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/past-session-messages-sql.test.ts

@@ -0,0 +1,77 @@
+import { Database } from "bun:sqlite";
+import { describe, expect, test } from "bun:test";
+import searchPastSessionsSql, { type SearchPastSessionsParams } from "./past-session-messages-sql";
+
+/**
+ * A bot's search of its earlier sessions reads only that user's
+ * conversation with it (in the same place), never the session it's
+ * answering. Run against real SQLite.
+ */
+const db = new Database(":memory:");
+
+db.run(`CREATE TABLE bot_sessions (id INTEGER PRIMARY KEY, user_id INTEGER, bot_id INTEGER, workspace_id INTEGER, title TEXT)`);
+db.run(`CREATE TABLE bot_messages (id INTEGER PRIMARY KEY, session_id INTEGER, author TEXT, text TEXT, created_at INTEGER)`);
+db.run(`INSERT INTO bot_sessions VALUES
+    (1, 1, 10, NULL, 'Invoices'),
+    (2, 1, 10, NULL, 'Current'),
+    (3, 2, 10, NULL, 'Another user'),
+    (4, 1, 11, NULL, 'Another bot'),
+    (5, 1, 10, 7, 'In a workspace')`);
+db.run(`INSERT INTO bot_messages (id, session_id, author, text) VALUES
+    (1, 1, 'user', 'Send the Acme invoice to [email protected]'),
+    (2, 1, 'bot', 'Done: invoice INV-42 sent to Acme.'),
+    (3, 2, 'user', 'What happened with the Acme invoice?'),
+    (4, 3, 'user', 'Acme invoice for someone else'),
+    (5, 4, 'user', 'Acme invoice to another bot'),
+    (6, 5, 'user', 'Acme invoice in the workspace'),
+    (7, 1, 'user', 'Discount of 100% off'),
+    (8, 1, 'user', 'Discount of 10 off')`);
+
+function ids(params: Partial<SearchPastSessionsParams>) {
+    const { sql, values } = searchPastSessionsSql({
+        user_id: 1,
+        bot_id: 10,
+        current_session_id: 2,
+        query: "",
+        ...params,
+    });
+
+    return (db.query(sql).all(...values) as { id: number }[]).map((row) => row.id);
+}
+
+describe("searchPastSessionsSql", () => {
+    test("finds only this conversation's earlier sessions, newest first", () => {
+        expect(ids({ query: "acme invoice" })).toEqual([2, 1]);
+    });
+
+    test("keeps the workspace's conversation apart from the bot's own chat", () => {
+        expect(ids({ query: "acme", workspace_id: 7, current_session_id: 99 })).toEqual([6]);
+    });
+
+    test("every word must match", () => {
+        expect(ids({ query: "invoice INV-42" })).toEqual([2]);
+    });
+
+    test("% matches only itself", () => {
+        expect(ids({ query: "100%" })).toEqual([7]);
+    });
+
+    test("pages with before_id", () => {
+        expect(ids({ query: "acme", before_id: 2 })).toEqual([1]);
+    });
+
+    test("cuts the text around the match", () => {
+        const { sql, values } = searchPastSessionsSql({
+            user_id: 1,
+            bot_id: 10,
+            current_session_id: 2,
+            query: "billing",
+            snippet_chars: 12,
+        });
+        const row = db.query(sql).get(...values) as { snippet: string; session_title: string };
+
+        expect(row.snippet).toContain("billing");
+        expect(row.snippet.length).toBeLessThanOrEqual(12);
+        expect(row.session_title).toBe("Invoices");
+    });
+});