fix: allow re-detailing phases after all tasks are deleted

The "Detail Tasks" button was hidden when an idle detail agent from a
previous run was still associated with the phase. The frontend gate
blocked any re-detail while a detail agent existed, even if it was idle
(i.e. done). The backend already auto-dismisses stale idle agents, so
the frontend just needed to allow idle agents through the gate.

apps/web/src/components/execution/PhaseActions.tsx

@@ -19,9 +19,12 @@ export function PhaseActions({
   const detailMutation = trpc.spawnArchitectDetail.useMutation();
   const [isDetailingAll, setIsDetailingAll] = useState(false);
 
-  // Phases eligible for detailing: no tasks AND no active detail agent
+  // Phases eligible for detailing: no tasks AND no actively running detail agent
   const eligiblePhaseIds = useMemo(
-    () => phasesWithoutTasks.filter((id) => !detailAgentByPhase.has(id)),
+    () => phasesWithoutTasks.filter((id) => {
+      const agent = detailAgentByPhase.get(id);
+      return !agent || agent.status === "idle";
+    }),
     [phasesWithoutTasks, detailAgentByPhase],
   );
 

apps/web/src/components/execution/PhaseDetailPanel.tsx

@@ -207,7 +207,7 @@ export function PhaseDetailPanel({
     detailAgent?.status === "running" ||
     detailAgent?.status === "waiting_for_input";
   const showDetailButton =
-    !detailAgent && !hasTasks;
+    !hasTasks && (!detailAgent || detailAgent.status === "idle");
   const showChangeSet =
     detailAgent?.status === "idle" && !!latestChangeSet;