feat(suggest): wire autosuggest into the search box behind a flag

Off means off — no combobox role, no listener, no fetch. A test asserts
the absence of the request, not just the absence of the dropdown,
because a hidden-but-fetching control would still be spending the rate
limit on a feature nobody can see.

Enter with no active option falls through to the form's submit handler
and searches the typed text exactly as before. The existing behaviour is
preserved, not replaced, and that has its own test.

Suppressed once the value parses as a postcode: the box takes a name OR
a postcode, and suggesting schools during postcode entry fights the user.

.omniBoxContainer gains position: relative — the dropdown is absolutely
positioned and without it would have anchored to the page instead.

Four render sites, all wired: page.tsx renders HomeView in the success
path AND the catch fallback, and HomeView renders FilterBar as hero AND
sticky. Missing any one would make the flag silently do nothing
somewhere.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

nextjs-app/components/FilterBar.module.css

@@ -48,6 +48,8 @@
   display: flex;
   align-items: center;
   gap: 0.5rem;
+  /* The suggestion dropdown is absolutely positioned against this box. */
+  position: relative;
 }
 
 /* The hero pill: hairline, soft corner, everything else sits inside it. */

nextjs-app/components/FilterBar.tsx

@@ -3,8 +3,11 @@
 import { useState, useCallback, useTransition, useRef, useEffect } from "react";
 import type { ReactNode } from "react";
 import { useRouter, useSearchParams, usePathname } from "next/navigation";
-import { isValidPostcode } from "@/lib/utils";
+import { isValidPostcode, schoolUrl } from "@/lib/utils";
 import { track } from "@/lib/analytics";
+import { useSchoolSuggest } from "@/hooks/useSchoolSuggest";
+import { SuggestList, suggestOptionId } from "./SuggestList";
+import type { Suggestion } from "@/lib/suggest";
 import type { Filters, ResultFilters } from "@/lib/types";
 import styles from "./FilterBar.module.css";
 
@@ -17,6 +20,8 @@ interface FilterBarProps {
   onNearMe?: () => void;
   geoState?: "idle" | "requesting" | "error";
   geoError?: string | null;
+  /** Server-read feature flag. Off means no listener, no fetch, no markup. */
+  autosuggest?: boolean;
 }
 
 /**
@@ -48,6 +53,7 @@ export function FilterBar({
   onNearMe,
   geoState = "idle",
   geoError,
+  autosuggest = false,
 }: FilterBarProps) {
   const router = useRouter();
   const pathname = usePathname();
@@ -62,6 +68,45 @@ export function FilterBar({
 
   const [omniValue, setOmniValue] = useState(initialOmniValue);
 
+  const suggestId = `school-suggest-${isHero ? "hero" : "bar"}`;
+  // Suppressed once the value parses as a postcode: the box takes a school
+  // name OR a postcode, and suggesting schools during postcode entry fights
+  // the user rather than helping them.
+  const suggestEnabled = autosuggest && !isValidPostcode(omniValue);
+  const { suggestions, open, activeIndex, setActiveIndex, close } =
+    useSchoolSuggest(omniValue, suggestEnabled);
+
+  const pickSuggestion = (s: Suggestion) => {
+    close();
+    track('search_submitted', {
+      query: s.school_name.toLowerCase(),
+      via: 'suggestion',
+      urn: s.urn,
+      has_postcode: false,
+      filters_active: '',
+      filters_count: 0,
+    });
+    router.push(schoolUrl(s.urn, s.school_name));
+  };
+
+  const handleOmniKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
+    if (!open) return;
+    if (e.key === "ArrowDown") {
+      e.preventDefault();
+      setActiveIndex(activeIndex + 1 >= suggestions.length ? 0 : activeIndex + 1);
+    } else if (e.key === "ArrowUp") {
+      e.preventDefault();
+      setActiveIndex(activeIndex <= 0 ? suggestions.length - 1 : activeIndex - 1);
+    } else if (e.key === "Escape") {
+      close();
+    } else if (e.key === "Enter" && activeIndex >= 0) {
+      // Only when an option is active. With none, the event falls through to
+      // the form's submit handler and searches the typed text, as it does now.
+      e.preventDefault();
+      pickSuggestion(suggestions[activeIndex]);
+    }
+  };
+
   const currentLA = searchParams.get("local_authority") || "";
   const currentType = searchParams.get("school_type") || "";
   const currentPhase = searchParams.get("phase") || "";
@@ -227,8 +272,19 @@ export function FilterBar({
             type="search"
             value={omniValue}
             onChange={(e) => setOmniValue(e.target.value)}
+            onKeyDown={handleOmniKeyDown}
+            onBlur={close}
             placeholder="School name or postcode"
             className={styles.omniInput}
+            {...(autosuggest ? {
+              role: "combobox",
+              "aria-expanded": open,
+              "aria-controls": suggestId,
+              "aria-autocomplete": "list" as const,
+              "aria-activedescendant":
+                activeIndex >= 0 ? suggestOptionId(suggestId, activeIndex) : undefined,
+              autoComplete: "off",
+            } : {})}
           />
           <button
             type="submit"
@@ -237,6 +293,15 @@ export function FilterBar({
           >
             {isPending ? <div className={styles.spinner}></div> : isHero ? "Search schools" : "Search"}
           </button>
+          {autosuggest && open && (
+            <SuggestList
+              id={suggestId}
+              suggestions={suggestions}
+              activeIndex={activeIndex}
+              onPick={pickSuggestion}
+              onHover={setActiveIndex}
+            />
+          )}
         </div>
         {isHero && (
           <>

nextjs-app/components/HomeView.tsx

@@ -29,6 +29,8 @@ interface HomeViewProps {
   // show (e.g. an active search).
   howItWorks?: React.ReactNode;
   editorial?: React.ReactNode;
+  /** Server-read feature flag, threaded to both FilterBar instances. */
+  autosuggest?: boolean;
 }
 
 function daysUntil(month: number, day: number): number {
@@ -193,7 +195,7 @@ const VALUE_PROPS: ValueProp[] = [
   },
 ];
 
-export function HomeView({ initialSchools, filters, totalSchools, howItWorks, editorial }: HomeViewProps) {
+export function HomeView({ initialSchools, filters, totalSchools, howItWorks, editorial, autosuggest = false }: HomeViewProps) {
   const searchParams = useSearchParams();
   const router = useRouter();
   const pathname = usePathname();
@@ -462,6 +464,7 @@ export function HomeView({ initialSchools, filters, totalSchools, howItWorks, ed
               onNearMe={handleNearMe}
               geoState={geoState}
               geoError={geoError}
+              autosuggest={autosuggest}
             />
           </div>
 
@@ -500,6 +503,7 @@ export function HomeView({ initialSchools, filters, totalSchools, howItWorks, ed
           onNearMe={handleNearMe}
           geoState={geoState}
           geoError={geoError}
+          autosuggest={autosuggest}
         />
       )}