fix(acp): Replace optimistic message in-place to preserve order

The previous approach removed the optimistic message and appended the
persisted version at the end of the array, which broke chronological
order when assistant messages had already been added after it.
Now uses `findIndex` + in-place replacement to keep the message at
its correct position in the chat history.

Author: wilcorrea

apps/tauri/src/hooks/useSessionMessages.ts

@@ -95,10 +95,16 @@ export function useSessionMessages(sessionId: string): UseSessionMessagesReturn
       if (msgSessionId !== sessionId) return;
       setMessages((prev) => {
         if (prev.some((m) => m.id === id)) return prev;
-        const withoutOptimistic = prev.filter(
-          (m) => !(m.id.startsWith("optimistic-") && m.role === "user" && m.content === content)
+        const idx = prev.findIndex(
+          (m) => m.id.startsWith("optimistic-") && m.role === "user" && m.content === content
         );
-        return [...withoutOptimistic, { id, role: "user", content, timestamp: new Date() }];
+        const persisted: AcpMessage = { id, role: "user", content, timestamp: new Date() };
+        if (idx >= 0) {
+          const updated = [...prev];
+          updated[idx] = persisted;
+          return updated;
+        }
+        return [...prev, persisted];
       });
     });
     return () => { void unlisten.then((fn) => fn()); };