Service history: 0 km is a reading, not a blank

A car collected new sits at 0 km, and every km calculation in the app
quietly refused to work for it. ComputeDerived only filled NextServiceKm
when Km > 0, so a service record entered at 0 produced no next-due
distance at all — the date side worked, because it guards on IsZero(),
which is genuine absence rather than a number that happens to be low.

The same conflation had been copied outward from there. The reminder's
km signal wanted currentKm > 0 before it would count anything down, the
web badge and the service-life ring tested the odometer for truthiness,
formatKm printed an em dash for zero, and fuel and charging rejected a
0 km entry as "odometer (km) is required" — which is the first charge
of an EV on the driveway on delivery day. The phone app carried its own
copy of each. Editing such a car offered an empty odometer box, since
the forms only prefilled a reading above zero.

Everywhere the odometer is a measurement, absence is now tested as
absence: null in the clients, negative on the server, and the required
fields check that the box was filled rather than that the number cleared
zero. Fuel and charging validate Km < 0 instead, and their inputs drop
min="1". Completing a repeating km reminder rolls from the car's actual
reading in every case; the old fallback to the previous target existed
to keep an untracked car off a due date in the past, but CurrentKm +
RepeatKm is ahead of the car by construction, so it could not have
happened.

Left as it was: dueKm, repeatKm and the service intervals, where zero
really does encode "no trigger" and "use the default", and the liters
and kwh checks, since a zero fill is not a fill.

Maintenance is the exception. Its odometer is the one that is genuinely
optional, so zero there still has to mean "not recorded" and those three
sites keep the truthiness test, commented. Fixing that properly wants a
nullable field rather than an int, which is a schema change and its own
commit — the same shape of problem as the latency em dash in 3c4eba8.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

API Server/internal/api/charging.go

@@ -222,8 +222,8 @@ func validateChargingSession(c models.ChargingSession) string {
 		return "car is required"
 	case c.Date.IsZero():
 		return "date is required"
-	case c.Km <= 0:
+	case c.Km < 0:
-		return "odometer (km) is required"
+		return "odometer (km) cannot be negative"
 	case c.Kwh <= 0:
 		return "kwh must be greater than zero"
 	case c.Cost < 0:

API Server/internal/api/fuel.go

@@ -220,8 +220,8 @@ func validateFuelEntry(f models.FuelEntry) string {
 		return "car is required"
 	case f.Date.IsZero():
 		return "date is required"
-	case f.Km <= 0:
+	case f.Km < 0:
-		return "odometer (km) is required"
+		return "odometer (km) cannot be negative"
 	case f.Liters <= 0:
 		return "liters must be greater than zero"
 	case f.Cost < 0:

API Server/internal/api/records_test.go

@@ -0,0 +1,27 @@
+package api
+
+import (
+	"testing"
+	"time"
+
+	"drivervault/apiserver/internal/models"
+)
+
+// A car collected new can be fuelled or charged at 0 km on the forecourt; only
+// a negative reading is impossible.
+func TestZeroKmPassesRecordValidation(t *testing.T) {
+	now := time.Now()
+
+	if got := validateFuelEntry(models.FuelEntry{Car: "c1", Date: now, Km: 0, Liters: 40}); got != "" {
+		t.Errorf("fuel at 0 km rejected: %s", got)
+	}
+	if got := validateFuelEntry(models.FuelEntry{Car: "c1", Date: now, Km: -1, Liters: 40}); got == "" {
+		t.Error("fuel at -1 km accepted")
+	}
+	if got := validateChargingSession(models.ChargingSession{Car: "c1", Date: now, Km: 0, Kwh: 12}); got != "" {
+		t.Errorf("charge at 0 km rejected: %s", got)
+	}
+	if got := validateChargingSession(models.ChargingSession{Car: "c1", Date: now, Km: -1, Kwh: 12}); got == "" {
+		t.Error("charge at -1 km accepted")
+	}
+}

API Server/internal/api/reminders.go

@@ -317,14 +317,12 @@ func (s *Server) handleCompleteReminder(w http.ResponseWriter, r *http.Request)
 			// Roll from where the car actually is: the work was done now, so the
 			// next one is due RepeatKm from this reading, whether it was done
 			// early or late. Rolling from the old target instead would let an
-			// early completion drift the schedule forward for good. The target is
+			// early completion drift the schedule forward for good.
-			// only a fallback for a car whose odometer is untracked (0), where
+			//
-			// rolling from zero would put the next due date in the past.
+			// A reading of 0 rolls from 0 like any other: a car collected new is
-			base := car.CurrentKm
+			// genuinely there, and CurrentKm + RepeatKm is ahead of the car by
-			if base <= 0 {
+			// construction, so this cannot land a target in the past.
-				base = m.DueKm
+			payload["due_km"] = car.CurrentKm + m.RepeatKm
-			}
-			payload["due_km"] = base + m.RepeatKm
 		}
 		payload["done"] = false
 		payload["done_at"] = ""

API Server/internal/models/models.go

@@ -469,6 +469,11 @@ type Session struct {
 // ComputeDerived fills NextServiceDate / NextServiceKm from the car's intervals,
 // reproducing the spreadsheet formulas. Intervals of 0 fall back to the
 // spreadsheet defaults (365 days, 15000 km).
+//
+// Note the asymmetry in what counts as "no reading": a zero date is genuinely
+// absent, but a zero odometer is a reading. A car collected new sits at 0 km
+// and its first service is still due 15000 km later, so 0 has to produce a
+// next-due figure like any other number would.
 func (r *ServiceRecord) ComputeDerived(c *Car) {
 	days := c.ServiceIntervalDays
 	if days <= 0 {
@@ -482,7 +487,7 @@ func (r *ServiceRecord) ComputeDerived(c *Car) {
 		d := r.Date.AddDate(0, 0, days)
 		r.NextServiceDate = &d
 	}
-	if r.Km > 0 {
+	if r.Km >= 0 {
 		n := r.Km + km
 		r.NextServiceKm = &n
 	}
@@ -841,7 +846,10 @@ func (r *Reminder) ComputeReminderDerived(now time.Time, currentKm int) {
 		}
 	}
 
-	if r.DueKm > 0 && currentKm > 0 {
+	// currentKm == 0 is a real odometer, not a missing one — see ComputeDerived.
+	// Without this a brand-new car's first service reminder shows a due date but
+	// never the distance left to run.
+	if r.DueKm > 0 && currentKm >= 0 {
 		left := r.DueKm - currentKm
 		r.KmLeft = &left
 		switch {

API Server/internal/models/service_test.go

@@ -0,0 +1,61 @@
+package models
+
+import (
+	"testing"
+	"time"
+)
+
+// A car collected new sits at 0 km; its first service is still due a full
+// interval later, and the reminder must show the distance left to run.
+func TestZeroKmStillYieldsNextService(t *testing.T) {
+	car := &Car{ServiceIntervalDays: 365, ServiceIntervalKm: 15000, CurrentKm: 0}
+	pickup := time.Date(2026, 8, 10, 0, 0, 0, 0, time.UTC)
+	rec := ServiceRecord{Date: pickup, Km: 0}
+	rec.ComputeDerived(car)
+
+	if rec.NextServiceDate == nil || !rec.NextServiceDate.Equal(pickup.AddDate(0, 0, 365)) {
+		t.Fatalf("next service date = %v", rec.NextServiceDate)
+	}
+	if rec.NextServiceKm == nil {
+		t.Fatal("next service km is nil for a 0 km car")
+	}
+	if *rec.NextServiceKm != 15000 {
+		t.Fatalf("next service km = %d, want 15000", *rec.NextServiceKm)
+	}
+
+	rem := Reminder{DueKm: *rec.NextServiceKm}
+	rem.ComputeReminderDerived(time.Now(), car.CurrentKm)
+	if rem.KmLeft == nil || *rem.KmLeft != 15000 {
+		t.Fatalf("km left = %v, want 15000", rem.KmLeft)
+	}
+	if rem.Status != "upcoming" {
+		t.Fatalf("status = %q, want upcoming", rem.Status)
+	}
+}
+
+// A repeating km reminder completed on a car that reads 0 rolls from 0, not
+// from the old target — the odometer is where the car is, not a missing value.
+func TestZeroKmReminderStatus(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		currentKm int
+		dueKm     int
+		wantLeft  int
+		wantState string
+	}{
+		{"collected new", 0, 15000, 15000, "upcoming"},
+		{"nearly due", 14500, 15000, 500, "due_soon"},
+		{"overdue", 15500, 15000, -500, "overdue"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			rem := Reminder{DueKm: tc.dueKm}
+			rem.ComputeReminderDerived(time.Now(), tc.currentKm)
+			if rem.KmLeft == nil || *rem.KmLeft != tc.wantLeft {
+				t.Fatalf("km left = %v, want %d", rem.KmLeft, tc.wantLeft)
+			}
+			if rem.Status != tc.wantState {
+				t.Fatalf("status = %q, want %q", rem.Status, tc.wantState)
+			}
+		})
+	}
+}

Phone App/lib/format.dart

@@ -37,7 +37,8 @@ String formatDate(DateTime? d) {
   return DateFormat(pattern, _locale).format(d);
 }
 
-String formatKm(int? km) => (km == null || km == 0) ? "—" : "${_num(km)} km";
+// 0 km is a reading — a car collected new — not a blank. See format.js.
+String formatKm(int? km) => km == null ? "—" : "${_num(km)} km";
 
 // The fuel figures. The server sends null for anything it could not derive (a
 // window with a missed fill, a first-ever tank), which reads as "—" rather than
@@ -109,7 +110,7 @@ Status _dateSignal(DateTime? nextDate) {
 }
 
 Status _kmSignal(int currentKm, int? nextKm) {
-  if (currentKm == 0 || nextKm == null) return Status(StatusKey.unknown, t("status.noKm"));
+  if (nextKm == null) return Status(StatusKey.unknown, t("status.noKm"));
   final remaining = nextKm - currentKm;
   if (remaining < 0) return Status(StatusKey.overdue, t("status.serviceOverdueKm", params: {"km": _num(remaining.abs())}));
   if (remaining <= _kmSoon) return Status(StatusKey.soon, t("status.inKm", params: {"km": _num(remaining)}));

Phone App/lib/screens/car_detail_screen.dart

@@ -234,7 +234,7 @@ class _CarDetailScreenState extends State<CarDetailScreen> {
   }
 
   Future<void> _editOdometer(Car car) async {
-    final controller = TextEditingController(text: car.currentKm > 0 ? "${car.currentKm}" : "");
+    final controller = TextEditingController(text: "${car.currentKm}");
     final saved = await showDialog<bool>(
       context: context,
       builder: (ctx) => AlertDialog(
@@ -986,7 +986,7 @@ class _MaintenanceTile extends StatelessWidget {
               context,
               [
                 formatDate(entry.date),
-                if (entry.km > 0) formatKm(entry.km),
+                if (entry.km > 0) formatKm(entry.km), // optional on maintenance
                 _typeLabels[entry.type] ?? entry.type,
                 _statusLabels[entry.status] ?? entry.status,
               ].join(" · ")),
@@ -1623,7 +1623,7 @@ class _ServiceSheetState extends State<_ServiceSheet> {
     super.initState();
     final r = widget.record;
     _date = r?.date ?? DateTime.now();
-    _km = TextEditingController(text: (r != null && r.km > 0) ? "${r.km}" : "");
+    _km = TextEditingController(text: r == null ? "" : "${r.km}");
     _notes = TextEditingController(text: r?.notes ?? "");
     _oil = r?.changedOil ?? true;
     _engine = r?.changedEngineAirFilter ?? false;
@@ -1638,6 +1638,11 @@ class _ServiceSheetState extends State<_ServiceSheet> {
   }
 
   Future<void> _save() async {
+    final km = int.tryParse(_km.text.trim()) ?? 0;
+    if (_km.text.trim().isEmpty || km < 0) {
+      setState(() => _error = "Odometer is required.");
+      return;
+    }
     setState(() {
       _saving = true;
       _error = null;
@@ -1645,7 +1650,7 @@ class _ServiceSheetState extends State<_ServiceSheet> {
     final payload = {
       "car": widget.carId,
       "date": _date.toUtc().toIso8601String(),
-      "km": int.tryParse(_km.text.trim()) ?? 0,
+      "km": km,
       "changedOil": _oil,
       "changedEngineAirFilter": _engine,
       "changedCabinAirFilter": _cabin,
@@ -1713,7 +1718,7 @@ class _ServiceSheetState extends State<_ServiceSheet> {
                 child: TextField(
                   controller: _km,
                   keyboardType: TextInputType.number,
-                  decoration: const InputDecoration(labelText: "Odometer (km)", border: OutlineInputBorder()),
+                  decoration: const InputDecoration(labelText: "Odometer (km) *", border: OutlineInputBorder()),
                 ),
               ),
             ],

Phone App/lib/screens/car_form_sheet.dart

@@ -46,8 +46,8 @@ class _CarFormSheetState extends State<CarFormSheet> {
       "differentialOilSpec": TextEditingController(text: car?.differentialOilSpec ?? ""),
       "brakeFluidSpec": TextEditingController(text: car?.brakeFluidSpec ?? ""),
       "coolantSpec": TextEditingController(text: car?.coolantSpec ?? ""),
-      "currentKm":
+      // 0 is a reading, so it prints; only a car that does not exist yet is blank.
-          TextEditingController(text: (car != null && car.currentKm > 0) ? "${car.currentKm}" : ""),
+      "currentKm": TextEditingController(text: car == null ? "" : "${car.currentKm}"),
       "serviceIntervalDays": TextEditingController(text: "${car?.serviceIntervalDays ?? 365}"),
       "serviceIntervalKm": TextEditingController(text: "${car?.serviceIntervalKm ?? 15000}"),
       "technicalCheckIntervalDays": TextEditingController(

Phone App/lib/screens/dashboard_screen.dart

@@ -263,7 +263,8 @@ class _CarCard extends StatelessWidget {
     final interval = row.car.serviceIntervalKm;
     final nextKm = row.latest?.nextServiceKm ?? 0;
     final currentKm = row.car.currentKm;
-    if (interval <= 0 || nextKm <= 0 || currentKm <= 0) return const [];
+    // A new car reads 0 and belongs at 0% of its interval, not hidden entirely.
+    if (interval <= 0 || nextKm <= 0 || currentKm < 0) return const [];
     final remaining = nextKm - currentKm;
     final pct = (100 * (1 - remaining / interval)).clamp(0, 100).round();
     final tone = status.fg(DriverVault.isDark(context));

Phone App/lib/screens/record_form_sheets.dart

@@ -354,7 +354,7 @@ class _FuelSheetState extends State<FuelSheet> {
     super.initState();
     final e = widget.entry;
     _date = e?.date ?? DateTime.now();
-    _km = TextEditingController(text: (e != null && e.km > 0) ? "${e.km}" : "");
+    _km = TextEditingController(text: e == null ? "" : "${e.km}");
     _liters = TextEditingController(text: (e != null && e.liters > 0) ? "${e.liters}" : "");
     _cost = TextEditingController(text: (e != null && e.cost > 0) ? "${e.cost}" : "");
     // A full tank is the common case and the one that makes the entry count
@@ -383,7 +383,7 @@ class _FuelSheetState extends State<FuelSheet> {
   Future<void> _save() async {
     final km = _int(_km);
     final liters = _num(_liters);
-    if (km <= 0) {
+    if (_km.text.trim().isEmpty || km < 0) {
       setState(() => _error = "Odometer is required.");
       return;
     }
@@ -559,6 +559,8 @@ class _MaintenanceSheetState extends State<MaintenanceSheet> {
     _type = e?.type ?? "repair";
     _status = e?.status ?? "completed";
     _warrantyUntil = e?.warrantyUntil;
+    // Maintenance is the one record whose odometer is optional, so 0 still
+    // reads as "not recorded" here.
     _km = TextEditingController(text: (e != null && e.km > 0) ? "${e.km}" : "");
     _workshop = TextEditingController(text: e?.workshop ?? "");
     _location = TextEditingController(text: e?.location ?? "");
@@ -946,9 +948,7 @@ class _ReminderSheetState extends State<ReminderSheet> {
 
   @override
   Widget build(BuildContext context) {
-    final atKm = widget.car.currentKm > 0
+    final atKm = " The car is at ${formatKm(widget.car.currentKm)} now.";
-        ? " The car is at ${formatKm(widget.car.currentKm)} now."
-        : "";
     return _SheetScaffold(
       title: _isEdit ? "Edit reminder" : "Add reminder",
       error: _error,

Web App/web/src/components/CarFormModal.vue

@@ -29,7 +29,7 @@ const form = ref({
   serviceIntervalDays: props.car?.serviceIntervalDays || 365,
   serviceIntervalKm: props.car?.serviceIntervalKm || 15000,
   technicalCheckIntervalDays: props.car?.technicalCheckIntervalDays || 365,
-  currentKm: props.car?.currentKm || "",
+  currentKm: props.car?.currentKm ?? "",
 });
 
 async function submit() {
@@ -55,7 +55,7 @@ async function submit() {
       serviceIntervalDays: Number(form.value.serviceIntervalDays) || 365,
       serviceIntervalKm: Number(form.value.serviceIntervalKm) || 15000,
       technicalCheckIntervalDays: Number(form.value.technicalCheckIntervalDays) || 365,
-      currentKm: form.value.currentKm ? Number(form.value.currentKm) : 0,
+      currentKm: form.value.currentKm === "" ? 0 : Number(form.value.currentKm),
     };
     const saved = isEdit
       ? await api.updateCar(props.car.id, payload)

Web App/web/src/components/ChargingFormModal.vue

@@ -92,7 +92,7 @@ function payload() {
         </div>
         <div>
           <label class="dh-label">{{ t("forms.charging.odometer") }}</label>
-          <input v-model="form.km" type="number" min="1" required placeholder="16138" class="dh-input data" />
+          <input v-model="form.km" type="number" min="0" required placeholder="16138" class="dh-input data" />
         </div>
       </div>
 

Web App/web/src/components/FuelFormModal.vue

@@ -86,7 +86,7 @@ function payload() {
         </div>
         <div>
           <label class="dh-label">{{ t("forms.fuel.odometer") }}</label>
-          <input v-model="form.km" type="number" min="1" required placeholder="16138" class="dh-input data" />
+          <input v-model="form.km" type="number" min="0" required placeholder="16138" class="dh-input data" />
         </div>
       </div>
 

Web App/web/src/components/ReminderFormModal.vue

@@ -102,7 +102,7 @@ function payload() {
         </div>
         <p class="mt-1.5 text-xs text-muted">
           {{ t("forms.reminder.triggerHint") }}
-          <span v-if="car?.currentKm"> {{ t("forms.reminder.currentKm", { km: formatKm(car.currentKm) }) }}</span>
+          <span v-if="car?.currentKm != null"> {{ t("forms.reminder.currentKm", { km: formatKm(car.currentKm) }) }}</span>
         </p>
       </fieldset>
 

Web App/web/src/components/ServiceFormModal.vue

@@ -41,7 +41,9 @@ async function submit() {
     const payload = {
       car: props.carId,
       date: new Date(form.value.date).toISOString(),
-      km: form.value.km ? Number(form.value.km) : 0,
+      // Blank-tested, not truthiness-tested: a service logged at 0 km on a car
+      // collected new is a real entry, and the field is required anyway.
+      km: form.value.km === "" ? 0 : Number(form.value.km),
       changedOil: form.value.changedOil,
       changedEngineAirFilter: form.value.changedEngineAirFilter,
       changedCabinAirFilter: form.value.changedCabinAirFilter,
@@ -73,7 +75,7 @@ async function submit() {
         </div>
         <div>
           <label class="dh-label">{{ t("forms.service.odometer") }}</label>
-          <input v-model="form.km" type="number" placeholder="16138" class="dh-input data" />
+          <input v-model="form.km" type="number" min="0" required placeholder="16138" class="dh-input data" />
         </div>
       </div>
       <fieldset class="rounded-control border border-subtle p-3">

Web App/web/src/lib/format.js

@@ -48,8 +48,12 @@ function num(value) {
   return Number(value).toLocaleString(prefs.locale || undefined);
 }
 
+// 0 prints as "0 km", not "—": a car picked up new has an odometer reading, and
+// blanking it hides the very number the first service interval counts from.
+// Nothing stores a placeholder 0 for the intervals — the server defaults those
+// (applyCarDefaults) — so a zero reaching here is a real reading.
 export function formatKm(value) {
-  if (value == null || value === "" || value === 0) return "—";
+  if (value == null || value === "") return "—";
   return num(value) + " km";
 }
 
@@ -88,9 +92,11 @@ function dateSignal(nextServiceDate) {
   return { key: "ok", label: t("status.okDays", { days }) };
 }
 
-// kmSignal classifies the current odometer against the next-due km.
+// kmSignal classifies the current odometer against the next-due km. Both values
+// are tested for absence rather than truthiness: 0 km is where a new car starts,
+// and reading that as "no data" strands the km signal until the first drive.
 function kmSignal(currentKm, nextServiceKm) {
-  if (!currentKm || !nextServiceKm) return { key: "unknown", label: t("status.noKm") };
+  if (currentKm == null || nextServiceKm == null) return { key: "unknown", label: t("status.noKm") };
   const remaining = nextServiceKm - currentKm;
   if (remaining < 0) return { key: "overdue", label: t("status.serviceOverdueKm", { km: num(Math.abs(remaining)) }) };
   if (remaining <= KM_SOON) return { key: "soon", label: t("status.inKm", { km: num(remaining) }) };

Web App/web/src/views/Dashboard.vue

@@ -129,7 +129,8 @@ function serviceLife(car) {
   const interval = Number(car.serviceIntervalKm);
   const nextKm = Number(car.latest?.nextServiceKm);
   const currentKm = Number(car.currentKm);
-  if (!interval || !nextKm || !currentKm) return null;
+  // A new car reads 0 and belongs at 0% of its interval, not hidden entirely.
+  if (!interval || !nextKm || !Number.isFinite(currentKm)) return null;
   const remaining = nextKm - currentKm;
   const pct = Math.max(0, Math.min(100, Math.round((1 - remaining / interval) * 100)));
   return { pct, tone: TONE_COLOR[serviceStatus(car.latest, car).key] || TONE_COLOR.unknown };