feat(site-finder): horizon selector (6/12/18) on analysis screen (#996)

Segmented control «Горизонт прогноза» driving the analyze query (?horizon=)
and Section 6's target highlight. Default 12.

- HorizonSelector: radiogroup + a11y radios, tokens-only, tabular-nums,
  disabled while a re-analyze is in flight
- useParcelAnalyzeQuery(cad, horizon=12): horizon in queryKey + ?horizon=;
  keepPreviousData so switching horizon doesn't blank the page to loading
- AnalysisPageContent: horizon state + forecast-poll invalidation on change
- Section6Forecast/ForecastHorizonsBlock: selectedHorizon → target row («Целевой»)

Part of EPIC #958.

frontend/src/app/site-finder/analysis/[cad]/AnalysisPageContent.tsx

@@ -1,7 +1,10 @@
 "use client";
 
+import { useState } from "react";
 import Link from "next/link";
+import { useQueryClient } from "@tanstack/react-query";
 
+import { HorizonSelector } from "@/components/site-finder/HorizonSelector";
 import { Section1ParcelInfo } from "@/components/site-finder/analysis/Section1ParcelInfo";
 import { Section2NetworksUtilities } from "@/components/site-finder/analysis/Section2NetworksUtilities";
 import { Section3SettingsAndCompetitors } from "@/components/site-finder/analysis/Section3SettingsAndCompetitors";
@@ -20,7 +23,23 @@ interface Props {
 // ── Page Content (client — needs TanStack Query) ───────────────────────────────
 
 export function AnalysisPageContent({ cad }: Props) {
-  const { data, isLoading, error } = useParcelAnalyzeQuery(cad);
+  const [horizon, setHorizon] = useState<number>(12);
+  const queryClient = useQueryClient();
+  const { data, isLoading, isFetching, error } = useParcelAnalyzeQuery(
+    cad,
+    horizon,
+  );
+
+  // Changing the horizon re-runs /analyze (expensive ~10-30s), which re-enqueues
+  // the async §22 forecast (recompute ~30-180s). Invalidating ["parcel-forecast",
+  // cad] forces Section 6's poll to re-fetch; until the new run is ready it may
+  // still show the previous run's emphasis. The selectedHorizon prop passed to
+  // Section6Forecast gives an instant client-side target highlight regardless —
+  // that's intended.
+  function handleHorizonChange(h: number) {
+    setHorizon(h);
+    void queryClient.invalidateQueries({ queryKey: ["parcel-forecast", cad] });
+  }
 
   // ── Loading ────────────────────────────────────────────────────────────────
 
@@ -98,6 +117,22 @@ export function AnalysisPageContent({ cad }: Props) {
       {/* Breadcrumb */}
       <Breadcrumb cad={cad} districtName={districtName} areaStr={areaStr} />
 
+      {/* Controls row — horizon selector drives the analyze + forecast queries */}
+      <div
+        style={{
+          display: "flex",
+          justifyContent: "flex-end",
+          alignItems: "center",
+          marginTop: 16,
+        }}
+      >
+        <HorizonSelector
+          value={horizon}
+          onChange={handleHorizonChange}
+          disabled={isFetching}
+        />
+      </div>
+
       {/* Page layout: sidebar (240px) + main scroll */}
       <div
         style={{
@@ -137,7 +172,7 @@ export function AnalysisPageContent({ cad }: Props) {
           <Section5Atmosphere cad={cad} />
 
           {/* Section 6 — IMPLEMENTED in 958-B3 (§22 forecast) */}
-          <Section6Forecast cad={cad} />
+          <Section6Forecast cad={cad} selectedHorizon={horizon} />
         </div>
       </div>
     </main>

frontend/src/components/site-finder/HorizonSelector.tsx

@@ -0,0 +1,85 @@
+"use client";
+
+/**
+ * HorizonSelector — segmented control «Горизонт прогноза» (958-B1 / #996).
+ *
+ * Controlled segmented control over the three forecast horizons accepted by
+ * POST /api/v1/parcels/{cad}/analyze?horizon= (6 / 12 / 18; default 12).
+ * Drives useParcelAnalyzeQuery on the Site Finder analysis screen.
+ *
+ * A11y: role="radiogroup" wrapper + role="radio"/aria-checked per <button>
+ * segment (real buttons → native keyboard focus; visible focus ring kept).
+ */
+
+const HORIZONS = [6, 12, 18] as const;
+
+interface Props {
+  /** Currently selected horizon (one of 6 / 12 / 18). */
+  value: number;
+  /** Called with the newly selected horizon. */
+  onChange: (horizon: number) => void;
+  /** Disable the control while a re-analyze is in flight (prevents spamming). */
+  disabled?: boolean;
+}
+
+export function HorizonSelector({ value, onChange, disabled = false }: Props) {
+  return (
+    <div style={{ display: "flex", alignItems: "center", gap: 12 }}>
+      <span
+        style={{
+          fontSize: 12,
+          fontWeight: 500,
+          letterSpacing: "0.04em",
+          textTransform: "uppercase",
+          color: "var(--fg-secondary)",
+          whiteSpace: "nowrap",
+        }}
+      >
+        Горизонт прогноза
+      </span>
+      <div
+        role="radiogroup"
+        aria-label="Горизонт прогноза"
+        style={{
+          display: "inline-flex",
+          borderRadius: 8,
+          border: "1px solid var(--border-card)",
+          background: "var(--bg-card)",
+          padding: 2,
+          gap: 2,
+          opacity: disabled ? 0.6 : 1,
+        }}
+      >
+        {HORIZONS.map((h) => {
+          const selected = h === value;
+          return (
+            <button
+              key={h}
+              type="button"
+              role="radio"
+              aria-checked={selected}
+              disabled={disabled}
+              onClick={() => onChange(h)}
+              style={{
+                appearance: "none",
+                cursor: disabled ? "not-allowed" : "pointer",
+                padding: "6px 16px",
+                borderRadius: 6,
+                border: "none",
+                background: selected ? "var(--accent)" : "transparent",
+                color: selected ? "var(--fg-on-dark)" : "var(--fg-secondary)",
+                fontSize: 13,
+                fontWeight: selected ? 600 : 500,
+                fontVariantNumeric: "tabular-nums",
+                whiteSpace: "nowrap",
+                transition: "background 0.12s, color 0.12s",
+              }}
+            >
+              {h} мес
+            </button>
+          );
+        })}
+      </div>
+    </div>
+  );
+}

frontend/src/components/site-finder/analysis/ForecastHorizonsBlock.tsx

@@ -23,6 +23,8 @@ import {
 
 interface Props {
   forecasts: DemandSupplyForecast[];
+  /** Horizon (мес) to emphasise as the current target — highlights its row. */
+  targetHorizon?: number;
 }
 
 const TH_STYLE: React.CSSProperties = {
@@ -48,7 +50,7 @@ const TD_STYLE: React.CSSProperties = {
 
 const NUM_TD: React.CSSProperties = { ...TD_STYLE, textAlign: "right" };
 
-export function ForecastHorizonsBlock({ forecasts }: Props) {
+export function ForecastHorizonsBlock({ forecasts, targetHorizon }: Props) {
   if (forecasts.length === 0) {
     return (
       <p style={{ fontSize: 13, color: "var(--fg-tertiary)", margin: 0 }}>
@@ -89,9 +91,37 @@ export function ForecastHorizonsBlock({ forecasts }: Props) {
             {rows.map((f) => {
               const di = f.deficit_index;
               const balanced = Math.abs(di) < DEFICIT_BALANCE_EPS;
+              const isTarget = f.horizon_months === targetHorizon;
               return (
-                <tr key={f.horizon_months}>
-                  <td style={TD_STYLE}>{f.horizon_months} мес.</td>
+                <tr
+                  key={f.horizon_months}
+                  style={
+                    isTarget ? { background: "var(--accent-soft)" } : undefined
+                  }
+                >
+                  <td
+                    style={
+                      isTarget
+                        ? { ...TD_STYLE, fontWeight: 600, color: "var(--accent)" }
+                        : TD_STYLE
+                    }
+                  >
+                    {f.horizon_months} мес.
+                    {isTarget && (
+                      <span
+                        style={{
+                          marginLeft: 8,
+                          fontSize: 11,
+                          fontWeight: 500,
+                          letterSpacing: "0.04em",
+                          textTransform: "uppercase",
+                          color: "var(--accent)",
+                        }}
+                      >
+                        Целевой
+                      </span>
+                    )}
+                  </td>
                   <td style={TD_STYLE}>
                     <Badge variant={deficitVariant(di)} size="sm">
                       {di > 0 ? "+" : ""}

frontend/src/components/site-finder/analysis/Section6Forecast.tsx

@@ -31,6 +31,13 @@ import { CONFIDENCE_RU, deficitVariant, fmtNum } from "./forecast-helpers";
 
 interface Props {
   cad: string;
+  /**
+   * Horizon chosen in the analysis-screen HorizonSelector (6 / 12 / 18). When
+   * set it takes priority over the report-derived horizon so the user's choice
+   * instantly drives which horizon is treated as the target (client-side), even
+   * before the recomputed forecast finishes (see AnalysisPageContent comment).
+   */
+  selectedHorizon?: number;
 }
 
 const ADVISORY_DISCLAIMER =
@@ -48,7 +55,7 @@ function kpiColorForDeficit(deficitIndex: number): "green" | "red" | "neutral" {
 
 // ── Section6Forecast ─────────────────────────────────────────────────────────
 
-export function Section6Forecast({ cad }: Props) {
+export function Section6Forecast({ cad, selectedHorizon }: Props) {
   const { data, isLoading, error } = useParcelForecastQuery(cad);
 
   const isPending =
@@ -136,18 +143,26 @@ export function Section6Forecast({ cad }: Props) {
     );
   }
 
-  return <ForecastReady report={data.report} />;
+  return <ForecastReady report={data.report} selectedHorizon={selectedHorizon} />;
 }
 
 // ── ForecastReady (report present) ───────────────────────────────────────────
 
-function ForecastReady({ report }: { report: ForecastReport }) {
+function ForecastReady({
+  report,
+  selectedHorizon,
+}: {
+  report: ForecastReport;
+  selectedHorizon?: number;
+}) {
   const exec = report.exec_summary;
   const fm = report.future_market;
 
-  // Target horizon: prefer future_supply.horizon_months, else median of meta
-  // horizons, else 12.
+  // Target horizon: the user's HorizonSelector choice wins (instant client-side
+  // highlight), else future_supply.horizon_months, else median of meta horizons,
+  // else 12.
   const targetHorizon =
+    selectedHorizon ??
     fm.future_supply?.horizon_months ??
     medianHorizon(report.meta.horizons) ??
     12;
@@ -267,7 +282,10 @@ function ForecastReady({ report }: { report: ForecastReport }) {
         {/* 6.1 Прогноз по горизонтам */}
         {hasHorizons && (
           <SubBlock id="section-6-1" title="6.1 Прогноз по горизонтам">
-            <ForecastHorizonsBlock forecasts={fm.forecasts_by_horizon} />
+            <ForecastHorizonsBlock
+              forecasts={fm.forecasts_by_horizon}
+              targetHorizon={targetHorizon}
+            />
           </SubBlock>
         )}
 

frontend/src/lib/site-finder-api.ts

@@ -8,7 +8,7 @@
  *  MOCK_POI_SCORE      — uses poi-score.json fixture (B6)
  */
 
-import { useQuery } from "@tanstack/react-query";
+import { keepPreviousData, useQuery } from "@tanstack/react-query";
 import { apiFetch, apiFetchWithStatus } from "@/lib/api";
 import {
   MOCK_PARCELS_BBOX,
@@ -326,21 +326,26 @@ export interface PoiScoreResponse {
 
 // ── Hook: useParcelAnalyzeQuery (B5) ─────────────────────────────────────────
 
-export function useParcelAnalyzeQuery(cad: string) {
+export function useParcelAnalyzeQuery(cad: string, horizon: number = 12) {
   return useQuery({
-    queryKey: ["parcel-analyze", cad],
+    queryKey: ["parcel-analyze", cad, horizon],
     queryFn: async (): Promise<ParcelAnalyzeResponse> => {
       if (MOCK_ANALYZE) {
-        // Return fixture data regardless of cad — for dev only
+        // Return fixture data regardless of cad/horizon — for dev only
         return fixtureAnalyze as ParcelAnalyzeResponse;
       }
+      // Backend accepts ?horizon= ∈ {6,12,18} (default 12; 422 otherwise, #995).
       return apiFetch<ParcelAnalyzeResponse>(
-        `/api/v1/parcels/${encodeURIComponent(cad)}/analyze`,
+        `/api/v1/parcels/${encodeURIComponent(cad)}/analyze?horizon=${horizon}`,
         { method: "POST" },
       );
     },
     staleTime: 5 * 60_000, // 5 min — analyze is expensive
     retry: 1,
+    // Horizon is in the queryKey, so switching it is a fresh cache entry. Keep
+    // the previous analysis on screen while the new horizon re-fetches instead
+    // of blanking the whole page to the loading state on every selector change.
+    placeholderData: keepPreviousData,
   });
 }