Give every task a bot: drop shared workspace tasks

A workspace task with no bot was seen by every bot working there. Now a
task can't be saved without a bot, a worker reaches only its own (the
workspace admin and the coordinator still reach all), the workspace page
picks who has a new task, and a bot leaving a workspace or deleted passes
its tasks there to the workspace's admin bot, else the coordinator (also
at boot for rows without a bot).

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

src/functions/backend/db/tasks/grab-tasks.ts

@@ -27,10 +27,6 @@ type Params = {
      * Only the tasks this bot has (anywhere, unless narrowed).
      */
     only_bot_id?: number | string | null;
-    /**
-     * With `only_bot_id`: also the shared ones nobody has yet.
-     */
-    with_unassigned?: boolean;
     /**
      * Only one workspace's tasks.
      */
@@ -61,7 +57,6 @@ export default async function grabTasks({
     is_coordinator,
     admin_workspace_ids,
     only_bot_id,
-    with_unassigned,
     only_workspace_id,
     own_list,
     statuses,
@@ -82,7 +77,7 @@ export default async function grabTasks({
     }
 
     if (only_bot_id) {
-        where.push(with_unassigned ? `(t.bot_id = ? OR t.bot_id IS NULL)` : `t.bot_id = ?`);
+        where.push(`t.bot_id = ?`);
         values.push(Number(only_bot_id));
     }