diff --git a/app/store.py b/app/store.py
index 6d921bb..2c75151 100644
--- a/app/store.py
+++ b/app/store.py
@@ -1,13 +1,13 @@
 import asyncio
 from dataclasses import dataclass
-from datetime import UTC, datetime
+from datetime import datetime, timezone
 from uuid import UUID, uuid4
 
-from app.models import Monitor, MonitorCreate, MonitorUpdate, StatusSnapshot
+from app.models import CheckStatus, Monitor, MonitorCreate, MonitorUpdate
 
 
-@dataclass
-class _Record:
+@dataclass(frozen=True)
+class Snapshot:
     monitor: Monitor
     revision: int
 
@@ -15,61 +15,54 @@ class _Record:
 class MonitorStore:
     def __init__(self) -> None:
         self._lock = asyncio.Lock()
-        self._records: dict[UUID, _Record] = {}
+        self._items: dict[UUID, tuple[Monitor, int]] = {}
 
     async def create(self, data: MonitorCreate) -> Monitor:
-        now = datetime.now(UTC)
-        monitor = Monitor(
-            id=uuid4(), name=data.name, url=data.url, created_at=now,
-            updated_at=now, status=StatusSnapshot(),
-        )
+        now = datetime.now(timezone.utc)
+        item = Monitor(id=uuid4(), name=data.name, url=data.url, created_at=now,
+                       updated_at=now, status=CheckStatus())
         async with self._lock:
-            self._records[monitor.id] = _Record(monitor, 0)
-        return monitor.model_copy(deep=True)
+            self._items[item.id] = (item, 1)
+        return item.model_copy(deep=True)
 
     async def list(self) -> list[Monitor]:
         async with self._lock:
-            values = [item.monitor for item in self._records.values()]
-            return [value.model_copy(deep=True) for value in values]
+            values = [item.model_copy(deep=True) for item, _ in self._items.values()]
+        return sorted(values, key=lambda item: (item.created_at, str(item.id)))
 
-    async def get(self, monitor_id: UUID) -> Monitor | None:
+    async def snapshot(self, monitor_id: UUID) -> Snapshot | None:
         async with self._lock:
-            record = self._records.get(monitor_id)
-            return record.monitor.model_copy(deep=True) if record else None
+            stored = self._items.get(monitor_id)
+            if stored is None:
+                return None
+            item, revision = stored
+            return Snapshot(item.model_copy(deep=True), revision)
 
     async def update(self, monitor_id: UUID, data: MonitorUpdate) -> Monitor | None:
         async with self._lock:
-            record = self._records.get(monitor_id)
-            if not record:
+            stored = self._items.get(monitor_id)
+            if stored is None:
                 return None
-            url_changed = record.monitor.url != data.url
-            status = StatusSnapshot() if url_changed else record.monitor.status
-            record.monitor = record.monitor.model_copy(update={
-                "name": data.name, "url": data.url, "updated_at": datetime.now(UTC),
-                "status": status,
-            })
-            record.revision += 1
-            return record.monitor.model_copy(deep=True)
+            item, revision = stored
+            changes = data.model_dump(exclude_none=True)
+            if "url" in changes:
+                changes["status"] = CheckStatus()
+            changes["updated_at"] = datetime.now(timezone.utc)
+            updated = item.model_copy(update=changes)
+            self._items[monitor_id] = (updated, revision + 1)
+            return updated.model_copy(deep=True)
 
     async def delete(self, monitor_id: UUID) -> bool:
         async with self._lock:
-            return self._records.pop(monitor_id, None) is not None
+            return self._items.pop(monitor_id, None) is not None
 
-    async def begin_check(self, monitor_id: UUID) -> tuple[Monitor, int] | None:
+    async def apply_status(self, monitor_id: UUID, revision: int,
+                           status: CheckStatus) -> bool:
         async with self._lock:
-            record = self._records.get(monitor_id)
-            if not record:
-                return None
-            return record.monitor.model_copy(deep=True), record.revision
-
-    async def finish_check(
-        self, monitor_id: UUID, revision: int, status: StatusSnapshot,
-    ) -> bool:
-        async with self._lock:
-            record = self._records.get(monitor_id)
-            if not record or record.revision != revision:
+            stored = self._items.get(monitor_id)
+            if stored is None or stored[1] != revision:
                 return False
-            record.monitor = record.monitor.model_copy(update={
-                "status": status, "updated_at": datetime.now(UTC),
-            })
+            item, current_revision = stored
+            updated = item.model_copy(update={"status": status})
+            self._items[monitor_id] = (updated, current_revision)
             return True