feat(chat): add client encryption and key lifecycle

extension/chat-wire.js

@@ -0,0 +1,11 @@
+export function buildChatRelayPayload(ciphertext) {
+    return { ciphertext };
+}
+
+export function encodeSocketEvent(event, data, forbiddenSecret = '') {
+    const payload = JSON.stringify([event, data]);
+    if (forbiddenSecret && payload.includes(forbiddenSecret)) {
+        throw new Error('Refusing to send chat secret to relay');
+    }
+    return `42${payload}`;
+}