fix: 彻底移除MT批处理，qwen-mt模型会破坏所有文本分隔符

日志证实: \n\n---\n\n分隔符被MT模型破坏率82%(28/34批次)
MT模型逐条翻译是唯一可靠方案，无法批处理

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docutranslate/agents/segments_agent.py

@@ -182,47 +182,6 @@ class SegmentsTranslateAgent(Agent):
             logger.error(f"原始prompt也不是有效的json格式: {original_segments}")
             return {"error": f"{original_segments}"}
 
-    MT_BATCH_SEP = "\n\n---\n\n"
-
-    def _batch_segments_for_mt(self, segments: list[str], chunk_size: int) -> tuple[list[str], list[list[int]]]:
-        """将 segments 按字符数分批，用分隔符连接。返回(批文本列表, 每批的索引列表)。"""
-        batches = []
-        index_groups = []
-        current_parts = []
-        current_indices = []
-        current_size = 0
-        sep = self.MT_BATCH_SEP
-        sep_size = len(sep.encode('utf-8'))
-
-        for i, seg in enumerate(segments):
-            seg_size = len(seg.encode('utf-8'))
-            add_size = (sep_size if current_parts else 0) + seg_size
-
-            if current_parts and current_size + add_size > chunk_size:
-                batches.append(sep.join(current_parts))
-                index_groups.append(current_indices)
-                current_parts = [seg]
-                current_indices = [i]
-                current_size = seg_size
-            else:
-                current_parts.append(seg)
-                current_indices.append(i)
-                current_size += add_size
-
-        if current_parts:
-            batches.append(sep.join(current_parts))
-            index_groups.append(current_indices)
-
-        return batches, index_groups
-
-    def _mt_batch_result_handler(self, result: str, origin_prompt: str, logger: Logger) -> list[str]:
-        """MT batch: 按分隔符拆分翻译结果。"""
-        return [p.strip() for p in result.strip().split(self.MT_BATCH_SEP)]
-
-    def _mt_batch_error_handler(self, origin_prompt: str, logger: Logger) -> list[str]:
-        """MT batch error: 返回原文各段。"""
-        return [p.strip() for p in origin_prompt.split(self.MT_BATCH_SEP)]
-
     def _mt_individual_result_handler(self, result: str, origin_prompt: str, logger: Logger) -> str:
         """MT individual: 直接返回翻译结果。"""
         return result.strip()
@@ -276,22 +235,15 @@ class SegmentsTranslateAgent(Agent):
 
     def send_segments(self, segments: list[str], chunk_size: int) -> list[str]:
         if self.is_mt_mode:
+            # MT models (qwen-mt-*) destroy ALL text separators — batching is impossible.
+            # Each segment must be sent individually for 100% reliable 1:1 mapping.
             if not segments:
                 return []
-            batch_texts, batch_indices = self._batch_segments_for_mt(segments, chunk_size)
-            batch_results = super().send_prompts(
-                prompts=batch_texts,
-                result_handler=self._mt_batch_result_handler,
-                error_result_handler=self._mt_batch_error_handler,
+            return super().send_prompts(
+                prompts=segments,
+                result_handler=self._mt_individual_result_handler,
+                error_result_handler=self._mt_individual_error_handler,
             )
-            all_translated, mismatched = self._apply_mt_batch_results(
-                segments, batch_results, batch_indices
-            )
-            if mismatched:
-                retranslated = self._retranslate_mismatched(segments, mismatched)
-                for idx, trans in retranslated.items():
-                    all_translated[idx] = trans
-            return all_translated
 
         # Non-MT mode: JSON batch translation
         indexed_originals, chunks, merged_indices_list = segments2json_chunks(segments, chunk_size)
@@ -331,26 +283,14 @@ class SegmentsTranslateAgent(Agent):
 
     async def send_segments_async(self, segments: list[str], chunk_size: int) -> list[str]:
         if self.is_mt_mode:
+            # MT models destroy ALL text separators — each segment must be sent individually.
             if not segments:
                 return []
-            batch_texts, batch_indices = await asyncio.to_thread(
-                self._batch_segments_for_mt, segments, chunk_size
+            return await super().send_prompts_async(
+                prompts=segments,
+                result_handler=self._mt_individual_result_handler,
+                error_result_handler=self._mt_individual_error_handler,
             )
-            batch_results = await super().send_prompts_async(
-                prompts=batch_texts,
-                result_handler=self._mt_batch_result_handler,
-                error_result_handler=self._mt_batch_error_handler,
-            )
-            all_translated, mismatched = self._apply_mt_batch_results(
-                segments, batch_results, batch_indices
-            )
-            if mismatched:
-                retranslated = await asyncio.to_thread(
-                    self._retranslate_mismatched, segments, mismatched
-                )
-                for idx, trans in retranslated.items():
-                    all_translated[idx] = trans
-            return all_translated
 
         # Non-MT mode: JSON batch translation
         indexed_originals, chunks, merged_indices_list = await asyncio.to_thread(segments2json_chunks, segments,