fix: map_fields empty-retry + correction prompt field_N guidance

- map_fields: retry with simplified prompt on empty LLM response
- correction.md: add explicit guidance for undeclared field_N errors
  (add <field> declarations + try OCR name replacement)
- MAX_RETRY=5 now effective (was overridden by .env:3)

agent/nodes.py

@@ -754,8 +754,20 @@ def map_fields(state: AgentState) -> Dict:
     )
     prev_jrxml = state.get("current_jrxml", "")
     full_text = _generate_with_continuation(llm, prompt, writer, "map_fields")
+    # 空响应重试：有时 LLM 第一轮不输出，换个方式再试一次
     if not full_text.strip():
-        _node_log.error("map_fields LLM 返回空响应，保留占位字段版本")
+        _node_log.warning("map_fields 第一轮返回空响应，尝试简化 prompt 重试")
+        retry_prompt = (
+            "请将以下 JRXML 中的占位字段名 $F{field_1}, $F{field_2}, ... 替换为 OCR 提取的真实字段名。\n"
+            "规则：根据列顺序映射——$F{field_1} 对应第1列，$F{field_2} 对应第2列，以此类推。\n"
+            "同时更新 <field name=\"...\"> 声明和所有 $F{...} 引用。\n"
+            "只输出完整 JRXML，不要解释。\n\n"
+            f"OCR 字段：\n{fields_text}\n\n"
+            f"JRXML：\n{prev_jrxml}"
+        )
+        full_text = _generate_with_continuation(llm, retry_prompt, writer, "map_fields")
+    if not full_text.strip():
+        _node_log.error("map_fields LLM 重试后仍返回空响应，保留占位字段版本")
         return state
     jrxml = _extract_jrxml(full_text)
     if len(jrxml.strip()) < 200: