Add Gemini 429 retry with exponential backoff in HF fallback

Root cause: 6 parallel agents all call Gemini simultaneously when HF exhausted.
Free-tier rate limit (15 RPM) causes 429 on unlucky agents (strutturali,
consistency, financial). Previously: 429 → return empty content, no retry.

Fix: retry loop (3 attempts) with exponential backoff (2s, 4s + jitter).
Only retries on 429/rate-limit errors; non-rate errors fail immediately.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agents.py

@@ -1194,28 +1194,38 @@ e soggette a revisione post-allineamento.
                     # Gemini fallback quando tutti i modelli HF falliscono
                     _gapi_key = os.environ.get("GOOGLE_API_KEY") or os.environ.get("GEMINI_API_KEY") or GEMINI_API_KEY
                     if GENAI_AVAILABLE and _gapi_key:
-                        try:
-                            genai.configure(api_key=_gapi_key)
-                            _fallback_model = genai.GenerativeModel("gemini-2.0-flash")
-                            _response = _fallback_model.generate_content(
-                                prompt_content,
-                                generation_config=genai.types.GenerationConfig(
-                                    temperature=MODEL_CONFIG.temperature,
-                                    max_output_tokens=MODEL_CONFIG.max_tokens,
+                        citations = []
+                        for _gemini_attempt in range(3):
+                            try:
+                                if _gemini_attempt > 0:
+                                    _retry_delay = (2 ** _gemini_attempt) + __import__('random').uniform(0, 1)
+                                    logger.warning(f"Agent {self.spec.name}: Gemini retry {_gemini_attempt}/2 in {_retry_delay:.1f}s")
+                                    time.sleep(_retry_delay)
+                                genai.configure(api_key=_gapi_key)
+                                _fallback_model = genai.GenerativeModel("gemini-2.0-flash")
+                                _response = _fallback_model.generate_content(
+                                    prompt_content,
+                                    generation_config=genai.types.GenerationConfig(
+                                        temperature=MODEL_CONFIG.temperature,
+                                        max_output_tokens=MODEL_CONFIG.max_tokens,
+                                    )
                                 )
-                            )
-                            raw_content = _response.text or ""
-                            citations = []
-                            if not raw_content.strip():
-                                logger.error(f"Agent {self.spec.name}: Gemini fallback returned EMPTY content (finish_reason={getattr(_response.candidates[0] if _response.candidates else None, 'finish_reason', 'unknown')})")
-                            else:
-                                logger.info(f"Agent {self.spec.name}: Gemini fallback OK ({len(raw_content)} chars)")
-                            self.cache.set(prompt_content, raw_content)
-                        except Exception as gemini_e:
-                            logger.error(f"Agent {self.spec.name}: Gemini fallback FAILED — {type(gemini_e).__name__}: {gemini_e}")
-                            wrapped = handle_exception(gemini_e, context=f"agent_{self.spec.name}_gemini_fallback")
-                            log_exception(wrapped, context=f"agent_{self.spec.name}")
-                            return {'content': '', 'sources': [], 'unverified_claims': [], 'metadata': {'error_id': wrapped.error_id, 'error_msg': wrapped.user_message}}
+                                raw_content = _response.text or ""
+                                if not raw_content.strip():
+                                    logger.error(f"Agent {self.spec.name}: Gemini fallback returned EMPTY content (finish_reason={getattr(_response.candidates[0] if _response.candidates else None, 'finish_reason', 'unknown')})")
+                                else:
+                                    logger.info(f"Agent {self.spec.name}: Gemini fallback OK ({len(raw_content)} chars)")
+                                self.cache.set(prompt_content, raw_content)
+                                break  # success — exit retry loop
+                            except Exception as gemini_e:
+                                _is_rate_limit = '429' in str(gemini_e) or 'exhausted' in str(gemini_e).lower()
+                                if _is_rate_limit and _gemini_attempt < 2:
+                                    logger.warning(f"Agent {self.spec.name}: Gemini 429 attempt {_gemini_attempt+1}/3, will retry")
+                                    continue
+                                logger.error(f"Agent {self.spec.name}: Gemini fallback FAILED — {type(gemini_e).__name__}: {gemini_e}")
+                                wrapped = handle_exception(gemini_e, context=f"agent_{self.spec.name}_gemini_fallback")
+                                log_exception(wrapped, context=f"agent_{self.spec.name}")
+                                return {'content': '', 'sources': [], 'unverified_claims': [], 'metadata': {'error_id': wrapped.error_id, 'error_msg': wrapped.user_message}}
                     else:
                         wrapped = handle_exception(e, context=f"agent_{self.spec.name}_hf")
                         log_exception(wrapped, context=f"agent_{self.spec.name}")