Split last_upsert (persisted write) and last_refresh (run liveness) in stats

tests/test_delta.py

@@ -202,6 +202,34 @@ def test_delta_success_resets_failure_streak(env):
     assert env.cache.get_errors()["products"].consecutive == 0
 
 
+# ---------------------------------------------------------------------------
+# last_upsert (persisted write) vs last_refresh (in-memory run/liveness)
+# ---------------------------------------------------------------------------
+
+def _persisted_last_upsert(cache, table):
+    row = cache.connection.execute(
+        "SELECT last_refresh_at FROM _sqlmem_tables WHERE table_name = ?", (table,)
+    ).fetchone()
+    return row[0] if row else None
+
+
+def test_empty_delta_records_run_but_not_write(env):
+    """An empty delta cycle bumps last_refresh (liveness) but not the persisted
+    last_upsert (write time)."""
+    before = _persisted_last_upsert(env.cache, "products")
+    # Push the watermark past every source row so the next cycle returns 0 rows.
+    env.cache.set_last_synced_at("products", "2099-01-01 00:00:00")
+
+    env.refresher.refresh(env.source)
+
+    # No rows written → persisted write time unchanged.
+    assert _persisted_last_upsert(env.cache, "products") == before
+    # But the cycle ran → in-memory run time recorded (and at/after the last write).
+    runs = env.cache.get_last_runs()
+    assert runs["products"] is not None
+    assert runs["products"] >= before
+
+
 # ---------------------------------------------------------------------------
 # Engine-level: PK auto-discovery, reset, end-to-end refresh
 # ---------------------------------------------------------------------------