diff --git a/client/src/components/ui/sandboxed-iframe.tsx b/client/src/components/ui/sandboxed-iframe.tsx
index 4e22ea8c3..92869569a 100644
--- a/client/src/components/ui/sandboxed-iframe.tsx
+++ b/client/src/components/ui/sandboxed-iframe.tsx
@@ -61,7 +61,7 @@ interface SandboxedIframeProps {
  * SandboxedIframe provides a secure double-iframe architecture per SEP-1865.
  *
  * Message flow:
- * 1. Proxy sends ui/notifications/sandbox-ready when loaded
+ * 1. Proxy sends ui/notifications/sandbox-proxy-ready when loaded
  * 2. Host sends ui/notifications/sandbox-resource-ready with HTML
  * 3. Guest UI initializes and communicates via JSON-RPC 2.0
  */
@@ -157,7 +157,7 @@ export const SandboxedIframe = forwardRef<
         (event.data as { jsonrpc?: string; method?: string }) || {};
       if (jsonrpc !== "2.0") return;
 
-      if (method === "ui/notifications/sandbox-ready") {
+      if (method === "ui/notifications/sandbox-proxy-ready") {
         setProxyReady(true);
         onProxyReady?.();
         return;
diff --git a/server/routes/mcp/sandbox-proxy.html b/server/routes/mcp/sandbox-proxy.html
index ba88151d1..9bb4803c6 100644
--- a/server/routes/mcp/sandbox-proxy.html
+++ b/server/routes/mcp/sandbox-proxy.html
@@ -250,7 +250,7 @@
       window.parent.postMessage(
         {
           jsonrpc: "2.0",
-          method: "ui/notifications/sandbox-ready",
+          method: "ui/notifications/sandbox-proxy-ready",
           params: {},
         },
         "*",