Carry conversations into new sessions with a visible summary

- Bots get continue_in_new_session: the bot writes a title and summary,
  the session closes for good (read-only) and the new one opens with the
  summary as a "Carried over from the last session" message that links
  back to the old session.
- Continue in new session (conversation menu, sessions modal) and the
  automatic rollover at the session length do the same; New session now
  starts a fresh, unlinked session.
- Session length is an app setting in Settings > General.
- ?session_id= opens a session; a carried-over one shows a bar linking to
  where the conversation went on instead of the composer.
- The thread can open the previous session above the current one (shown
  only, never in the prompt), and replies get search_past_sessions and
  read_past_session.
- Sessions are named from their opening messages, not their latest, and
  a carried summary is labelled as the earlier session's.

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

src/functions/backend/db/bot-sessions/start-bot-session.ts

@@ -13,10 +13,11 @@ type Params = {
 };
 
 /**
- * Closes the conversation's active session and starts the next one, which
- * carries on from it (its summary goes into the next reply's prompt,
- * rewritten first when it covers fewer messages than the session ended
- * with). An active session with no messages yet is kept as it is.
+ * New session: closes the conversation's active session and starts a
+ * fresh one, linked to nothing and carrying nothing over. Carrying a
+ * conversation on is `carryOverBotSession` (the bot, Continue in new
+ * session, the rollover). An active session with no messages yet is kept
+ * as it is.
  */
 export default async function startBotSession({
     user_id,
@@ -41,10 +42,5 @@ export default async function startBotSession({
         });
     }
 
-    return await createBotSession({
-        user_id,
-        bot_id,
-        workspace_id,
-        previous_session_id: active?.id || null,
-    });
+    return await createBotSession({ user_id, bot_id, workspace_id });
 }