fix: show clear error dialog for 403 whitelist failures

When the cloud backend returns a 403 (e.g. user not whitelisted), the
error was shown as a generic "Prompt Execution Error" with a cryptic
message. This change:

1. Adds HTTP status to PromptExecutionError so callers can distinguish
   error types
2. Catches 403 responses specifically and shows an "Access Restricted"
   dialog with the backend's actual error message

Backwards compatible: works with both the old backend message
("not authorized") and the new one ("your account is not whitelisted
for this feature" from Comfy-Org/cloud#2941).

Fixes COM-16179

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/scripts/api.ts

@@ -281,10 +281,12 @@ export interface ComfyApi extends EventTarget {
 
 export class PromptExecutionError extends Error {
   response: PromptResponse
+  status?: number
 
-  constructor(response: PromptResponse) {
+  constructor(response: PromptResponse, status?: number) {
     super('Prompt execution failed')
     this.response = response
+    this.status = status
   }
 
   override toString() {
@@ -901,7 +903,7 @@ export class ComfyApi extends EventTarget {
           }
         }
       }
-      throw new PromptExecutionError(errorResponse)
+      throw new PromptExecutionError(errorResponse, res.status)
     }
 
     return await res.json()

src/scripts/app.ts

@@ -1647,6 +1647,22 @@ export class ComfyApp {
             ) {
               // Re-scan the full graph instead of using the server's single-node response.
               rescanAndSurfaceMissingNodes(this.rootGraph)
+            } else if (
+              error instanceof PromptExecutionError &&
+              error.status === 403
+            ) {
+              // User is authenticated but not authorized (e.g. not whitelisted).
+              // Show a clear message instead of a generic error or sign-in prompt.
+              // The response may be middleware JSON {"message": "..."} which doesn't
+              // match PromptResponse schema, so access the raw parsed object.
+              const raw = error.response as Record<string, unknown>
+              const detail =
+                typeof raw.message === 'string'
+                  ? raw.message
+                  : 'Your account is not authorized for this feature.'
+              useDialogService().showErrorDialog(new Error(detail), {
+                title: 'Access Restricted'
+              })
             } else if (
               !useSettingStore().get('Comfy.RightSidePanel.ShowErrorsTab') ||
               !(error instanceof PromptExecutionError)