fix(providers): surface clear arrearage warning on quota/billing errors (#3006)

nanobot/agent/runner.py

@@ -53,6 +53,10 @@ from nanobot.utils.runtime import (
 )
 
 _DEFAULT_ERROR_MESSAGE = "Sorry, I encountered an error calling the AI model."
+_ARREARAGE_ERROR_MESSAGE = (
+    "The AI provider rejected the request because the API key is out of quota or the "
+    "account is in arrears. Please top up / check the billing status of your API key and try again."
+)
 _PERSISTED_MODEL_ERROR_PLACEHOLDER = "[Assistant reply unavailable due to model error.]"
 _MAX_EMPTY_RETRIES = 2
 _MAX_LENGTH_RECOVERIES = 3
@@ -504,7 +508,10 @@ class AgentRunner:
                 continue
 
             if response.finish_reason == "error":
-                final_content = clean or spec.error_message or _DEFAULT_ERROR_MESSAGE
+                if LLMProvider.is_arrearage_response(response):
+                    final_content = _ARREARAGE_ERROR_MESSAGE
+                else:
+                    final_content = clean or spec.error_message or _DEFAULT_ERROR_MESSAGE
                 stop_reason = "error"
                 error = final_content
                 self._append_model_error_placeholder(messages)

nanobot/providers/base.py

@@ -315,6 +315,29 @@ class LLMProvider(ABC):
 
         return cls._is_transient_error(response.content)
 
+    @classmethod
+    def is_arrearage_response(cls, response: LLMResponse) -> bool:
+        """Detect API-key arrearage / quota / billing errors that won't clear on retry.
+
+        These surface as HTTP 402 or as billing semantic tokens (e.g.
+        ``insufficient_quota``, ``payment_required``); reuses the same token and
+        text markers the 429 retry policy treats as non-retryable.
+        """
+        if response.error_status_code is not None and int(response.error_status_code) == 402:
+            return True
+
+        type_token = cls._normalize_error_token(response.error_type)
+        code_token = cls._normalize_error_token(response.error_code)
+        if any(
+            token in cls._NON_RETRYABLE_429_ERROR_TOKENS
+            for token in (type_token, code_token)
+            if token is not None
+        ):
+            return True
+
+        content = (response.content or "").lower()
+        return any(marker in content for marker in cls._NON_RETRYABLE_429_TEXT_MARKERS)
+
     @staticmethod
     def _normalize_error_token(value: Any) -> str | None:
         if value is None: