v0.1.4: fix silent failure on zones that reject ParkingEstimateMulti

Some zones (e.g. short-term "DL" spaces at the downtown lot) return
Response.Status:Error "Unable to process your request" for ParkingEstimateMulti
even though the single-duration ParkingEstimate works. The screen swallowed that
error -> empty duration list, disabled Pay button, no message ("nothing happens").

- Fall back to a single-estimate ladder across the zone's Min/Max time so these
  zones are purchasable (verified live: flat ~$0.10 up to ~33 min).
- Surface estimate errors with a message + Try again, instead of a blank screen.
- Log the estimate fallback/failure to the on-device diagnostics log.

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

app/src/screens/StartSessionScreen.tsx

@@ -34,6 +34,45 @@ function fmtDuration(min?: number): string {
 }
 const money = (v?: string | number) => `$${Number(v ?? 0).toFixed(2)}`;
 
+/**
+ * Some zones (e.g. short-term "DL" spaces) reject ParkingEstimateMulti with
+ * "Unable to process your request" even though the single-duration estimate
+ * works. Build a price ladder from ParkingEstimate (single) across the zone's
+ * Min/Max time so those zones stay purchasable instead of showing a blank screen.
+ */
+async function buildSingleLadder(base: {
+  zoneId: number;
+  spaceId: number;
+  customerId: number;
+  vehicleId: number;
+}): Promise<ParkingDetail[]> {
+  const probe = await ps.getParkingEstimateSingle({ ...base, durationInMinutes: 30, creditCardId: 0 });
+  if ((probe as any)?.Response?.Status === 'Error') {
+    throw new Error((probe as any).Response?.Message || 'Estimate unavailable for this space.');
+  }
+  const min = Math.max(5, Number(probe.MinTime) || 5);
+  const max = Math.max(min, Number(probe.MaxTime) || min);
+  const span = max - min;
+  const step = span > 180 ? 30 : span > 60 ? 15 : span > 20 ? 10 : 5;
+  const durs = new Set<number>();
+  for (let d = min; d < max; d += step) durs.add(d);
+  durs.add(max);
+  const rungs = await Promise.all(
+    [...durs].map(async (d) => {
+      try {
+        const r = await ps.getParkingEstimateSingle({ ...base, durationInMinutes: d, creditCardId: 0 });
+        const p = r.ParkingDetail;
+        if (!p || (r as any)?.Response?.Status === 'Error') return null;
+        // The single endpoint often echoes Minutes:0; trust the requested duration.
+        return { ...p, Minutes: d } as ParkingDetail;
+      } catch {
+        return null;
+      }
+    }),
+  );
+  return rungs.filter((r): r is ParkingDetail => r != null);
+}
+
 /** Parse the API's "MM-DD-YYYY hh:mm AM" end-time string into a Date for reminders. */
 function parseApiTime(s?: string): Date | null {
   if (!s) return null;
@@ -67,6 +106,7 @@ export function StartSessionScreen() {
   const [selIdx, setSelIdx] = useState(0);
   const [loading, setLoading] = useState(true);
   const [paying, setPaying] = useState(false);
+  const [ladderError, setLadderError] = useState<string | null>(null);
 
   // Load the account's vehicles + cards and pick the defaults.
   useEffect(() => {
@@ -88,16 +128,41 @@ export function StartSessionScreen() {
   const loadLadder = useCallback(async () => {
     if (vehicleId == null || space?.SpaceId == null) return;
     setLoading(true);
+    setLadderError(null);
+    const base = {
+      zoneId: zone.ZoneId!,
+      spaceId: space.SpaceId!,
+      customerId: zone.CustomerId!,
+      vehicleId,
+    };
     try {
-      const est = await ps.getParkingEstimateMulti({
-        zoneId: zone.ZoneId!,
-        spaceId: space.SpaceId!,
-        customerId: zone.CustomerId!,
-        vehicleId,
-      });
-      const details = est.ParkingDetail ?? [];
+      let details: ParkingDetail[] = [];
+      let multiErrored = false;
+      try {
+        const est = await ps.getParkingEstimateMulti(base);
+        if ((est as any)?.Response?.Status === 'Error') multiErrored = true;
+        else details = est.ParkingDetail ?? [];
+      } catch {
+        multiErrored = true;
+      }
+      // Multi is unsupported or empty for some zones — fall back to single estimates.
+      if (!details.length) {
+        logLine(
+          `[ESTIMATE] multi ${multiErrored ? 'errored' : 'empty'} for zone=${base.zoneId} ` +
+            `space=${base.spaceId}; falling back to single`,
+        );
+        details = await buildSingleLadder(base);
+      }
+      if (!details.length) {
+        throw new Error('No parking options are available for this space right now.');
+      }
       setLadder(details);
       setSelIdx((i) => Math.min(i, Math.max(0, details.length - 1)));
+    } catch (e: any) {
+      const msg = e?.serverMessage ?? e?.message ?? 'Could not load parking options.';
+      setLadder([]);
+      setLadderError(msg);
+      logLine(`[ESTIMATE] failed zone=${base.zoneId} space=${base.spaceId}: ${msg}`);
     } finally {
       setLoading(false);
     }
@@ -218,6 +283,26 @@ export function StartSessionScreen() {
     );
   }
 
+  if (ladderError && !ladder.length) {
+    return (
+      <View style={[styles.center, { backgroundColor: colors.bg, padding: 24 }]}>
+        <Text style={[styles.zone, { color: colors.text }]}>{zone.ZoneName}</Text>
+        <View style={[styles.freeBanner, { backgroundColor: '#fdecea', marginTop: 16, alignSelf: 'stretch' }]}>
+          <Text style={{ color: '#c0392b', fontWeight: '700', fontSize: 16 }}>
+            Couldn’t load parking options
+          </Text>
+          <Text style={{ color: colors.subtext, marginTop: 6 }}>{ladderError}</Text>
+        </View>
+        <TouchableOpacity
+          style={[styles.payBtn, { backgroundColor: colors.primary, marginTop: 20, alignSelf: 'stretch' }]}
+          onPress={() => void loadLadder()}
+        >
+          <Text style={styles.payText}>Try again</Text>
+        </TouchableOpacity>
+      </View>
+    );
+  }
+
   const Chip = ({
     active,
     label,