diff --git a/backend/app/db/base.py b/backend/app/db/base.py
index f3bf306b..80e9cf93 100644
--- a/backend/app/db/base.py
+++ b/backend/app/db/base.py
@@ -318,9 +318,23 @@ def check_pgbouncer() -> None:
 
 
 def _endpoint(url: str) -> tuple[str, int]:
-    """地址连的是哪个主机端口（端口不写按 5432）。"""
+    """地址连的是哪个主机端口（端口不写按 5432）。主机名规范化：localhost、127.x.x.x、::1 都算本机回环；IP 地址按地址比
+    （::ffff:10.0.0.5 和 10.0.0.5 相同）；解析不成 IP 的按字面（小写）比，不查 DNS。"""
+    import ipaddress
+
     parsed = make_url(url)
-    return (parsed.host or "").lower(), int(parsed.port or 5432)
+    host = (parsed.host or "").strip().strip("[]").lower().rstrip(".")
+    try:
+        addr = ipaddress.ip_address(host)
+    except ValueError:
+        addr = None
+    if isinstance(addr, ipaddress.IPv6Address) and addr.ipv4_mapped is not None:
+        addr = addr.ipv4_mapped
+    if host == "localhost" or host.endswith(".localhost") or (addr is not None and addr.is_loopback):
+        host = "loopback"
+    elif addr is not None:
+        host = str(addr)
+    return host, int(parsed.port or 5432)
 
 
 async def get_session() -> AsyncIterator[AsyncSession]:
diff --git a/backend/tests/test_db_direct.py b/backend/tests/test_db_direct.py
index b7b152f8..13c52dd0 100644
--- a/backend/tests/test_db_direct.py
+++ b/backend/tests/test_db_direct.py
@@ -109,3 +109,25 @@ def test_copying_checkpoints_goes_through_the_direct_url(monkeypatch, tmp_path):
     assert seen["direct_url"] == settings.database_direct_url, "目标就是应用库：断点走它的直连地址"
     assert to_postgres.main([str(tmp_path), "postgresql://u:p@elsewhere.internal:5432/x"]) == 2
     assert seen["direct_url"] is None, "目标是别的库：不套用应用库的直连地址"
+
+
+def test_loopback_spellings_count_as_the_same_endpoint(monkeypatch):
+    """R-b12 的尾巴：localhost、127.0.0.1、::1 是同一台机器——同一个端口时照样拒绝；IP 按地址比，解析不成 IP 的按字面比。"""
+    from app.db import base
+
+    def norm(url: str) -> str:
+        return Settings(database_url=url, _env_file=None).database_url
+
+    monkeypatch.setattr(settings, "db_pgbouncer", True)
+    for app_url, direct in (("postgresql://u:p@localhost:6432/db", "postgresql://u:p@127.0.0.1:6432/db"),
+                            ("postgresql://u:p@127.0.0.1:6432/db", "postgresql://u:p@[::1]:6432/db"),
+                            ("postgresql://u:p@10.0.0.5:6432/db", "postgresql://u:p@[::ffff:10.0.0.5]:6432/db")):
+        monkeypatch.setattr(settings, "database_url", norm(app_url))
+        monkeypatch.setattr(settings, "database_direct_url", norm(direct))
+        with pytest.raises(RuntimeError, match="指着同一个地址"):
+            base.check_pgbouncer()
+    monkeypatch.setattr(settings, "database_url", norm("postgresql://u:p@localhost:6432/db"))
+    monkeypatch.setattr(settings, "database_direct_url", norm("postgresql://u:p@127.0.0.1:5432/db"))
+    base.check_pgbouncer()   # 本机另一个端口：放行
+    monkeypatch.setattr(settings, "database_direct_url", norm("postgresql://u:p@db.internal:6432/db"))
+    base.check_pgbouncer()   # 名字不同、不查 DNS：按字面算不同