refactor: simplify jt808 daily mileage strategy

docs/superpowers/specs/2026-06-23-gb32960-production-readiness-design.md

@@ -337,23 +337,18 @@ Validation:
 
 ### Daily Mileage
 
-Preferred:
-
-```text
-dailyMileage = today.lastTotalMileage - previousDay.lastTotalMileage
-```
-
-Fallback:
+JT808 daily mileage uses the GPS total mileage reported in location additional
+information. The first valid sample of the local day is the baseline and the
+latest valid total mileage rewrites the same metric row.
 
 ```text
 dailyMileage = today.lastTotalMileage - today.firstTotalMileage
+calculationMethod = JT808_TOTAL_MILEAGE_DIFF
 ```
 
-Quality:
-
-- `PREVIOUS_DAY_BASELINE` when previous day baseline exists;
-- `INTRADAY_DELTA` when only same-day baseline exists;
-- `INSUFFICIENT_DATA` when neither is reliable.
+The result is stored in `vehicle_stat_metric` with
+`metric_key=daily_mileage_km`. There is no JT808-specific daily mileage table,
+no Redis mileage state, and no previous-day baseline calculation.
 
 ### Daily Power Consumption
 

modules/services/vehicle-stat-service/src/main/java/com/lingniu/ingest/vehiclestat/DailyMileageStrategy.java

@@ -8,9 +8,6 @@ public enum DailyMileageStrategy {
             return JT808_TOTAL_MILEAGE_DIFF;
         }
         String normalized = value.trim();
-        if ("CURRENT_LAST_MINUS_PREVIOUS_LAST".equals(normalized)) {
-            return JT808_TOTAL_MILEAGE_DIFF;
-        }
         return DailyMileageStrategy.valueOf(normalized);
     }
 }

modules/services/vehicle-stat-service/src/test/java/com/lingniu/ingest/vehiclestat/JdbcVehicleStatMetricRepositoryTest.java

@@ -7,6 +7,7 @@ import org.springframework.jdbc.datasource.DriverManagerDataSource;
 import java.time.LocalDate;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 class JdbcVehicleStatMetricRepositoryTest {
 
@@ -147,7 +148,7 @@ class JdbcVehicleStatMetricRepositoryTest {
     }
 
     @Test
-    void readsLegacyCalculationMethodAsTotalMileageDifference() {
+    void rejectsLegacyPreviousDayCalculationMethod() {
         JdbcTemplate jdbcTemplate = new JdbcTemplate(new DriverManagerDataSource(
                 "jdbc:h2:mem:vehicle_stat_metric_legacy;MODE=MySQL;DATABASE_TO_LOWER=TRUE;DB_CLOSE_DELAY=-1",
                 "sa",
@@ -159,10 +160,8 @@ class JdbcVehicleStatMetricRepositoryTest {
                 VALUES ('VIN001', DATE '2026-06-30', 'daily_mileage_km', 8.5, 'km', 'CURRENT_LAST_MINUS_PREVIOUS_LAST')
                 """);
 
-        assertThat(repository.findDailyStat("VIN001", LocalDate.of(2026, 6, 30)))
-                .isPresent()
-                .get()
-                .extracting(VehicleDailyStatResult::dailyMileageStrategy)
-                .isEqualTo(DailyMileageStrategy.JT808_TOTAL_MILEAGE_DIFF);
+        assertThatThrownBy(() -> repository.findDailyStat("VIN001", LocalDate.of(2026, 6, 30)))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessageContaining("CURRENT_LAST_MINUS_PREVIOUS_LAST");
     }
 }