fix(rectification): surface pricing failures and persist opening question

frontend/src/lib/rectification-agentic/v9/stream-mapping.ts

@@ -18,7 +18,6 @@ import {
   type RectificationActivityChangedEvent,
   type RectificationActivityEvent,
   type RectificationChoiceAppliedEvent,
-  type PublicRectificationActivity,
   type PublicRectificationMethod,
   type PublicRectificationPhase,
   type PublicRectificationTool,
@@ -36,6 +35,7 @@ export type PublicPhaseStreamEvent = Readonly<{
 
 export type PublicErrorCode =
   | "billing_denied"
+  | "billing_unavailable"
   | "skill_identity_unverifiable"
   | "skill_identity_missing"
   | "skill_identity_mismatch"
@@ -284,6 +284,7 @@ export function safePublicEvent(value: unknown): PublicStreamEvent | null {
   if (event.type === "error") {
     const codes = new Set<PublicErrorCode>([
       "billing_denied",
+      "billing_unavailable",
       "skill_identity_unverifiable",
       "skill_identity_missing",
       "skill_identity_mismatch",