fix(queue): clear the queue card after the last queued message is sent

When the server delivered the last item of a session's queue it deleted
the session entry and broadcast the update with an empty directory. The
UI keys its projection by directory, could not build the key, and dropped
the event, so the delivered message stayed in the "Queued messages" card
until the next full hydration.

The server now remembers a session's directory beyond the emptying of its
queue so that broadcast names it. The UI additionally treats an empty
session without a directory as "this session's queue is done" for every
projection keyed under that session id, which covers clients talking to
an older server.

Claude-Session: https://claude.ai/code/session_01VqV56Hez25hTxXH4ipJfzH

packages/web/server/lib/message-queue/runtime.js

@@ -220,6 +220,10 @@ export function createMessageQueueRuntime({
   const failures = new Map(); // sessionId → { itemId, failures, nextAttemptAt }
   const abortedAt = new Map(); // sessionId → timestamp
   const holds = new Map(); // sessionId → expiresAt
+  // sessionId → directory, kept after the queue empties: the UI keys its
+  // projection by directory, so the broadcast that removes the last item must
+  // still name it or the client cannot tell which queue just finished.
+  const directories = new Map();
 
   // --- persistence ---------------------------------------------------------
 
@@ -302,7 +306,7 @@ export function createMessageQueueRuntime({
     const queue = queues.get(sessionId);
     return {
       sessionId,
-      directory: queue?.directory ?? '',
+      directory: queue?.directory ?? directories.get(sessionId) ?? '',
       items: (queue?.items ?? []).map(toPublicItem),
       sendingId: sending.get(sessionId) ?? null,
     };
@@ -329,6 +333,7 @@ export function createMessageQueueRuntime({
   };
 
   const setQueueItems = (sessionId, directory, items) => {
+    directories.set(sessionId, directory);
     if (items.length === 0) {
       queues.delete(sessionId);
       return;
@@ -564,6 +569,7 @@ export function createMessageQueueRuntime({
     const existing = queues.get(sessionId);
     const items = [...(existing?.items ?? []), item].slice(-MAX_ITEMS_PER_SESSION);
     queues.set(sessionId, { directory, items });
+    directories.set(sessionId, directory);
     if (queues.size > MAX_SESSIONS) {
       const oldest = Array.from(queues.entries())
         .filter(([id]) => id !== sessionId && !sending.has(id))
@@ -573,6 +579,7 @@ export function createMessageQueueRuntime({
         queues.delete(staleId);
         clearTimer(staleId);
         broadcast(staleId);
+        directories.delete(staleId);
       }
     }
     const result = commit(sessionId);
@@ -675,6 +682,7 @@ export function createMessageQueueRuntime({
       clearTimer(deletedSessionId);
       failures.delete(deletedSessionId);
       commit(deletedSessionId);
+      directories.delete(deletedSessionId);
       return;
     }