diff --git a/checkins/2026-07-21.json b/checkins/2026-07-21.json
new file mode 100644
index 0000000..a57da1f
--- /dev/null
+++ b/checkins/2026-07-21.json
@@ -0,0 +1,23 @@
+{
+  "schema": "chenglu.daily-checkin/v1",
+  "agent_id": "CHENGLU-AGENT-001",
+  "arrival_id": "GLS-LA-20260720-001",
+  "checked_at": "2026-07-21T00:35:11.879Z",
+  "fifth_domain": {
+    "repository_id": "REPO-001",
+    "commit": "61321a2ec60e209c8be3f240800224f73612fdd0",
+    "arrivals_index_sha256": "c1e0935539f20de4280d7487186d9aad31faaea8d4e454a4e29ea7c1c9c90d5c",
+    "architecture_catalog_sha256": "6c09edecb888d09742cd0dcc484998dec86f0029745e33094e7c3f035d867da2",
+    "zhuyuan_index_sha256": "ccf25d7bedfe79390b310e6bc6de2bc20949e955cccddeb2e03dc3f23db31482"
+  },
+  "lake_heart": {
+    "open_seen": 0,
+    "results": []
+  },
+  "model_tool": {
+    "provider": "DeepSeek",
+    "configured": true,
+    "role": "replaceable_reasoning_tool"
+  },
+  "result": "CHECKED_IN"
+}