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+# Flights Mini-List Sidebar (B.2)
+
+## Goal
+
+Add a left sidebar on the Online Board flight details page showing all flights with the same flight number on different dates, matching Angular's mini-list behavior. Clicking an item navigates to that flight's details; the current flight is highlighted and auto-scrolled into view.
+
+## Scope
+
+Sub-feature **B.2** of the Flight Details parity work. Online Board only — the Schedule details page mini-list (accordion grouped by date) is a separate concern and out of scope here.
+
+## Current State
+
+- React `OnlineBoardDetailsPage` uses a custom standalone layout (no sidebar).
+- `useFlightDetails` fetches `/onlineboard/details` and returns `response.data.routes[0]`, discarding the rest of the array.
+- The Angular equivalent (`online-board-flights-mini-list`) renders a left-column sidebar (285px desktop, hidden below 1050px) with the full `routes` array.
+
+## Approach
+
+Three changes, three focused commits:
+
+1. **Extend `useFlightDetails`** to return both `flight` (for current display) and `allFlights` (for the list). The API already returns the array; we're just exposing it.
+2. **Add `FlightsMiniList` + `FlightsMiniListItem`** components with auto-scroll-into-view and Link-based navigation.
+3. **Refactor `OnlineBoardDetailsPage`** to use `PageLayout`, putting the mini-list in `contentLeft`.
+
+## Architecture
+
+### Hook: `useFlightDetails` (extended)
+
+Before:
+```typescript
+interface UseFlightDetailsResult {
+  flight: ISimpleFlight | null;
+  loading: boolean;
+  error: ApiError | null;
+}
+```
+
+After:
+```typescript
+interface UseFlightDetailsResult {
+  flight: ISimpleFlight | null;
+  allFlights: ISimpleFlight[];
+  loading: boolean;
+  error: ApiError | null;
+}
+```
+
+Implementation: store `response.data.routes` as `allFlights`, set `flight = allFlights[0] ?? null`.
+
+### Component: `FlightsMiniList`
+
+```typescript
+interface FlightsMiniListProps {
+  flights: ISimpleFlight[];
+  currentFlight: ISimpleFlight;
+}
+```
+
+- Returns `null` when `flights.length <= 1` (nothing to navigate between).
+- Maps to `FlightsMiniListItem` per flight.
+- Uses a `Map<string, HTMLAnchorElement>` ref to track item nodes by `flight.id`.
+- `useEffect([currentFlight.id])` calls `scrollIntoView({ block: "center", behavior: "smooth" })` on the selected item.
+
+### Component: `FlightsMiniListItem`
+
+```typescript
+interface FlightsMiniListItemProps {
+  flight: ISimpleFlight;
+  isSelected: boolean;
+}
+```
+
+- Renders a React Router `<Link>` to the flight's details URL.
+- URL built via `buildFlightDetailsUrl(flight, lang)` — add helper to `src/features/online-board/url.ts` if absent.
+- DOM structure:
+  - `.mini-list__flight-number` (e.g., "SU 0022")
+  - `.mini-list__content` 2x2 CSS Grid:
+    - Row 1: `.mini-list__dep-time` | `.mini-list__status-icon` | `.mini-list__arr-time`
+    - Row 2: `.mini-list__dep-station` | — | `.mini-list__arr-station`
+- Times prefer latest (`actualBlockOff?.local ?? scheduledDeparture.local`).
+- Multi-leg: use `legs[0].departure` and `legs[legs.length - 1].arrival`.
+- Direct: use `leg.departure` and `leg.arrival`.
+- Applies `--selected` modifier class when `isSelected`.
+- Status icon: existing `FlightStatus` component.
+
+### URL Helper
+
+If `src/features/online-board/url.ts` doesn't already export `buildFlightDetailsUrl`, add:
+
+```typescript
+export function buildFlightDetailsUrl(flight: ISimpleFlight, lang: string): string {
+  const { carrier, flightNumber, suffix, date } = flight.flightId;
+  const suffixStr = suffix ?? "";
+  // date is already YYYYMMDD in IFlightId
+  return `/${lang}/onlineboard/${carrier}${flightNumber}${suffixStr}-${date}`;
+}
+```
+
+### Integration: `OnlineBoardDetailsPage`
+
+Wrap the current content in `PageLayout`:
+
+```tsx
+return (
+  <>
+    <SeoHead {...seoProps} />
+    <JsonLdRenderer data={jsonLdData} />
+    <PageLayout
+      headerLeft={<PageTabs viewType="onlineboard" />}
+      title={<h1 className="flight-details__title">{flightNumberFormatted}</h1>}
+      breadcrumbs={[
+        { label: t("BREADCRUMBS.ONLINEBOARD"), href: `/${locale}/onlineboard` },
+        { label: flightNumberFormatted },
+      ]}
+      contentLeft={
+        <FlightsMiniList
+          flights={allFlights}
+          currentFlight={displayFlight}
+        />
+      }
+    >
+      <div className="flight-details">
+        {/* existing content: connection status, summary card, legs, accordion, flying time */}
+      </div>
+    </PageLayout>
+  </>
+);
+```
+
+Loading/error/not-found states render inside the `PageLayout` children so the sidebar still shows.
+
+## Styling
+
+`FlightsMiniList.scss`:
+
+```scss
+.mini-list {
+  display: flex;
+  flex-direction: column;
+  max-height: calc(100vh - 170px);
+  overflow-y: auto;
+  background: #fff;
+  border-radius: 8px;
+
+  &__item {
+    padding: 12px;
+    border-bottom: 1px solid #e0e0e0;
+    text-decoration: none;
+    color: inherit;
+    display: block;
+
+    &:last-child { border-bottom: none; }
+    &:hover { background: #f8f9fa; }
+    &--selected {
+      border: 2px solid #2060c0;
+      border-radius: 4px;
+    }
+  }
+
+  &__flight-number {
+    font-size: 12px;
+    color: #666;
+    margin-bottom: 4px;
+  }
+
+  &__content {
+    display: grid;
+    grid-template-columns: 1fr auto 1fr;
+    grid-template-rows: auto auto;
+    gap: 8px 12px;
+  }
+
+  &__dep-time, &__arr-time {
+    font-size: 16px;
+    font-weight: 500;
+    color: #1a3a5c;
+  }
+  &__arr-time { text-align: right; }
+
+  &__status-icon { grid-column: 2; grid-row: 1; }
+  &__dep-station { grid-column: 1; grid-row: 2; }
+  &__arr-station { grid-column: 3; grid-row: 2; text-align: right; }
+}
+```
+
+Responsive hiding (tablet/mobile) is handled by `PageLayout` — no extra CSS needed at the mini-list level.
+
+## Testing
+
+### Hook test (extend `useFlightDetails.test.ts`)
+
+- Returns `allFlights` = `response.data.routes` array.
+- Returns `flight === allFlights[0]`.
+- Returns `allFlights: []` when response is empty or errors.
+
+### `FlightsMiniList.test.tsx`
+
+- Returns null when `flights.length <= 1`.
+- Renders one item per flight.
+- Highlights the item matching `currentFlight.id`.
+- Calls `scrollIntoView` on the selected item's element (mocked).
+- Works with both Direct and MultiLeg flights.
+
+### `FlightsMiniListItem.test.tsx`
+
+- Renders flight number, dep/arr times, station codes.
+- Has `data-testid="mini-list-item-{id}"`.
+- `<Link>` `href` points to the correct details URL.
+- Applies `--selected` modifier when `isSelected=true`.
+- Multi-leg flight: shows first leg's departure and last leg's arrival stations.
+
+### `OnlineBoardDetailsPage.test.tsx` (update existing)
+
+- Still passes the accordion integration tests from B.1.
+- Renders `PageLayout` wrapper (check for page-layout class or testid).
+- Mini-list visible when mock returns multiple flights.
+- Mini-list not visible when mock returns single flight.
+
+## i18n Keys
+
+Reuse existing. Only one new key likely needed: `BREADCRUMBS.ONLINEBOARD` (check existing — the start page likely uses it already). No new keys specific to the mini-list contents (flight number, times, station codes are data, not labels).
+
+## Out of Scope
+
+- Schedule details page mini-list (separate accordion-grouped component).
+- Day tabs (B.3).
+- Status header action buttons (B.4).
+- Transfer / multi-leg timeline (B.5).
+- Back button / flight schedule timeline (B.6).
+- Changes to SignalR integration.