fix: queue drain survives navigation away from a streaming conversation

Previously the queue drain guard (currentConversation.id === convId) meant
that if the user navigated to ChatView while a workspace stream was running,
the workspace's queued messages were silently abandoned — they sat in
localStorage indefinitely with no code path to resume them.

- Extract _tryDrainQueue(convId) with the same guard logic
- Call it at stream-end (replaces the inline block)
- Call it in fetchConversation after _loadQueue, so returning to a
  conversation with orphaned queue messages drains them automatically
- Order is now preserved: messages drain in the order they were queued,
  even across navigation events

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/stores/chat.ts

@@ -109,6 +109,28 @@ export const useChatStore = defineStore("chat", () => {
     }
   }
 
+  // Drain the next queued message for a conversation, if conditions are met.
+  // Called both at stream-end and after fetchConversation, so orphaned queue
+  // messages (e.g. from a navigation away mid-stream) are picked up on return.
+  function _tryDrainQueue(convId: number) {
+    const queue = convQueues.value[convId];
+    if (!queue?.length) return;
+    if (isStreamingConv(convId)) return; // stream-end will drain naturally
+    if (currentConversation.value?.id !== convId) return; // not our conversation
+    const next = queue.shift()!;
+    _saveQueue(convId);
+    setTimeout(() => sendMessage(
+      next.content,
+      next.contextNoteId,
+      next.includeNoteIds,
+      next.think,
+      next.contextNoteTitle,
+      next.excludeNoteIds,
+      next.ragProjectId,
+      next.workspaceProjectId,
+    ), 0);
+  }
+
   function clearQueue() {
     const id = currentConversation.value?.id;
     if (id) {
@@ -158,6 +180,9 @@ export const useChatStore = defineStore("chat", () => {
         `/api/chat/conversations/${id}`
       );
       _loadQueue(id);
+      // Drain any messages that were queued but never sent because the user
+      // navigated away before the previous stream finished.
+      _tryDrainQueue(id);
     } catch (e) {
       useToastStore().show("Failed to load conversation", "error");
       throw e;
@@ -431,23 +456,9 @@ export const useChatStore = defineStore("chat", () => {
       s.pendingTool = null;
     }
 
-    // Process next queued message, if any.
-    // Use setTimeout so this frame resolves before the next send begins.
-    const queue = convQueues.value[convId];
-    if (queue?.length && currentConversation.value?.id === convId) {
-      const next = queue.shift()!;
-      _saveQueue(convId);
-      setTimeout(() => sendMessage(
-        next.content,
-        next.contextNoteId,
-        next.includeNoteIds,
-        next.think,
-        next.contextNoteTitle,
-        next.excludeNoteIds,
-        next.ragProjectId,
-        next.workspaceProjectId,
-      ), 0);
-    }
+    // Process next queued message if this is still the active conversation.
+    // If the user has navigated away, _tryDrainQueue will fire on fetchConversation.
+    _tryDrainQueue(convId);
   }
 
   async function reconnectIfGenerating(convId: number): Promise<void> {