security: whitelist message types in content script relay

Add an ALLOWED_TYPES whitelist to validate the type field from page
events before forwarding to the background script. Previously, the
type field came directly from the page with no validation, and the
spread operator forwarded arbitrary fields, allowing a malicious page
to invoke internal extension message handlers or inject unexpected
data. Now only known NIP message types are forwarded, and only safe
fields per message type are included in the forwarded message.

Co-Authored-By: claude-flow <ruv@ruv.net>

Author: DreamLab-AI Mega-Sprint

src/injected.js

@@ -314,17 +314,47 @@ script.onload = function () {
 };
 (document.head || document.documentElement).appendChild(script);
 
+// Allowed message types that can be forwarded to the background script
+const ALLOWED_TYPES = new Set([
+  'GET_PUBLIC_KEY',
+  'SIGN_EVENT',
+  'GET_RELAYS',
+  'NIP04_ENCRYPT',
+  'NIP04_DECRYPT',
+  'NIP44_ENCRYPT',
+  'NIP44_DECRYPT'
+]);
+
 // Listen for requests from the injected script
 window.addEventListener('podkey-request', async (event) => {
   const { id, type, ...data } = event.detail;
 
   console.log('[Podkey] Received request:', type, 'from page');
 
+  if (!ALLOWED_TYPES.has(type)) {
+    console.warn('[Podkey] Rejected unknown request type:', type);
+    window.dispatchEvent(new CustomEvent('podkey-response', {
+      detail: { id, error: 'Unknown request type' }
+    }));
+    return;
+  }
+
+  // Only forward known safe fields per message type
+  const safeData = {};
+  if (type === 'SIGN_EVENT' && data.event) {
+    safeData.event = data.event;
+  } else if ((type === 'NIP04_ENCRYPT' || type === 'NIP04_DECRYPT' ||
+              type === 'NIP44_ENCRYPT' || type === 'NIP44_DECRYPT')) {
+    if (data.peer) safeData.peer = String(data.peer);
+    if (data.plaintext !== undefined) safeData.plaintext = String(data.plaintext || '');
+    if (data.ciphertext !== undefined) safeData.ciphertext = String(data.ciphertext);
+  }
+
   try {
-    // Forward to background script
+    // Forward to background script with only validated fields
     const response = await chrome.runtime.sendMessage({
       type,
-      ...data,
+      ...safeData,
       origin: window.location.origin
     });