feat(crypto): sender-key per-conversation multi-device E2EE

apps/desktop/src/components/AppShell.tsx

@@ -1,17 +1,25 @@
 import { useEffect } from 'react';
 import { Outlet } from 'react-router-dom';
 
+import { useAuth } from '../context/AuthContext';
+import { startConversationKeySync } from '../lib/conversationKeySync';
 import { ensureNotificationPermission } from '../lib/osNotify';
 import { CallUI } from './CallUI';
 import { Sidebar } from './Sidebar';
 
 export function AppShell() {
+  const { session, device } = useAuth();
   useEffect(() => {
     // Prompt once per authenticated shell mount. Module-level guard prevents
     // re-asking if the user already responded this session.
     void ensureNotificationPermission();
   }, []);
 
+  useEffect(() => {
+    if (!session?.user.id || !device?.id) return;
+    return startConversationKeySync(session.user.id, device.id);
+  }, [session?.user.id, device?.id]);
+
   return (
     <div className="relative flex min-h-screen overflow-hidden bg-ink-950 text-neutral-100">
       <ShellBackground />

apps/desktop/src/components/MessageBubble.tsx

@@ -98,6 +98,8 @@ export function MessageBubble({
         messageId: message.id,
         conversationId,
         newPlaintext: trimmed,
+        senderUserId: session.user.id,
+        senderDeviceId: device.id,
         senderPrivateKey: priv,
       });
       setEditing(false);