Align instance dashboard with hub snapshot+SSE pattern.

Background poll builds a memory snapshot; the page reads snapshot and refreshes on SSE instead of hitting heavy exchange APIs on each load.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_instance_dashboard_cache.py

@@ -0,0 +1,48 @@
+"""instance_dashboard_cache 单元测试."""
+from __future__ import annotations
+
+import time
+import unittest
+
+from lib.instance.instance_dashboard_cache import InstanceDashboardStore
+
+
+class TestInstanceDashboardStore(unittest.TestCase):
+    def test_snapshot_before_ready(self):
+        store = InstanceDashboardStore()
+        snap = store.snapshot_dict()
+        self.assertFalse(snap["ok"])
+        self.assertIn("尚未就绪", snap["msg"])
+
+    def test_aggregate_and_snapshot(self):
+        store = InstanceDashboardStore()
+        calls = {"n": 0}
+
+        def build():
+            calls["n"] += 1
+            return {"ok": True, "updated_at": "t1", "orders": {"count": 0, "items": []}}
+
+        store.start(build)
+        deadline = time.time() + 3
+        while time.time() < deadline:
+            snap = store.snapshot_dict()
+            if snap.get("ok") and snap.get("dashboard_version", 0) >= 1:
+                break
+            time.sleep(0.05)
+        snap = store.snapshot_dict()
+        self.assertTrue(snap["ok"])
+        self.assertGreaterEqual(snap["dashboard_version"], 1)
+        self.assertGreaterEqual(calls["n"], 1)
+        store.request_refresh()
+        ver0 = snap["dashboard_version"]
+        deadline = time.time() + 3
+        while time.time() < deadline:
+            if store.snapshot_dict().get("dashboard_version", 0) > ver0:
+                break
+            time.sleep(0.05)
+        self.assertGreater(store.snapshot_dict()["dashboard_version"], ver0)
+        store.stop()
+
+
+if __name__ == "__main__":
+    unittest.main()