Let workers ask each other through the coordinator in chatrooms

A worker asks for another bot's help with ask_crew. The coordinator
reads the request, asks the right bot (in a workspace, only its
members), and sends the answer back into the asking bot's
conversation, waking it. Each exchange is kept as a read-only
chatroom: listed in the main rail after the workspaces, or in the
workspace's rail for requests made there, with live status rows for
each bot while it's open and a Stop button.

Room sessions are hidden from every conversation list, other bots'
words reach the model fenced as data, and turns, nesting and open
rooms are capped. Closed rooms are pruned after a retention period
and past a cap per place (Settings > General).

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

src/functions/backend/db/chatrooms/prune-chatrooms-sql.ts

@@ -0,0 +1,46 @@
+type Params = {
+    /**
+     * Closed rooms that last moved before this are deleted.
+     */
+    cutoff: number;
+    /**
+     * How many rooms one place keeps, open ones counted.
+     */
+    max_per_place: number;
+    /**
+     * Only this place: a workspace, or (null) bots' own chats. Left out,
+     * every place.
+     */
+    workspace_id?: number | null;
+};
+
+/**
+ * The ids of the rooms past retention: closed ones older than the cutoff,
+ * and closed ones past the newest `max_per_place` rooms of their place
+ * (ranked by last activity, open rooms counted but never picked). A room a
+ * still-open room was asked from is kept, so a chain is never cut while it
+ * runs.
+ */
+export default function pruneChatroomsSql({ cutoff, max_per_place, workspace_id }: Params) {
+    const scoped = workspace_id !== undefined;
+
+    return {
+        sql: `SELECT id FROM (
+                SELECT c.id, c.status,
+                    COALESCE(c.closed_at, c.last_activity_at, c.created_at) AS moved_at,
+                    ROW_NUMBER() OVER (
+                        PARTITION BY COALESCE(c.workspace_id, 0)
+                        ORDER BY COALESCE(c.last_activity_at, c.created_at) DESC, c.id DESC
+                    ) AS place_rank
+                FROM chatrooms c
+                ${scoped ? `WHERE c.workspace_id IS ?` : ""}
+            ) ranked
+            WHERE status != 'open'
+                AND (moved_at < ? OR place_rank > ?)
+                AND NOT EXISTS (SELECT 1 FROM chatrooms child WHERE child.parent_chatroom_id = ranked.id AND child.status = 'open')`,
+        values: [...(scoped ? [workspace_id ? Number(workspace_id) : null] : []), cutoff, Math.max(1, max_per_place)] as (
+            | string
+            | number
+        )[],
+    };
+}