fix(study): a map question names none of Japan's parts before it is answered

The chips above Japan's map (Hokkaidō, Tōhoku, Kantō …) showed while a
prefecture's question was answered: Hokkaidō's and Okinawa's chip was
the answer itself, and the others named the region the prefecture lies
in. A study card now offers them only once checked; tapping the map
still opens the part tapped. The world's continents keep their chips:
shortcuts no question asks for. Writing a question offers them all, as
before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/src/feature/geo_map/widget/region_map.dart

@@ -83,6 +83,13 @@ class const RegionMap({
   /// Whether the mouse's wheel zooms without Ctrl (or ⌘): where nothing
   /// around the map scrolls.
   final bool wheelZooms = false,
+
+  /// Whether a country's own map offers a chip for each of its parts
+  /// (Japan's Kantō, Kansai …), as while writing a question (decided
+  /// 2026-10-14). While answering one they would give it away: a part may
+  /// be the answer itself (Hokkaidō, Okinawa), or name where it lies. The
+  /// world's continents keep theirs, as shortcuts no question asks for.
+  final bool namesCountryParts = true,
   super.key,
 }) extends StatefulWidget {
   @override
@@ -509,6 +516,7 @@ class RegionMapState()
     final above = atlas.above(_level);
     final header = _Header(
       level: _level,
+      chips: widget.namesCountryParts || _level.map == atlas.world,
       above: above,
       opens: [
         if (widget.countryTaps == CountryTaps.pickOrOpen &&
@@ -547,11 +555,12 @@ class RegionMapState()
 }
 
 /// Above the map: Back to the layer [above], if any; on a whole map a chip
-/// per group, which opens it; in a group its name, and a chip for each map
-/// within a country of it that one may [opens] (Japan's prefectures, once
-/// Japan is picked).
+/// per group, which opens it, unless without [chips]; in a group its name,
+/// and a chip for each map within a country of it that one may [opens]
+/// (Japan's prefectures, once Japan is picked).
 class const _Header({
   required final MapLevel level,
+  required final bool chips,
   required final MapLevel? above,
   required final List<GeoMap> opens,
   required final VoidCallback? onBack,
@@ -576,6 +585,7 @@ class const _Header({
           ],
           Expanded(
             child: switch (level.group) {
+              null when !chips => const SizedBox.shrink(),
               null => ListView.separated(
                 scrollDirection: Axis.horizontal,
                 itemCount: level.map.groups.length,

halkyon_learn_flutter/lib/src/feature/study/widget/study_card_body.dart

@@ -1365,6 +1365,9 @@ class _MapBodyState() extends State<MapBody> {
                             countryTaps: atlas.mapOf(right) == atlas.world
                                 ? CountryTaps.pick
                                 : CountryTaps.open,
+                            // Japan's regions named before the answer would
+                            // give it away.
+                            namesCountryParts: widget.checked,
                             selected: widget.checked ? null : _picked,
                             right: widget.checked ? right : null,
                             wrong: widget.checked && _picked != right

halkyon_learn_flutter/test/feature/geo_map/widget/region_map_test.dart

@@ -28,6 +28,7 @@ void main() {
     String? right,
     String? wrong,
     bool readOnly = false,
+    bool namesCountryParts = true,
   }) async {
     tester.view
       ..physicalSize = const Size(400, 640)
@@ -52,6 +53,7 @@ void main() {
                 selected: picked.lastOrNull,
                 right: right,
                 wrong: wrong,
+                namesCountryParts: namesCountryParts,
                 onRegionTapped: readOnly
                     ? null
                     : (code) => setState(() => picked.add(code)),
@@ -102,6 +104,35 @@ void main() {
 
   const tokyo = (139.69, 35.69);
 
+  testWidgets("while answering, Japan's parts have no chips, which would "
+      "name the answer or where it lies; the map opens them at a tap, and the "
+      "world's continents keep theirs", (tester) async {
+    final picked = await show(
+      tester,
+      countryTaps: CountryTaps.open,
+      // The questions studied, all prefectures: on the whole of Japan.
+      around: {'JP-13', 'JP-27'},
+      namesCountryParts: false,
+    );
+
+    expect(back('East Asia'), findsOneWidget);
+    expect(chip('Hokkaidō'), findsNothing);
+    expect(chip('Kantō'), findsNothing);
+    await tapAt(tester, tokyo);
+    expect(find.text('Kantō'), findsOneWidget);
+    await tapAt(tester, tokyo);
+    expect(picked, ['JP-13']);
+
+    await tester.tap(back('Japan'));
+    await tester.pumpAndSettle();
+    expect(chip('Okinawa'), findsNothing);
+    await tester.tap(back('East Asia'));
+    await tester.pumpAndSettle();
+    await tester.tap(back('World'));
+    await tester.pumpAndSettle();
+    expect(chip('Europe'), findsOneWidget);
+  });
+
   testWidgets('Japan is picked in East Asia, and once it is, a chip opens '
       'its prefectures in layers; Back goes up one', (tester) async {
     final picked = await show(tester);