M8-R11: make business timezone deterministic

tests/test_deployment.py

@@ -72,6 +72,21 @@ def test_compose_uses_migration_job_before_app() -> None:
     assert dev["services"]["app"]["build"] == "."
 
 
+def test_compose_defaults_business_timezone_and_dev_inherits_it() -> None:
+    """Both production services receive an overridable Amsterdam timezone.
+
+    Compose merges service ``environment`` mappings, and the dev override does
+    not replace either mapping, so the base default applies to base+dev too.
+    """
+    base = _read_yaml("docker-compose.yml")
+    dev = _read_yaml("docker-compose.dev.yml")
+    default_tz = "${TZ:-Europe/Amsterdam}"
+
+    for service_name in ("migration", "app"):
+        assert base["services"][service_name]["environment"]["TZ"] == default_tz
+        assert "TZ" not in dev["services"].get(service_name, {}).get("environment", {})
+
+
 def test_compose_keeps_app_non_root_and_maps_minimal_warmtelink_serial_access() -> None:
     """Base Compose maps the configured device with only pyserial's required access.
 

tests/test_meter_cost_api.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 from datetime import UTC, datetime, timedelta
 from decimal import Decimal
 from unittest.mock import patch
+from zoneinfo import ZoneInfo
 
 import pytest
 from fastapi.testclient import TestClient
@@ -139,7 +140,9 @@ def test_meter_cost_summary_empty_and_recompute_csrf_window_validation(meter_cos
     ).status_code == 422
 
 
-def test_meter_cost_summary_returns_five_fixed_components_and_totals(meter_cost_client) -> None:
+def test_meter_cost_summary_returns_five_fixed_components_and_totals(
+    meter_cost_client, monkeypatch: pytest.MonkeyPatch
+) -> None:
     client, engine = meter_cost_client
     now = datetime.now(UTC)
     values = {
@@ -166,8 +169,10 @@ def test_meter_cost_summary_returns_five_fixed_components_and_totals(meter_cost_
         db.add_all((heating, water))
         db.commit()
     _login(client)
-    with patch("app.api.routes.api.meter_costs.local_now", return_value=datetime(2026, 6, 25, 2, tzinfo=UTC)):
-        response = client.get("/api/energy/meter-costs/summary?scope=thermal&start=2026-06-23T00:00:00Z&end=2026-06-24T00:00:00Z")
+    monkeypatch.setattr("app.services.timezone.local_tz", lambda: ZoneInfo("Europe/Amsterdam"))
+    response = client.get(
+        "/api/energy/meter-costs/summary?scope=thermal&start=2026-06-23T00:00:00Z&end=2026-06-24T00:00:00Z"
+    )
     assert response.status_code == 200
     body = response.json()
     assert body["heating"] == "1.000000000" and body["hot_water_heating"] == "0.8"

tests/test_timezone.py

@@ -7,7 +7,7 @@ on any CI host timezone.
 from __future__ import annotations
 
 from datetime import UTC, date, datetime
-from zoneinfo import ZoneInfo
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 import pytest
 
@@ -56,6 +56,38 @@ def test_local_tz_env_var_overrides(monkeypatch):
     monkeypatch.delenv("TZ")
 
 
+@pytest.mark.parametrize("value", [None, "", "   "])
+def test_local_tz_defaults_to_dst_aware_amsterdam(monkeypatch, value: str | None):
+    """Unset or blank TZ must use the deterministic Amsterdam business zone."""
+    if value is None:
+        monkeypatch.delenv("TZ", raising=False)
+    else:
+        monkeypatch.setenv("TZ", value)
+
+    tz = tz_mod.local_tz()
+    assert isinstance(tz, ZoneInfo)
+    assert tz.key == "Europe/Amsterdam"
+    winter = datetime(2026, 1, 15, 12, tzinfo=tz)
+    summer = datetime(2026, 7, 15, 12, tzinfo=tz)
+    assert winter.utcoffset().total_seconds() == 3600
+    assert summer.utcoffset().total_seconds() == 7200
+
+
+def test_local_tz_explicit_utc_override(monkeypatch):
+    """A non-empty TZ remains an operator-controlled override."""
+    monkeypatch.setenv("TZ", "UTC")
+    tz = tz_mod.local_tz()
+    assert isinstance(tz, ZoneInfo)
+    assert tz.key == "UTC"
+
+
+def test_local_tz_invalid_explicit_override_fails_loudly(monkeypatch):
+    """A non-empty invalid override must not silently become Amsterdam."""
+    monkeypatch.setenv("TZ", "Invalid/Timezone")
+    with pytest.raises(ZoneInfoNotFoundError):
+        tz_mod.local_tz()
+
+
 # ---------------------------------------------------------------------------
 # to_local() — conversion correctness
 # ---------------------------------------------------------------------------