fix: Improve error handling for NIP-86 network/CORS errors

- Add Nip86NetworkError class to detect CORS and network failures
- Provide helpful error message when fetch fails due to CORS
- Update RelayAdminViewer to show specific CORS error messaging

src/components/RelayAdminViewer.tsx

@@ -31,6 +31,7 @@ import {
 import {
   Nip86Client,
   Nip86AuthError,
+  Nip86NetworkError,
   categoryHasMethods,
 } from "@/lib/nip86-client";
 import accountManager from "@/services/accounts";
@@ -92,6 +93,13 @@ export function RelayAdminViewer({ url }: RelayAdminViewerProps) {
     } catch (error) {
       if (error instanceof Nip86AuthError) {
         setMethodsError("Unauthorized - you may not have admin access");
+      } else if (error instanceof Nip86NetworkError) {
+        // Network/CORS error - provide helpful messaging
+        setMethodsError(
+          error.isCorsLikely
+            ? "Cannot connect to relay API. The relay may not support NIP-86, or CORS is blocking the request."
+            : error.message,
+        );
       } else {
         setMethodsError(
           error instanceof Error ? error.message : "Failed to fetch methods",

src/lib/nip86-client.ts

@@ -52,6 +52,17 @@ export class Nip86AuthError extends Nip86Error {
   }
 }
 
+/** NIP-86 network/CORS error */
+export class Nip86NetworkError extends Nip86Error {
+  constructor(
+    message: string = "Network error",
+    public readonly isCorsLikely: boolean = false,
+  ) {
+    super(message);
+    this.name = "Nip86NetworkError";
+  }
+}
+
 /**
  * NIP-86 Relay Management API Client
  *
@@ -93,14 +104,34 @@ export class Nip86Client {
       this.sign,
     );
 
-    const response = await fetch(this.httpUrl, {
-      method: "POST",
-      headers: {
-        "Content-Type": CONTENT_TYPE,
-        Authorization: authHeader,
-      },
-      body,
-    });
+    let response: Response;
+    try {
+      response = await fetch(this.httpUrl, {
+        method: "POST",
+        headers: {
+          "Content-Type": CONTENT_TYPE,
+          Authorization: authHeader,
+        },
+        body,
+      });
+    } catch (error) {
+      // Network errors (including CORS) throw TypeError with "Failed to fetch"
+      const message =
+        error instanceof Error ? error.message : "Network request failed";
+
+      // "Failed to fetch" is the typical CORS or network error message
+      const isCorsLikely =
+        message.toLowerCase().includes("failed to fetch") ||
+        message.toLowerCase().includes("network") ||
+        message.toLowerCase().includes("cors");
+
+      throw new Nip86NetworkError(
+        isCorsLikely
+          ? "Network error - relay may not support CORS or NIP-86"
+          : message,
+        isCorsLikely,
+      );
+    }
 
     if (response.status === 401) {
       throw new Nip86AuthError();