecting into a page that would bounce it back.
+ * conversation pages use, so a revoked grant or a deleted bot answers null
+ * and the landing page falls back instead of redirecting into a page that
+ * would bounce it back.
  */
 export default async function grabReachableConversation({
     user_id,
     bot_id,
-    workspace_id,
 }: Params): Promise<ReachableConversation | null> {
-    const resolved_workspace_id = workspace_id ? Number(workspace_id) : null;
-
     const conversation = await grabUserConversation({
         user_id,
         bot_id,
-        workspace_id: resolved_workspace_id,
+        workspace_id: null,
     }).catch(() => null);
 
     if (!conversation?.bot.id) return null;
 
-    return { bot_id: conversation.bot.id, workspace_id: conversation.workspace_id };
+    return { bot_id: conversation.bot.id };
 }