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+# Popular Requests Form Pre-fill Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Make popular request clicks pre-fill the search form on the start page via query params, matching Angular behavior.
+
+**Architecture:** Each start page reads query params via `useSearchParams()` from `@modern-js/runtime/router`. The click handler builds a URL with query params and navigates to the same page. The form initializes state from those params.
+
+**Tech Stack:** React, Modern.js router (`useSearchParams`, `useNavigate`), existing `PopularRequest` types.
+
+---
+
+## File Structure
+
+### Modified files
+- `src/features/online-board/components/OnlineBoardStartPage.tsx` — Add click handler + query param reading + pass initial props to filter
+- `src/features/schedule/components/ScheduleStartPage.tsx` — Add click handler + query param reading + initialize form state from params
+
+### No changes needed
+- `src/features/online-board/components/OnlineBoardFilter.tsx` — Already accepts `initialDeparture`, `initialArrival`, `initialDate`, `initialTab`, `initialFlightNumber` props
+- `src/features/popular-requests/` — No changes to any popular requests components
+
+---
+
+### Task 1: OnlineBoardStartPage — Pre-fill on Popular Request Click
+
+**Files:**
+- Modify: `src/features/online-board/components/OnlineBoardStartPage.tsx`
+
+- [ ] **Step 1: Write the failing test**
+
+Create `src/features/online-board/components/OnlineBoardStartPage.test.tsx`:
+
+```tsx
+import { describe, it, expect, vi } from "vitest";
+import { buildPopularRequestQueryParams } from "./OnlineBoardStartPage.js";
+
+describe("buildPopularRequestQueryParams", () => {
+  it("returns tab=flight with carrier and flight for FlightNumber mode", () => {
+    const params = buildPopularRequestQueryParams({
+      mode: "FlightNumber",
+      carrier: "SU",
+      flightNumber: "0654",
+      type: "Onlineboard",
+    });
+    expect(params.get("tab")).toBe("flight");
+    expect(params.get("carrier")).toBe("SU");
+    expect(params.get("flight")).toBe("0654");
+  });
+
+  it("returns tab=route with departure for Departure mode", () => {
+    const params = buildPopularRequestQueryParams({
+      mode: "Departure",
+      departure: "LED",
+      type: "Onlineboard",
+    });
+    expect(params.get("tab")).toBe("route");
+    expect(params.get("departure")).toBe("LED");
+    expect(params.has("arrival")).toBe(false);
+  });
+
+  it("returns tab=route with arrival for Arrival mode", () => {
+    const params = buildPopularRequestQueryParams({
+      mode: "Arrival",
+      arrival: "VKO",
+      type: "Onlineboard",
+    });
+    expect(params.get("tab")).toBe("route");
+    expect(params.get("arrival")).toBe("VKO");
+    expect(params.has("departure")).toBe(false);
+  });
+
+  it("returns tab=route with both cities for Route mode", () => {
+    const params = buildPopularRequestQueryParams({
+      mode: "Route",
+      departure: "LED",
+      arrival: "KRR",
+      type: "Onlineboard",
+    });
+    expect(params.get("tab")).toBe("route");
+    expect(params.get("departure")).toBe("LED");
+    expect(params.get("arrival")).toBe("KRR");
+  });
+});
+```
+
+- [ ] **Step 2: Run test to verify it fails**
+
+Run: `pnpm vitest run src/features/online-board/components/OnlineBoardStartPage.test.tsx`
+
+Expected: FAIL — `buildPopularRequestQueryParams` is not exported.
+
+- [ ] **Step 3: Implement the query param builder and wire up the component**
+
+Edit `src/features/online-board/components/OnlineBoardStartPage.tsx`. Replace the entire file with:
+
+```tsx
+/**
+ * Online Board start page matching the Angular `online-board-start-page`
+ * component DOM structure and CSS class names.
+ *
+ * Reads query params (set by popular request clicks) and passes them
+ * as initial props to OnlineBoardFilter for form pre-fill.
+ *
+ * @module
+ */
+
+import { type FC, useCallback } from "react";
+import { useNavigate, useParams, useSearchParams } from "@modern-js/runtime/router";
+import { useTranslation } from "@/i18n/provider.js";
+import { PageLayout } from "@/ui/layout/PageLayout.js";
+import { PageTabs } from "@/ui/layout/PageTabs.js";
+import { SearchHistory } from "@/ui/layout/SearchHistory.js";
+import { OnlineBoardFilter } from "./OnlineBoardFilter.js";
+import { PopularRequestsPanel } from "@/features/popular-requests/components/PopularRequestsPanel.js";
+import type { PopularRequest } from "@/features/popular-requests/types.js";
+import "./OnlineBoardStartPage.scss";
+
+/** Build query params from a popular request for form pre-fill. */
+export function buildPopularRequestQueryParams(request: PopularRequest): URLSearchParams {
+  const params = new URLSearchParams();
+
+  switch (request.mode) {
+    case "FlightNumber":
+      params.set("tab", "flight");
+      params.set("carrier", request.carrier);
+      params.set("flight", request.flightNumber);
+      break;
+    case "Departure":
+      params.set("tab", "route");
+      params.set("departure", request.departure);
+      break;
+    case "Arrival":
+      params.set("tab", "route");
+      params.set("arrival", request.arrival);
+      break;
+    case "Route":
+    case "RouteWithBack":
+      params.set("tab", "route");
+      params.set("departure", request.departure);
+      params.set("arrival", request.arrival);
+      break;
+  }
+
+  return params;
+}
+
+export const OnlineBoardStartPage: FC = () => {
+  const { t } = useTranslation();
+  const navigate = useNavigate();
+  const routeParams = useParams<{ lang: string }>();
+  const lang = routeParams.lang ?? "ru";
+  const [searchParams] = useSearchParams();
+
+  const handlePopularRequestClick = useCallback((request: PopularRequest) => {
+    // Schedule-type requests navigate to the schedule page
+    if (request.type === "Schedule") {
+      const params = new URLSearchParams();
+      if (request.mode === "Route" || request.mode === "RouteWithBack") {
+        params.set("departure", request.departure);
+        params.set("arrival", request.arrival);
+        if (request.mode === "RouteWithBack") {
+          params.set("return", "true");
+        }
+      }
+      void navigate(`/${lang}/schedule?${params.toString()}`);
+      return;
+    }
+
+    const qp = buildPopularRequestQueryParams(request);
+    void navigate(`/${lang}/onlineboard?${qp.toString()}`);
+  }, [navigate, lang]);
+
+  // Read query params for filter pre-fill
+  const initialTab = searchParams.get("tab") === "flight" ? "flight" as const : searchParams.has("tab") ? "route" as const : undefined;
+  const initialFlightNumber = searchParams.get("carrier") && searchParams.get("flight")
+    ? `${searchParams.get("carrier")}${searchParams.get("flight")}`
+    : undefined;
+  const initialDeparture = searchParams.get("departure") ?? undefined;
+  const initialArrival = searchParams.get("arrival") ?? undefined;
+
+  return (
+    <div className="online-board-start-page" data-testid="online-board-start">
+      <PageLayout
+        headerLeft={
+          <PageTabs viewType="onlineboard" />
+        }
+        title={
+          <h1 className="text--white page-title">
+            {t("BOARD.TITLE")}
+          </h1>
+        }
+        breadcrumbs={[]}
+        contentLeft={
+          <>
+            <OnlineBoardFilter
+              initialTab={initialTab}
+              initialFlightNumber={initialFlightNumber}
+              initialDeparture={initialDeparture}
+              initialArrival={initialArrival}
+            />
+            <SearchHistory />
+          </>
+        }
+      >
+        <section className="frame">
+          <h2>{t("BOARD.BOARD-START")}</h2>
+
+          <div className="titles-container">
+            <div className="title title1">
+              <a>{t("BOARD.BOARD-START-TITLE1")}</a>
+              <div>
+                {t("BOARD.BOARD-START-TITLE1-DESCRIPTION")}
+              </div>
+            </div>
+
+            <div className="title title2">
+              <a>{t("BOARD.BOARD-START-TITLE2")}</a>
+              <div>
+                {t("BOARD.BOARD-START-TITLE2-DESCRIPTION")}
+              </div>
+            </div>
+
+            <div className="title title3">
+              <a>{t("BOARD.BOARD-START-TITLE3")}</a>
+              <div>
+                {t("BOARD.BOARD-START-TITLE3-DESCRIPTION")}
+              </div>
+            </div>
+
+            <div className="title title4">
+              <a>{t("BOARD.BOARD-START-TITLE4")}</a>
+              <div>
+                {t("BOARD.BOARD-START-TITLE4-DESCRIPTION")}
+              </div>
+            </div>
+          </div>
+
+          <PopularRequestsPanel onRequestClick={handlePopularRequestClick} />
+        </section>
+      </PageLayout>
+    </div>
+  );
+};
+```
+
+- [ ] **Step 4: Run test to verify it passes**
+
+Run: `pnpm vitest run src/features/online-board/components/OnlineBoardStartPage.test.tsx`
+
+Expected: PASS — all 4 tests pass.
+
+- [ ] **Step 5: Run existing tests to check for regressions**
+
+Run: `pnpm test`
+
+Expected: All existing tests pass. No regressions.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/features/online-board/components/OnlineBoardStartPage.tsx src/features/online-board/components/OnlineBoardStartPage.test.tsx
+git commit -m "Wire popular request clicks to pre-fill OnlineBoard filter via query params"
+```
+
+---
+
+### Task 2: ScheduleStartPage — Pre-fill on Popular Request Click
+
+**Files:**
+- Modify: `src/features/schedule/components/ScheduleStartPage.tsx`
+
+- [ ] **Step 1: Write the failing test**
+
+Create `src/features/schedule/components/ScheduleStartPage.test.tsx`:
+
+```tsx
+import { describe, it, expect } from "vitest";
+import { buildSchedulePopularRequestQueryParams } from "./ScheduleStartPage.js";
+
+describe("buildSchedulePopularRequestQueryParams", () => {
+  it("returns departure and arrival for Route mode", () => {
+    const params = buildSchedulePopularRequestQueryParams({
+      mode: "Route",
+      departure: "LED",
+      arrival: "KRR",
+      type: "Schedule",
+    });
+    expect(params.get("departure")).toBe("LED");
+    expect(params.get("arrival")).toBe("KRR");
+    expect(params.has("return")).toBe(false);
+  });
+
+  it("returns departure, arrival, and return=true for RouteWithBack mode", () => {
+    const params = buildSchedulePopularRequestQueryParams({
+      mode: "RouteWithBack",
+      departure: "VKO",
+      arrival: "KUF",
+      type: "Schedule",
+    });
+    expect(params.get("departure")).toBe("VKO");
+    expect(params.get("arrival")).toBe("KUF");
+    expect(params.get("return")).toBe("true");
+  });
+
+  it("returns empty params for non-route modes", () => {
+    const params = buildSchedulePopularRequestQueryParams({
+      mode: "Arrival",
+      arrival: "VKO",
+      type: "Onlineboard",
+    });
+    expect(params.toString()).toBe("");
+  });
+});
+```
+
+- [ ] **Step 2: Run test to verify it fails**
+
+Run: `pnpm vitest run src/features/schedule/components/ScheduleStartPage.test.tsx`
+
+Expected: FAIL — `buildSchedulePopularRequestQueryParams` is not exported.
+
+- [ ] **Step 3: Implement the query param builder and wire up the component**
+
+Edit `src/features/schedule/components/ScheduleStartPage.tsx`. Make these changes:
+
+**Add imports** — add `useSearchParams` to the router import:
+
+```tsx
+import { useNavigate, useParams, useSearchParams } from "@modern-js/runtime/router";
+```
+
+**Add the exported builder function** — after the `addDays` helper, before the component:
+
+```tsx
+/** Build query params from a popular request for schedule form pre-fill. */
+export function buildSchedulePopularRequestQueryParams(request: PopularRequest): URLSearchParams {
+  const params = new URLSearchParams();
+  if (request.mode === "Route" || request.mode === "RouteWithBack") {
+    params.set("departure", request.departure);
+    params.set("arrival", request.arrival);
+    if (request.mode === "RouteWithBack") {
+      params.set("return", "true");
+    }
+  }
+  return params;
+}
+```
+
+**Read search params in the component** — after the `lang` line, add:
+
+```tsx
+const [searchParams] = useSearchParams();
+```
+
+**Initialize form state from query params** — change the `useState` calls:
+
+```tsx
+const [departureAirport, setDepartureAirport] = useState<CitySuggestion | string>(searchParams.get("departure") ?? "");
+const [arrivalAirport, setArrivalAirport] = useState<CitySuggestion | string>(searchParams.get("arrival") ?? "");
+const [dateFrom, setDateFrom] = useState<Date | null>(today);
+const [dateTo, setDateTo] = useState<Date | null>(addDays(today, 7));
+const [timeRange, setTimeRange] = useState<[number, number]>([0, 1440]);
+const [directOnly, setDirectOnly] = useState(false);
+const [isRoundTrip, setIsRoundTrip] = useState(searchParams.get("return") === "true");
+const [returnDateFrom, setReturnDateFrom] = useState<Date | null>(addDays(today, 7));
+const [returnDateTo, setReturnDateTo] = useState<Date | null>(addDays(today, 14));
+const [returnTimeRange, setReturnTimeRange] = useState<[number, number]>([0, 1440]);
+```
+
+**Implement the click handler** — replace the empty callback:
+
+```tsx
+const handlePopularRequestClick = useCallback((request: PopularRequest) => {
+  // Onlineboard-type requests navigate to the onlineboard page
+  if (request.type === "Onlineboard") {
+    const params = new URLSearchParams();
+    switch (request.mode) {
+      case "FlightNumber":
+        params.set("tab", "flight");
+        params.set("carrier", request.carrier);
+        params.set("flight", request.flightNumber);
+        break;
+      case "Departure":
+        params.set("tab", "route");
+        params.set("departure", request.departure);
+        break;
+      case "Arrival":
+        params.set("tab", "route");
+        params.set("arrival", request.arrival);
+        break;
+      case "Route":
+        params.set("tab", "route");
+        params.set("departure", request.departure);
+        params.set("arrival", request.arrival);
+        break;
+    }
+    void navigate(`/${lang}/onlineboard?${params.toString()}`);
+    return;
+  }
+
+  const qp = buildSchedulePopularRequestQueryParams(request);
+  void navigate(`/${lang}/schedule?${qp.toString()}`);
+}, [navigate, lang]);
+```
+
+- [ ] **Step 4: Run test to verify it passes**
+
+Run: `pnpm vitest run src/features/schedule/components/ScheduleStartPage.test.tsx`
+
+Expected: PASS — all 3 tests pass.
+
+- [ ] **Step 5: Run all tests**
+
+Run: `pnpm test`
+
+Expected: All tests pass, no regressions.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/features/schedule/components/ScheduleStartPage.tsx src/features/schedule/components/ScheduleStartPage.test.tsx
+git commit -m "Wire popular request clicks to pre-fill Schedule form via query params"
+```
+
+---
+
+### Task 3: Manual Verification
+
+- [ ] **Step 1: Start the React dev server**
+
+Run: `pnpm dev`
+
+- [ ] **Step 2: Navigate to Online Board start page and test popular requests**
+
+Open `http://localhost:8080/ru/onlineboard` in browser.
+
+Verify:
+- Click each popular request item
+- URL updates with query params (e.g., `?tab=flight&carrier=SU&flight=0654`)
+- Filter form is pre-filled with the correct values
+- Clicking "Search" from the pre-filled form navigates to the correct search results page
+
+- [ ] **Step 3: Navigate to Schedule start page and test popular requests**
+
+Open `http://localhost:8080/ru/schedule` in browser.
+
+Verify:
+- Click a Route-type popular request
+- URL updates with query params (e.g., `?departure=LED&arrival=KRR`)
+- Departure and arrival fields are pre-filled
+- For RouteWithBack: round-trip checkbox is checked
+- Clicking "Search" navigates to schedule search results
+
+- [ ] **Step 4: Run comparison pipeline to verify improvement**
+
+Run: `pnpm compare:behavior`
+
+Expected: Popular requests tests (spec 19) that previously failed should now pass for the React project.