Assistant: hydrate the persisted thread in the UI

- Asistente.tsx pins threadId "main" on CopilotChat (an explicit stable
  id stops the per-mount message wipe), runs a hydration pass on page
  load — an empty-messages run makes MAF replay the stored snapshot as
  MESSAGES_SNAPSHOT with no LLM call — and sends the Inicio ask-box
  question only after hydration so every normal run carries the full
  client-known history. "Nueva conversación" clears the stored thread
  behind a ConfirmDialog.
- server.ts: the BFF no longer injects context into empty-messages
  requests (that would defeat MAF's hydration trigger), and the snapshot
  reconciliation passes hydration replays through untouched and treats
  ids the client already sent as history rather than duplicates.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/pages/Asistente.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef } from "react";
+import { useEffect, useRef, useState } from "react";
 import { useLocation, useNavigate } from "react-router-dom";
 import {
   CopilotChat,
@@ -7,10 +7,17 @@ import {
   useCopilotKit,
 } from "@copilotkit/react-core/v2";
 import { useCopilotAction } from "@copilotkit/react-core";
-import { Sparkles } from "lucide-react";
+import { MessageSquarePlus, Sparkles } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import ConfirmDialog from "@/components/ConfirmDialog";
 import { PageHeader } from '@/components/page-header';
 import { SpendingSummaryCard, type SpendingSummaryArgs } from "@/components/chat/ChatCards";
 
+// Single persistent conversation: the backend snapshot store keys on this
+// same id (backend/app/api/v1/endpoints/chat.py). An explicit, stable
+// threadId also stops CopilotChat from wiping messages on remount.
+const CHAT_THREAD_ID = "main";
+
 const STATIC_SUGGESTIONS = {
   available: "before-first-message" as const,
   suggestions: [
@@ -24,28 +31,66 @@ const STATIC_SUGGESTIONS = {
 export default function Asistente() {
   useConfigureSuggestions(STATIC_SUGGESTIONS);
 
-  // A question typed on the Inicio dashboard arrives via router state:
-  // append it as a user message and run the agent once.
   const location = useLocation();
   const navigate = useNavigate();
   const { agent } = useAgent({ agentId: "wealthysmart" });
   const { copilotkit } = useCopilotKit();
-  const sentRef = useRef(false);
+  const [confirmClear, setConfirmClear] = useState(false);
+  const [clearing, setClearing] = useState(false);
+
+  // Boot sequence, once per page load: hydrate the persisted thread, then
+  // send any question that arrived from the Inicio ask-box via router state.
+  // Order matters — hydration first keeps the invariant that every normal
+  // run's input carries the full client-known history (the BFF's snapshot
+  // reconciliation relies on it).
+  const bootRef = useRef(false);
   useEffect(() => {
+    if (!agent || bootRef.current) return;
+    bootRef.current = true;
     const ask = (location.state as { ask?: string } | null)?.ask;
-    if (!ask || sentRef.current || !agent) return;
-    sentRef.current = true;
-    // Clear the state so back/refresh doesn't re-send the question.
-    navigate(location.pathname, { replace: true, state: null });
-    agent.addMessage({
-      id: crypto.randomUUID(),
-      role: "user",
-      content: ask,
-    });
-    void copilotkit.runAgent({ agent });
+    if (ask) {
+      // Clear the state so back/refresh doesn't re-send the question.
+      navigate(location.pathname, { replace: true, state: null });
+    }
+    void (async () => {
+      agent.threadId = CHAT_THREAD_ID;
+      if (agent.messages.length === 0) {
+        // Empty-messages run = MAF's hydration trigger: replays the stored
+        // snapshot as MESSAGES_SNAPSHOT without invoking the LLM.
+        try {
+          await copilotkit.runAgent({ agent });
+        } catch (err) {
+          console.error("[asistente] thread hydration failed:", err);
+        }
+      }
+      if (ask) {
+        agent.addMessage({
+          id: crypto.randomUUID(),
+          role: "user",
+          content: ask,
+        });
+        void copilotkit.runAgent({ agent });
+      }
+    })();
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [agent]);
 
+  const clearThread = async () => {
+    setClearing(true);
+    try {
+      await fetch("/api/v1/chat/thread", {
+        method: "DELETE",
+        credentials: "include",
+      });
+      agent?.setMessages([]);
+      setConfirmClear(false);
+    } catch (err) {
+      console.error("[asistente] clear thread failed:", err);
+    } finally {
+      setClearing(false);
+    }
+  };
+
   useCopilotAction({
     name: "render_spending_summary",
     description:
@@ -92,12 +137,35 @@ export default function Asistente() {
           icon={Sparkles}
           title="Asistente"
           subtitle="Pregúntale a WealthySmart sobre tus finanzas."
+          actions={
+            <Button
+              variant="outline"
+              size="sm"
+              onClick={() => setConfirmClear(true)}
+              disabled={!agent || agent.messages.length === 0}
+            >
+              <MessageSquarePlus />
+              Nueva conversación
+            </Button>
+          }
         />
       </div>
 
+      {confirmClear && (
+        <ConfirmDialog
+          title="¿Nueva conversación?"
+          message="Se borrará el historial del chat guardado. Esta acción no se puede deshacer."
+          confirmLabel="Borrar historial"
+          onConfirm={clearThread}
+          onCancel={() => setConfirmClear(false)}
+          loading={clearing}
+        />
+      )}
+
       <div className="flex-1 min-h-0 rounded-xl border border-border overflow-hidden bg-card">
         <CopilotChat
           className="h-full"
+          threadId={CHAT_THREAD_ID}
           labels={{
             modalHeaderTitle: "WealthySmart",
             welcomeMessageText: "¿Qué quieres saber sobre tus finanzas?",