fix(llm): retry statusless mid-stream provider errors (quota/billing)

The SDK's http_status retry policy only retries errors carrying a known
HTTP status code, but quota/billing (and other provider-side) failures
often surface inside a streamed response as a bare error with no status
code, so they were failing on the first attempt. Add a statusless retry
policy to DEFAULT_MODEL_RETRY so they are retried (before any content is
streamed; user aborts are never retried), restoring the pre-SDK engine's
resilience. If the provider is genuinely exhausted, the error still
propagates and fails the scan after retries.

strix/config/models.py

@@ -10,6 +10,7 @@ from agents.models.multi_provider import MultiProvider
 from agents.retry import (
     ModelRetryBackoffSettings,
     ModelRetrySettings,
+    RetryPolicyContext,
     retry_policies,
 )
 
@@ -20,6 +21,24 @@ if TYPE_CHECKING:
     from strix.config.settings import Settings
 
 
+def _retry_statusless_provider_errors(context: RetryPolicyContext) -> bool:
+    """Retry provider errors that arrive without an HTTP status code.
+
+    Quota, billing, and other provider-side failures frequently surface *inside*
+    a streamed response as a bare error with no ``status_code`` (the transport
+    already returned ``200`` before the failure). The built-in ``http_status``
+    policy skips these because it requires a known code, so they would otherwise
+    fail on the first attempt. Retrying a statusless error (the runner still
+    refuses to replay a stream once content has been emitted, and never retries a
+    user abort) mirrors the pre-SDK engine, which retried any error lacking a
+    definitive client status code.
+    """
+    normalized = context.normalized
+    if normalized.is_abort:
+        return False
+    return normalized.status_code is None
+
+
 class StrixProvider(MultiProvider):
     """Route any non-OpenAI prefix through LiteLLM with the prefix preserved,
     so users type ``deepseek/deepseek-chat`` rather than
@@ -56,6 +75,7 @@ DEFAULT_MODEL_RETRY = ModelRetrySettings(
         retry_policies.provider_suggested(),
         retry_policies.network_error(),
         retry_policies.http_status((429, 500, 502, 503, 504)),
+        _retry_statusless_provider_errors,
     ),
 )