fix: stop the composer re-sending a queued message already in flight

A queued message is removed from the queue only after its send resolves,
so between dispatch and resolution it stays visible to every reader — and
a composer submit merges the whole queue into its own send. Over a relay
that window is seconds, long enough to deliver the same message twice.

The queue now tracks which entries are awaiting the server. Dispatchers
skip them, clearQueue retains them so the pending send can still remove
or restore its own entry, and the flag is not persisted because a restart
has no in-flight sends.

packages/ui/src/components/chat/ChatInput.tsx

@@ -159,6 +159,7 @@ const MAX_MOBILE_COMPOSER_LINES = 16;
  */
 const MOBILE_COMPOSER_BOUND_GAP_PX = 4;
 const EMPTY_QUEUE: QueuedMessage[] = [];
+const EMPTY_SENDING_IDS: string[] = [];
 const COMPACT_CHAT_PLACEHOLDER_MAX_WIDTH = 560;
 const renameFileForAttachmentCitation = (file: File, filename: string): File => {
     if (file.name === filename) {
@@ -945,9 +946,16 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                 hasContent: options.presetText.trim().length > 0 || attachedFiles.length > 0 || hasDrafts,
             }
             : getCurrentInputSnapshot();
-        const queuedMessagesToSend = queuedMessageId
+        // A queued item stays in the queue until its own send resolves, so the
+        // auto-send hook may already be delivering one of these. Merging it here
+        // would send the same message twice (the window is seconds over a relay).
+        const sendingIds = messageQueueTarget
+            ? useMessageQueueStore.getState().sendingIds[getMessageQueueKey(messageQueueTarget)] ?? EMPTY_SENDING_IDS
+            : EMPTY_SENDING_IDS;
+        const queuedMessagesToSend = (queuedMessageId
             ? queuedMessages.filter((message) => message.id === queuedMessageId)
-            : queuedMessages;
+            : queuedMessages
+        ).filter((message) => !sendingIds.includes(message.id));
 
         if (queuedOnly && autoReviewRunning) {
             return;