feat(stats): project elected mileage source

go/vehicle-gateway/internal/stats/source_mileage_test.go

@@ -81,3 +81,35 @@ func TestUpsertSourceMileageSkipsBlankSourceIP(t *testing.T) {
 		t.Fatalf("exec calls = %d, want 0", len(exec.calls))
 	}
 }
+
+func TestProjectDailyMileageSelectsCandidateAndMarksSource(t *testing.T) {
+	exec := &recordingExec{}
+	err := ProjectDailyMileage(context.Background(), exec, "LA9GG64L7PBAF4001", "2026-07-08", envelope.ProtocolJT808)
+	if err != nil {
+		t.Fatalf("ProjectDailyMileage() error = %v", err)
+	}
+	if len(exec.calls) != 3 {
+		t.Fatalf("exec calls = %d, want 3", len(exec.calls))
+	}
+	updateSources := exec.calls[0].query
+	projectFinal := exec.calls[1].query
+	markSelected := exec.calls[2].query
+	if !strings.Contains(updateSources, "UPDATE vehicle_daily_mileage_source") || !strings.Contains(updateSources, "is_selected = 0") {
+		t.Fatalf("first query should clear selected candidates: %s", updateSources)
+	}
+	for _, want := range []string{
+		"INSERT INTO vehicle_daily_mileage",
+		"FROM vehicle_daily_mileage_source s",
+		"LEFT JOIN vehicle_data_source ds",
+		"ORDER BY COALESCE(ds.trust_priority, 100)",
+		"s.quality_status = 'OK'",
+		"s.daily_mileage_km BETWEEN 0 AND",
+	} {
+		if !strings.Contains(projectFinal, want) {
+			t.Fatalf("project query missing %q: %s", want, projectFinal)
+		}
+	}
+	if !strings.Contains(markSelected, "UPDATE vehicle_daily_mileage_source s") || !strings.Contains(markSelected, "SET s.is_selected = 1") {
+		t.Fatalf("mark query should flag the elected source: %s", markSelected)
+	}
+}