fix(gemini): Robust error handling for empty streaming responses

PROBLEMA (Screenshot 2025-11-24 20-07-30):
  ❌ Error: 'response.text' quick accessor requires valid Part
  ❌ finish_reason=1 (STOP) but no text returned
  ❌ Frame budget exceeded: 6255.3ms

CAUSA-RAIZ:
  - Gemini retorna chunks sem .text (blocked by safety filters)
  - Código tentava acessar chunk.text cegamente
  - AttributeError causava crash do streaming

SOLUÇÃO:
  1. Verificar hasattr(chunk, 'text') ANTES de acessar
  2. Fallback para chunk.parts se .text não existir
  3. Try-catch individual por chunk (não quebra todo stream)
  4. Log de finish_reason quando detectado
  5. Mensagem clara se zero chunks recebidos

Mudanças:
  • Wrapped chunk.text access em try-except
  • Added hasattr checks
  • Fallback: chunk.parts[].text
  • Counter: chunks_received
  • Fallback message se nenhum chunk válido

Benefícios:
  ✅ Streaming não crasha mais em respostas vazias
  ✅ Logs claros de por que falhou
  ✅ Mensagem informativa ao usuário
  ✅ Graceful degradation

Constitutional Compliance:
  ✅ P1 (Completeness): Error handling completo
  ✅ P3 (Critical Skepticism): Não assume chunk.text existe
  ✅ P6 (Efficiency): Previne crash = economiza tokens

Issue: #GEMINI-STREAMING-EMPTY-RESPONSE

Author: JuanCS-Dev

qwen_dev_cli/core/providers/gemini.py

@@ -220,10 +220,32 @@ def _stream():
             loop = asyncio.get_event_loop()
             response = await loop.run_in_executor(None, _stream)
 
+            chunks_received = 0
             for chunk in response:
-                if chunk.text:
-                    yield chunk.text
+                # Check if chunk has text before accessing
+                try:
+                    if hasattr(chunk, 'text') and chunk.text:
+                        yield chunk.text
+                        chunks_received += 1
+                    elif hasattr(chunk, 'parts') and chunk.parts:
+                        # Fallback: try to get text from parts
+                        for part in chunk.parts:
+                            if hasattr(part, 'text') and part.text:
+                                yield part.text
+                                chunks_received += 1
+                except Exception as chunk_error:
+                    logger.warning(f"Error accessing chunk.text: {chunk_error}")
+                    # Check finish_reason if available
+                    if hasattr(chunk, 'finish_reason'):
+                        logger.warning(f"Chunk finish_reason: {chunk.finish_reason}")
+                    continue
+                
                 await asyncio.sleep(0)  # Yield control
+            
+            # If no chunks received, yield fallback message
+            if chunks_received == 0:
+                logger.warning("Gemini returned no text chunks (finish_reason=1, likely blocked)")
+                yield "[Gemini returned empty response - possibly blocked by safety filters]"
 
         except Exception as e:
             logger.error(f"Gemini streaming error: {e}")