fix: videos disappear after auto-reset or localStorage quota failure

Root causes:
1. Auto-reset calls store.clearMessages(), wiping messages from
localStorage. Any subsequent loadConversation() (sidebar click,
new chat then back) read from the now-empty store, losing the
video.
2. Large video base64 dataUrls can exceed localStorage quota; the
message is never persisted, so it vanishes on any reload.

Fix: add this._sessionMessages (Map<convId, messages[]>) as an
in-memory cache for the current page session.

- Every user/assistant message is pushed to _sessionMessages in
addition to (or instead of, when quota fails) localStorage.
- _selectConversation and _loadCurrentConversation use
_sessionConvFor(conv) which substitutes the in-memory messages
when available, so media dataUrls survive auto-resets and quota
failures for the lifetime of the page.
- Auto-reset (store.clearMessages) does NOT clear _sessionMessages —
it only resets the API context, not the visual history.
- /clean explicitly calls _clearSessionMsgs so the user's manual
wipe still works correctly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/components/app.js

@@ -21,6 +21,10 @@ export class App {
     this.modelPicker = new ModelPicker();
     this.settingsModal = new SettingsModal();
     this._sidebarOpen = false;
+    // In-memory message cache keyed by convId.  Persists for the page session so
+    // that media (video/image dataUrls) remains visible even after an auto-reset
+    // clears localStorage, or when localStorage quota prevents persistence.
+    this._sessionMessages = new Map();
   }
 
   init() {
@@ -34,6 +38,25 @@ export class App {
     this.inputBar.focus();
   }
 
+  // --- Session message cache helpers ---
+
+  _pushSessionMsg(convId, msg) {
+    if (!this._sessionMessages.has(convId)) this._sessionMessages.set(convId, []);
+    this._sessionMessages.get(convId).push(msg);
+  }
+
+  _clearSessionMsgs(convId) {
+    this._sessionMessages.delete(convId);
+  }
+
+  // Returns a conv-like object backed by in-memory messages when available,
+  // so that media dataUrls survive auto-resets and localStorage quota failures.
+  _sessionConvFor(conv) {
+    if (!conv) return conv;
+    const mem = this._sessionMessages.get(conv.id);
+    return mem?.length ? { ...conv, messages: mem } : conv;
+  }
+
   _render() {
     this.root.className = 'flex h-screen overflow-hidden bg-[var(--c-bg)]';
 
@@ -155,7 +178,7 @@ export class App {
     if (currentId) {
       const conv = store.getCurrentConversation();
       if (conv) {
-        this.chat.loadConversation(conv);
+        this.chat.loadConversation(this._sessionConvFor(conv));
         this.modelPicker.syncToConversation(conv);
         this.inputBar.setModel(this.modelPicker.getModel());
         this._updateContextInfo();
@@ -188,7 +211,7 @@ export class App {
       this._updateContextInfo();
       return;
     }
-    this.chat.loadConversation(conv);
+    this.chat.loadConversation(this._sessionConvFor(conv));
     this.modelPicker.syncToConversation(conv);
     this.inputBar.setModel(this.modelPicker.getModel());
     this.sidebar.update();
@@ -206,6 +229,7 @@ export class App {
       const convId = store.getCurrentConversationId();
       if (convId) {
         store.clearMessages(convId);
+        this._clearSessionMsgs(convId);
         this.chat.clear();
         this._updateContextInfo();
       }
@@ -260,6 +284,7 @@ export class App {
     try {
       this.chat.clearError();
       store.addMessage(convId, userMessage);
+      this._pushSessionMsg(convId, userMessage);
       this.chat.appendUserMessage(userMessage);
       this._updateContextInfo();
       renderOk = true;
@@ -305,11 +330,13 @@ export class App {
 
       // Finalize
       this.chat.finalizeAssistantMessage(fullText);
-      store.addMessage(convId, {
+      const assistantMsg = {
         role: 'assistant',
         content: fullText,
         timestamp: new Date().toISOString(),
-      });
+      };
+      store.addMessage(convId, assistantMsg);
+      this._pushSessionMsg(convId, assistantMsg);
       this._updateContextInfo();
       this.sidebar.update();
     } catch (err) {
@@ -360,6 +387,7 @@ export class App {
   async _handleAudioTask({ convId, model, settings, instruction, audio }) {
     const userMessage = this._buildAudioUserMessage(audio, instruction);
     store.addMessage(convId, userMessage);
+    this._pushSessionMsg(convId, userMessage);
     this.chat.appendUserMessage(userMessage);
     this._updateContextInfo();
 
@@ -380,11 +408,13 @@ export class App {
         this.chat.hideTypingIndicator();
         this.chat.startAssistantMessage();
         this.chat.finalizeAssistantMessage(transcript);
-        store.addMessage(convId, {
+        const assistantMsg = {
           role: 'assistant',
           content: transcript,
           timestamp: new Date().toISOString(),
-        });
+        };
+        store.addMessage(convId, assistantMsg);
+        this._pushSessionMsg(convId, assistantMsg);
         this._updateContextInfo();
         this.sidebar.update();
         return;
@@ -418,11 +448,13 @@ export class App {
       }
 
       this.chat.finalizeAssistantMessage(fullText);
-      store.addMessage(convId, {
+      const assistantMsg = {
         role: 'assistant',
         content: fullText,
         timestamp: new Date().toISOString(),
-      });
+      };
+      store.addMessage(convId, assistantMsg);
+      this._pushSessionMsg(convId, assistantMsg);
       this._updateContextInfo();
       this.sidebar.update();
     } catch (err) {