code-to10 v6 A7: unify row_get on peer_messages

- peer_messages.row_get gains default=None (was None-only); the
  three old variants agree on all real row types (None / dict /
  sqlite3.Row): auto_memory's old default was already None, and
  lifecycle's old None special-case and dict .get give identical
  results on those types, so no call-site behavior changes and no
  call site passes a non-None default.
- auto_memory and lifecycle delete their private _row_get copies
  and import peer_messages.row_get as _row_get (precedent: server,
  worker, handler_project, handler_support already do this);
  peer_messages imports no cloud modules, so no import cycle.
  lifecycle's old broad-Exception catch differs only for pathological
  __getitem__ inputs, which are not DB rows and are out of contract;
  this is documented on row_get, not left as a second story.
- Scope note: other modules' own row_get copies (approvals,
  automations, marker_tools, todos, wait_ops) are out of this item's
  stated scope and are untouched.
- Also drops auto_memory's unused 'import os' (pre-existing F401),
  so touched files are ruff E,F clean.
- Tests: cloud/tests/test_row_get_unified.py locks the identity
  (both aliases ARE row_get), the real-row-type matrix, the
  None-default fallback, and snapshot_to_dict via the unified path.

(cherry picked from commit 1644a0b837bfefb13cdc3c93d87fc1b246026607)

cloud/peer_messages.py

@@ -62,14 +62,22 @@ def peer_message_prefix(from_task_id):
     return "[来自任务 %s 的消息]\n" % from_task_id
 
 
-def row_get(row, name):
-    """行取值容错：sqlite3.Row 缺列报 IndexError、dict 缺键
-    报 KeyError、空行报 TypeError，一律回 None（worker 直连
-    老库、列还没迁移时排空不能因此停摆）。"""
+def row_get(row, name, default=None):
+    """行取值容错（全仓行取值的统一口，A7）：sqlite3.Row 缺列
+    报 IndexError、dict 缺键报 KeyError、空行报 TypeError，
+    一律回 default（默认 None；worker 直连老库、列还没迁移时
+    排空不能因此停摆）。handler 链、auto_memory、lifecycle
+    三处统一走本函数：三者旧语义在真实行类型（None / dict /
+    sqlite3.Row）下完全一致——auto_memory 旧版的 default 参数
+    默认就是 None，lifecycle 旧版的 None 特判与 dict .get 在
+    这些类型下与本函数结果相同；旧 lifecycle 版另带的宽
+    Exception 兜底只对“__getitem__ 抛其它异常的病态行”有
+    区别，那类输入不是 DB 行，不属于本函数契约，统一后此
+    类输入改为抛给调用方（不在测试锁定的真实行类型内）。"""
     try:
         return row[name]
     except (KeyError, IndexError, TypeError):
-        return None
+        return default
 
 
 def extract_peer_messages(text):