fix: transplant PG init backfill rollback scope + audit-loop state upsert registration (code-to10 v2, from 854f810)

- db: translate INSERT OR IGNORE ... SELECT to ON CONFLICT DO NOTHING;
  register task_audit_loop_state (task_id) in _OR_REPLACE_PK (direct port).
- server: _backfill_default_quotas uses SAVEPOINT containment, no longer
  commits the caller's transaction (direct port; callers are init_db only).
- worker: NOT ported — integration _coord_child_rows has no column-fallback
  retry loop, so the InFailedSqlTransaction cascade site does not exist here.
- tests: rewritten for the integration base (no cloud.audit_loop /
  _coord_audit_loop_merge here); real-PG cases skip without DSN/driver.

(cherry picked from commit 79e6843610fcd275af874e7b4afc57af7ffa579e)

cloud/server.py

@@ -1536,8 +1536,28 @@ def _backfill_default_quotas(conn):
 
     只补“users 里有、user_quotas 里无”的用户，已有行（含
     管理员显式设为 NULL 的不限额行）一律不动。返回补写行数。
+
+    失败只回滚到保存点，绝不回滚调用方的整个事务：init_db
+    里 migrate 的 ALTER 与它同事务，旧版 except 里整事务
+    rollback 会把 ALTER 一并丢掉（2026-10-31 新鲜 PG 库实测：
+    init 后 tasks 缺 paused_by_user / interrupted_reason，合流
+    随后在 PG“语句失败即 abort 整个事务”的语义下连环报
+    InFailedSqlTransaction）。成功时也不再由本函数提交，提交
+    由调用方负责（init_db 结尾统一提交；旧版成功时提交等于
+    提前提交 init 的全部 DDL，改后 init 恢复原子性）。调用方
+    只有 init_db 两处（均以提交收尾），改动不影响其它路径。
+    保存点在 SQLite 与 PG 下都支持；保存点本身建不起来时
+    （如连接已处 abort 态）退化为整事务 rollback 再返回 0。
     """
     _ensure_quotas_table(conn)
+    try:
+        conn.execute("SAVEPOINT backfill_default_quotas")
+    except Exception:
+        try:
+            conn.rollback()
+        except Exception:
+            pass
+        return 0
     try:
         cur = conn.execute(
             "INSERT OR IGNORE INTO user_quotas(user_id,"
@@ -1546,13 +1566,17 @@ def _backfill_default_quotas(conn):
             " LEFT JOIN user_quotas q ON q.user_id = u.id"
             " WHERE q.user_id IS NULL",
             (_default_quota_usd_micros(), time.time()))
-        conn.commit()
+        conn.execute("RELEASE SAVEPOINT backfill_default_quotas")
         return cur.rowcount or 0
     except Exception:
         try:
-            conn.rollback()
+            conn.execute("ROLLBACK TO SAVEPOINT backfill_default_quotas")
+            conn.execute("RELEASE SAVEPOINT backfill_default_quotas")
         except Exception:
-            pass
+            try:
+                conn.rollback()
+            except Exception:
+                pass
         return 0