팬덤 탈퇴 · 성운 창립자 권한 승계 · 대표 팬덤 자동 지정

app/lib/features/planet/planet_detail_screen.dart

@@ -6,6 +6,7 @@ import '../../core/data/backend.dart' show BackendException;
 import '../../core/data/planet_visual_state.dart';
 
 import '../../core/theme/tokens.dart';
+import '../../core/ui/app_dialog.dart';
 import '../../core/ui/app_icons.dart';
 import '../eclipse/eclipse_data.dart';
 import '../eclipse/widgets/eclipse_banner.dart';
@@ -74,6 +75,30 @@ class _PlanetDetailScreenState extends State<PlanetDetailScreen> {
     }
   }
 
+  /// 「가입중」 알약 → 탈퇴 시트 → 확인 창 — Figma `343:213428`(탈퇴하기 · 취소) ·
+  /// `343:213582`(행성 탈퇴를 할까요?). 대표 팬덤 자동 지정 · 성운 창립자 승계는 서버 몫이다(C-100 · C-101).
+  void _leave() => showActionSheet(context, [
+    ActionSheetItem(context.l10n.planetLeave, () async {
+      final ok = await showConfirmDialog(
+        context,
+        context.l10n.planetLeaveConfirmTitle,
+        body: context.l10n.planetLeaveConfirmBody,
+        confirmLabel: context.l10n.commonConfirm,
+      );
+      if (!ok) return;
+      try {
+        await widget.repository.leave();
+        if (mounted) {
+          setState(() { _detail = widget.repository.load(nebula: widget.nebula); });
+        }
+      } on BackendException catch (e) {
+        if (mounted) {
+          ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(e.message)));
+        }
+      }
+    }),
+  ]);
+
   @override
   Widget build(BuildContext context) => FutureBuilder<PlanetDetail>(
     future: _detail,
@@ -127,7 +152,7 @@ class _PlanetDetailScreenState extends State<PlanetDetailScreen> {
                       ownerName: d.ownerName,
                       ownerPhoto: d.ownerPhoto,
                       joined: d.joined,
-                      onJoin: d.joined ? null : _join,
+                      onJoin: d.joined ? _leave : _join,
                       onOpenHistory: () => Navigator.of(context).push(
                         MaterialPageRoute<void>(
                           builder: (_) => PlanetHistoryScreen(