fix: 分块大小减至5MB + Edge端chunk_size变更自动清理 + 断点续传防护

NAS dispatcher:
- CHUNK_SIZE 10MB→5MB（~1Mbps上行带宽下可靠传输）
- chunk上传timeout (30,120)→(60,180)（增加连接和读取余量）
- _query_uploaded_chunks 返回 (set, edge_total) 元组
- expected_total != edge_total 时跳过断点续传（防止chunk_size变更导致文件损坏）

Edge api_gateway:
- upload_chunk 检测 total_chunks 变更，自动清理旧分块
- 防止不同chunk_size的旧分块与新分块混合导致assemble后文件损坏

fam-core/src/fam_core/dispatcher/dispatcher.py

@@ -27,7 +27,7 @@ from .. import db_layer
 
 logger = setup_logger('fam-core.dispatcher')
 
-CHUNK_SIZE = 10 * 1024 * 1024        # 10MB per chunk (smaller = fewer timeouts)
+CHUNK_SIZE = 5 * 1024 * 1024         # 5MB per chunk (reliable at ~1Mbps upload)
 CHUNK_THRESHOLD = 20 * 1024 * 1024  # files > 20MB use chunked upload
 MAX_CHUNK_RETRIES = 3
 
@@ -145,8 +145,13 @@ class Dispatcher:
         logger.error(f"[task_id={task_id}] Edge 返回异常状态码: {resp.status_code}")
         self._schedule_retry(task)
 
-    def _query_uploaded_chunks(self, task_id):
-        """查询 Edge 端已上传分块列表"""
+    def _query_uploaded_chunks(self, task_id, expected_total=None):
+        """查询 Edge 端已上传分块列表
+
+        返回 (uploaded_set, edge_total_chunks)。
+        如果 expected_total 与 edge_total 不匹配（chunk_size 变更），
+        返回空集让 Edge 自动清理旧分块。
+        """
         try:
             resp = requests.get(
                 self.chunks_query_url,
@@ -154,10 +159,17 @@ class Dispatcher:
                 timeout=(30, 15)
             )
             if resp.status_code == 200:
-                return set(resp.json().get('uploaded_chunks', []))
+                data = resp.json()
+                uploaded = set(data.get('uploaded_chunks', []))
+                edge_total = data.get('total_chunks', 0)
+                if expected_total and edge_total and edge_total != expected_total:
+                    logger.warning(f"[task_id={task_id}] Edge total_chunks={edge_total} "
+                                   f"≠ expected={expected_total}（chunk_size 已变更），从头上传")
+                    return set(), edge_total
+                return uploaded, edge_total
         except requests.RequestException:
             pass
-        return set()
+        return set(), 0
 
     def _dispatch_chunked(self, task, payload, video_path, file_size):
         """大文件分块上传 + 断点续传
@@ -171,7 +183,7 @@ class Dispatcher:
         filename = os.path.basename(video_path)
 
         # 1. 查询已上传分块（断点续传）
-        uploaded_set = self._query_uploaded_chunks(task_id)
+        uploaded_set, edge_total = self._query_uploaded_chunks(task_id, expected_total=total_chunks)
         if uploaded_set:
             logger.info(f"[task_id={task_id}] 断点续传: 已有 {len(uploaded_set)}/{total_chunks} 块")
 
@@ -198,7 +210,7 @@ class Dispatcher:
                                     'filename': filename,
                                 },
                                 files={'chunk': (f'chunk_{idx}', io.BytesIO(chunk_data))},
-                                timeout=(30, 120)
+                                timeout=(60, 180)
                             )
                             if cresp.status_code == 200:
                                 success = True
@@ -211,7 +223,7 @@ class Dispatcher:
                             time.sleep(5 * (attempt + 1))
 
                     if not success:
-                        uploaded_now = self._query_uploaded_chunks(task_id)
+                        uploaded_now, _ = self._query_uploaded_chunks(task_id)
                         if idx in uploaded_now:
                             logger.info(f"[task_id={task_id}] 分块 {idx} 虽超时但 Edge 已收到，继续下一块")
                             uploaded_set.add(idx)

fam-edge/src/fam_edge/api_gateway/api_gateway.py

@@ -168,11 +168,26 @@ def upload_chunk():
     chunk_path = os.path.join(d, f"chunk_{chunk_index:04d}")
 
     try:
+        # 检查 total_chunks 是否变化（chunk_size 变更导致），自动清理旧分块
+        meta_path = os.path.join(d, "meta.json")
+        if total_chunks and os.path.exists(meta_path):
+            import json
+            try:
+                with open(meta_path) as mf:
+                    old_meta = json.load(mf)
+                if old_meta.get('total_chunks') and old_meta['total_chunks'] != total_chunks:
+                    logger.warning(f"[task_id={task_id}] total_chunks 变更 "
+                                   f"({old_meta['total_chunks']}→{total_chunks})，清理旧分块")
+                    for fn in os.listdir(d):
+                        if fn.startswith('chunk_'):
+                            os.remove(os.path.join(d, fn))
+            except (json.JSONDecodeError, IOError):
+                pass
+
         chunk_file.save(chunk_path)
         size_kb = os.path.getsize(chunk_path) / 1024
 
-        # 写元数据（首次上传时）
-        meta_path = os.path.join(d, "meta.json")
+        # 写/更新元数据
         if not os.path.exists(meta_path):
             import json
             meta = {"filename": filename, "total_chunks": total_chunks}