Allow non-null assertions in tests; refactor two production hotspots to drop them

- eslint.config.js: disable no-non-null-assertion for *.test.ts/tsx and
  tests/** (fixture-driven tests routinely use arr[0]! after a length
  check — signal there is low).
- closestFlight.ts: replace flights.legs[0]! / flights[flights.length-1]!
  with explicit null checks.
- FlightDetailsAccordion.tsx: refactor transition + meal/service
  branches to use local consts narrowed by a preceding truthy check,
  dropping the `leg.transition!.registration!` patterns.

Warning count: 190 → 65. Remaining warnings are pre-existing production-code
non-null assertions spread across the codebase.

eslint.config.js

@@ -177,4 +177,16 @@ export default [
       ],
     },
   },
+  // Test files get a looser ruleset: non-null assertions are idiomatic
+  // when fixtures guarantee presence (`arr[0]!` after an explicit length
+  // check). Production code keeps the warning; tests don't.
+  {
+    files: [
+      "src/**/*.test.{ts,tsx}",
+      "tests/**/*.{ts,tsx}",
+    ],
+    rules: {
+      "@typescript-eslint/no-non-null-assertion": "off",
+    },
+  },
 ];

src/features/online-board/closestFlight.ts

@@ -11,13 +11,17 @@
 import type { ISimpleFlight, IFlightLeg } from "./types.js";
 
 function firstLeg(flight: ISimpleFlight): IFlightLeg {
-  return flight.routeType === "Direct" ? flight.leg : flight.legs[0]!;
+  if (flight.routeType === "Direct") return flight.leg;
+  const first = flight.legs[0];
+  if (!first) throw new Error("MultiLeg flight has no legs");
+  return first;
 }
 
 function lastLeg(flight: ISimpleFlight): IFlightLeg {
-  return flight.routeType === "Direct"
-    ? flight.leg
-    : flight.legs[flight.legs.length - 1]!;
+  if (flight.routeType === "Direct") return flight.leg;
+  const last = flight.legs[flight.legs.length - 1];
+  if (!last) throw new Error("MultiLeg flight has no legs");
+  return last;
 }
 
 function pickTime(flight: ISimpleFlight, isArrival: boolean): string | null {
@@ -78,9 +82,14 @@ export function findClosestFlightId(
 
   if (!isTodayYyyymmdd(opts.searchDate, now)) {
     // For future days, show the first flight; for past days, the last.
-    const firstMs = parseTimeMs(pickTime(flights[0]!, opts.isArrival));
-    if (firstMs !== null && nowMs < firstMs) return flights[0]!.id;
-    return flights[flights.length - 1]!.id;
+    // We've already short-circuited on `!flights.length` above so both
+    // ends are defined.
+    const first = flights[0];
+    const last = flights[flights.length - 1];
+    if (!first || !last) return null;
+    const firstMs = parseTimeMs(pickTime(first, opts.isArrival));
+    if (firstMs !== null && nowMs < firstMs) return first.id;
+    return last.id;
   }
 
   let best: string | null = flights[0]?.id ?? null;

src/features/online-board/components/details-panels/FlightDetailsAccordion.tsx

@@ -140,38 +140,38 @@ export const FlightDetailsAccordion: FC<FlightDetailsAccordionProps> = ({ leg, v
 
   const rows: RowDef[] = [];
 
-  if (shouldShowTransition(leg.transition?.registration, leg.status, viewType)) {
-    const item = leg.transition!.registration!;
+  const registration = leg.transition?.registration;
+  if (registration && shouldShowTransition(registration, leg.status, viewType)) {
     rows.push({
       id: "registration",
       icon: ICON_REGISTRATION,
       title: t("DETAILS.REGISTRATION"),
-      statusStatus: item.status,
-      body: <TransitionTimes item={item} testId="registration-times" />,
+      statusStatus: registration.status,
+      body: <TransitionTimes item={registration} testId="registration-times" />,
       legacyTestId: "registration-panel",
       isTransition: true,
     });
   }
-  if (shouldShowTransition(leg.transition?.boarding, leg.status, viewType)) {
-    const item = leg.transition!.boarding!;
+  const boarding = leg.transition?.boarding;
+  if (boarding && shouldShowTransition(boarding, leg.status, viewType)) {
     rows.push({
       id: "boarding",
       icon: ICON_BOARDING,
       title: t("DETAILS.BOARDING"),
-      statusStatus: item.status,
-      body: <TransitionTimes item={item} testId="boarding-times" />,
+      statusStatus: boarding.status,
+      body: <TransitionTimes item={boarding} testId="boarding-times" />,
       legacyTestId: "boarding-panel",
       isTransition: true,
     });
   }
-  if (shouldShowTransition(leg.transition?.deboarding, leg.status, viewType)) {
-    const item = leg.transition!.deboarding!;
+  const deboarding = leg.transition?.deboarding;
+  if (deboarding && shouldShowTransition(deboarding, leg.status, viewType)) {
     rows.push({
       id: "deboarding",
       icon: ICON_DEBOARDING,
       title: t("DETAILS.DEBOARDING"),
-      statusStatus: item.status,
-      body: <TransitionTimes item={item} testId="deboarding-times" />,
+      statusStatus: deboarding.status,
+      body: <TransitionTimes item={deboarding} testId="deboarding-times" />,
       legacyTestId: "deboarding-panel",
       isTransition: true,
     });
@@ -187,20 +187,22 @@ export const FlightDetailsAccordion: FC<FlightDetailsAccordionProps> = ({ leg, v
       body: <AircraftPanel equipment={leg.equipment} />,
     });
   }
-  if ((leg.equipment.meal?.length ?? 0) > 0) {
+  const meals = leg.equipment.meal;
+  if (meals && meals.length > 0) {
     rows.push({
       id: "meal",
       icon: ICON_MEAL,
       title: t("SHARED.FOOD"),
-      body: <MealPanel meals={leg.equipment.meal!} />,
+      body: <MealPanel meals={meals} />,
     });
   }
-  if ((leg.equipment.aircraft?.actual?.onBoardServices?.length ?? 0) > 0) {
+  const onBoardServices = leg.equipment.aircraft?.actual?.onBoardServices;
+  if (onBoardServices && onBoardServices.length > 0) {
     rows.push({
       id: "services",
       icon: ICON_SERVICES,
       title: t("DETAILS.ON_BOARD_SERVICES"),
-      body: <ServicesPanel services={leg.equipment.aircraft!.actual!.onBoardServices!} />,
+      body: <ServicesPanel services={onBoardServices} />,
     });
   }