perf(convex): bound unbounded owner-wide collects on hot paths

packages/backend/convex/agentJobs.ts

@@ -234,6 +234,11 @@ const normalizeWorkspacePaths = (values: string[] | undefined, max: number) =>
     .filter((value, index, all) => all.indexOf(value) === index)
     .slice(0, max);
 
+// Owner-wide scans for old-workspace cleanup are bounded to this many rows so
+// the query cost cannot grow without limit. The count is therefore reported as
+// "up to N"; delete is per-call bounded and re-runnable to drain the rest.
+const OLD_WORKSPACE_SCAN_LIMIT = 500;
+
 const isDeletableWorkspace = (job: Doc<'agentJobs'>) =>
   ['failed', 'cancelled', 'timed_out'].includes(job.status) ||
   ['stopped', 'expired', 'failed'].includes(job.workspaceStatus ?? '');
@@ -1069,7 +1074,7 @@ export const countOldWorkspaces = query({
     const jobs = await ctx.db
       .query('agentJobs')
       .withIndex('by_owner', (q) => q.eq('ownerId', ownerId))
-      .collect();
+      .take(OLD_WORKSPACE_SCAN_LIMIT);
     return jobs.filter(
       (job) => isDeletableWorkspace(job) && job.updatedAt <= cutoff,
     ).length;
@@ -1091,7 +1096,7 @@ export const deleteOldWorkspaces = mutation({
     const jobs = await ctx.db
       .query('agentJobs')
       .withIndex('by_owner', (q) => q.eq('ownerId', ownerId))
-      .collect();
+      .take(OLD_WORKSPACE_SCAN_LIMIT);
     const deletable = jobs
       .filter((job) => isDeletableWorkspace(job) && job.updatedAt <= cutoff)
       .sort((a, b) => a.updatedAt - b.updatedAt)