Require confirmed cache usage in strict investigation tests

src/viano_bug_analysis/llm/gateway.py

@@ -88,6 +88,11 @@ class LLMGateway:
                 for tokens in (response.input_tokens, response.output_tokens, response.cached_input_tokens, response.reasoning_tokens):
                     if tokens is not None and (isinstance(tokens, bool) or not isinstance(tokens, int) or not 0 <= tokens <= 10**12):
                         raise LLMError("LLM_RESPONSE")
+                if provider.cache_required and (provider.cache_required_prompt_prefix is None
+                        or request['prompt_version'].startswith(provider.cache_required_prompt_prefix)):
+                    if (response.cached_input_tokens is None or response.cached_input_tokens <= 0
+                            or response.input_tokens is None or response.cached_input_tokens > response.input_tokens):
+                        raise LLMError('LLM_CACHE_USAGE_UNCONFIRMED')
                 encoded = json_bytes(response.document)
                 if len(encoded) > self.config.max_response_bytes:
                     raise LLMError("LLM_RESPONSE_LIMIT")
@@ -107,6 +112,12 @@ class LLMGateway:
                 LOGGER.info("LLM request succeeded provider=%s", provider.id)
                 return {"document": parse_manifest(encoded), "metadata": metadata}
             except (ProviderUnavailable, TimeoutError) as error:
+                if provider.cache_required and (provider.cache_required_prompt_prefix is None
+                        or request['prompt_version'].startswith(provider.cache_required_prompt_prefix)):
+                    required_error = LLMError('LLM_CACHE_REQUIRED',
+                        http_status=getattr(error, 'http_status', None), diagnostics=getattr(error, 'diagnostics', None))
+                    self._failure_metadata(required_error, provider, request, started, response, attempts)
+                    raise required_error from None
                 code = error.code if isinstance(error, ProviderUnavailable) else "LLM_TIMEOUT"
                 attempts.append({"provider": provider.id, "code": code})
                 http_status = getattr(error, "http_status", None)