fix: read naive ClickHouse datetimes as UTC in the console

src/dfe_engine/appmgmt/operations.py

@@ -20,6 +20,7 @@
 import re
 from collections.abc import Sequence
 from dataclasses import dataclass, field
+from datetime import UTC, datetime
 from pathlib import Path
 from typing import Any
 
@@ -363,9 +364,14 @@ def _last_increase(series: Sequence[tuple[float, float, float]]) -> float | None
 
 
 def _epoch(value: Any) -> float | None:
-    """Coerce a ClickHouse DateTime or numeric to a POSIX timestamp."""
+    """Coerce a ClickHouse DateTime or numeric to a POSIX timestamp.
+
+    clickhouse-connect returns naive datetimes in UTC, so a naive value is read as
+    UTC rather than the host's local time.
+    """
     if value is None:
         return None
-    if hasattr(value, "timestamp"):
-        return float(value.timestamp())
+    if isinstance(value, datetime):
+        aware = value if value.tzinfo is not None else value.replace(tzinfo=UTC)
+        return aware.timestamp()
     return float(value)

tests/unit/test_appmgmt/test_operations.py

@@ -13,6 +13,10 @@
 latest time any series MOVED, not the last time the loader reported.
 """
 
+import time
+from datetime import datetime
+from zoneinfo import ZoneInfo
+
 import pytest
 
 from dfe_engine.appmgmt.operations import (
@@ -221,6 +225,37 @@ def test_an_instance_with_telemetry_is_reporting():
     assert status.last_seen_epoch == 1757000000.0
 
 
+@pytest.fixture
+def sydney_local_time(monkeypatch: pytest.MonkeyPatch):
+    """Run with a host timezone ten or eleven hours off UTC."""
+    monkeypatch.setenv("TZ", "Australia/Sydney")
+    time.tzset()
+    yield
+    monkeypatch.undo()
+    time.tzset()
+
+
+def test_a_naive_clickhouse_datetime_is_read_as_utc_on_a_non_utc_host(
+    sydney_local_time,
+):
+    # clickhouse-connect hands back naive datetimes that are UTC.
+    naive = datetime(2025, 9, 4, 15, 33, 20)
+    ch = PerQueryClickHouse({"AS last_seen": [(naive, 12)]})
+
+    status = OperationalReader(ch, "dfe").status("dfe-loader")
+
+    assert status.last_seen_epoch == 1757000000.0
+
+
+def test_an_aware_datetime_keeps_its_own_zone(sydney_local_time):
+    aware = datetime(2025, 9, 5, 1, 33, 20, tzinfo=ZoneInfo("Australia/Sydney"))
+    ch = PerQueryClickHouse({"AS last_seen": [(aware, 12)]})
+
+    status = OperationalReader(ch, "dfe").status("dfe-loader")
+
+    assert status.last_seen_epoch == 1757000000.0
+
+
 def test_uptime_reads_the_start_time_every_dfe_app_emits():
     # A scalo-py service reports start_time_seconds and no process_start_time_seconds.
     ch = PerQueryClickHouse(