fix(measurement): restore JSON records into the existing singleton

src/akkudoktoreos/measurement/measurement.py

@@ -6,6 +6,7 @@ data records for measurements.
 The measurements can be added programmatically or imported from a file or JSON string.
 """
 
+import json
 from pathlib import Path
 from typing import Any, Optional
 
@@ -313,14 +314,17 @@ class Measurement(SingletonMixin, DataImportMixin, DataSequence[MeasurementDataR
             if not measurement_file_path.exists():
                 return False
             try:
-                # Validate into a temporary instance
-                loaded = self.__class__.model_validate_json(
-                    measurement_file_path.read_text(encoding="utf-8")
-                )
-
-                # Explicitly add data records to the existing singleton
-                for record in loaded.records:
+                # Measurement is a singleton; validating another Measurement
+                # returns this instance instead of restoring serialized records.
+                payload = json.loads(measurement_file_path.read_text(encoding="utf-8"))
+                # Validate the complete file before modifying the live records.
+                records = [
+                    MeasurementDataRecord.model_validate(data)
+                    for data in payload.get("records", [])
+                ]
+                for record in records:
                     await self.insert_by_datetime(record)
             except Exception as e:
                 logger.exception("Cannot load measurements")
+                return False
         return True

tests/test_measurement_file_restore.py

@@ -0,0 +1,80 @@
+"""Regression coverage for measurement persistence through the JSON fallback."""
+
+import json
+from unittest.mock import AsyncMock
+
+import pytest
+
+from akkudoktoreos.core.coreabc import get_measurement
+from akkudoktoreos.core.dataabc import DataSequence
+
+
+@pytest.fixture
+def file_measurements(config_eos, tmp_path, monkeypatch):
+    measurement = get_measurement()
+    config_eos.measurement.load_emr_keys = ["meter"]
+    config_eos.general.data_folder_path = tmp_path
+    config_eos.database.provider = None
+    measurement._db_reset_state()
+    monkeypatch.setattr(DataSequence, "save", AsyncMock(return_value=False))
+    monkeypatch.setattr(DataSequence, "load", AsyncMock(return_value=False))
+    try:
+        yield measurement
+    finally:
+        measurement._db_reset_state()
+
+
+@pytest.mark.asyncio
+async def test_json_roundtrip_restores_records_into_existing_singleton(file_measurements):
+    measurement = file_measurements
+    await measurement.update_value("2026-09-16T08:00:00Z", "meter", 123.5)
+    await measurement.update_value("2026-09-16T09:00:00Z", "meter", 124.0)
+    assert await measurement.save()
+    measurement._db_reset_state()
+
+    assert await measurement.load()
+    assert get_measurement() is measurement
+    assert [record["meter"] for record in measurement.records] == [123.5, 124.0]
+    assert [record.date_time.in_timezone("UTC").hour for record in measurement.records] == [8, 9]
+    # Reloading must update matching timestamps, without duplicating them.
+    assert await measurement.load()
+    assert len(measurement.records) == 2
+
+
+@pytest.mark.asyncio
+async def test_json_restore_preserves_other_in_memory_timestamps(file_measurements):
+    measurement = file_measurements
+    await measurement.update_value("2026-09-16T08:00:00Z", "meter", 123.5)
+    assert await measurement.save()
+    measurement._db_reset_state()
+    await measurement.update_value("2026-09-16T09:00:00Z", "meter", 124.0)
+    assert await measurement.load()
+    assert [record["meter"] for record in measurement.records] == [123.5, 124.0]
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("payload", [
+    "invalid json",
+    json.dumps({"records": [
+        {"date_time": "2026-09-16T08:00:00Z", "meter": 123.5},
+        {"date_time": "not a date", "meter": 124.0},
+    ]}),
+])
+async def test_invalid_json_does_not_partially_restore(file_measurements, payload):
+    measurement = file_measurements
+    measurement._measurement_file_path().write_text(payload, encoding="utf-8")
+    assert await measurement.load() is False
+    assert measurement.records == []
+
+
+@pytest.mark.asyncio
+async def test_database_success_does_not_read_json(file_measurements, monkeypatch):
+    measurement = file_measurements
+    measurement._measurement_file_path().write_text("invalid json", encoding="utf-8")
+    monkeypatch.setattr(DataSequence, "load", AsyncMock(return_value=True))
+    assert await measurement.load()
+
+
+@pytest.mark.asyncio
+async def test_missing_json_reports_not_loaded(file_measurements):
+    assert await file_measurements.load() is False