feat(profile): a handle in a studyset opens its person's profile

The summary's first block now reads as a studyset's card: its secondary
title, its title, then by @handle; the blocks' second heading is
Material. A licence holder written as a handle of the instance
(@raisondetredev) reads © raisondetredev, the © standing for the @,
and is a link, apart from a name from elsewhere such as Tae Kim's; it
and the author open their public profile in a sheet: avatar, name,
address, bio and links, as the instance's profiles.byHandle gives them.

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/l10n/app_de.arb

@@ -471,6 +471,9 @@
   "profileSwitchStay": "Anonym bleiben",
   "profileSwitchConfirm": "Wechseln",
   "publicProfileTitle": "Öffentliches Profil",
+  "profileSheetTitle": "Profil",
+  "profileSheetNotFound": "Niemand auf dieser Instanz hat diesen Handle.",
+  "profileSheetUnreachable": "Das Profil konnte nicht geladen werden. Prüfe deine Verbindung.",
   "publicProfileIntro": "Wie andere dich sehen, sobald du veröffentlichst: das Handle, unter dem sie dich finden, dein Name, ein paar Worte und Links. Es speichert sich beim Schreiben, sobald du dein Handle gewählt hast.",
   "publicProfileAnonymousHint": "Melde dich mit GitHub an, um ein öffentliches Profil zu haben und zu veröffentlichen.",
   "publicProfileDisplayName": "Anzeigename",
@@ -1623,7 +1626,7 @@
   "exploreNothingMatches": "Nichts Veröffentlichtes passt dazu.",
   "exploreBy": "von {author}",
   "exploreRelease": "v{version} · {date}",
-  "exploreHolds": "Inhalt",
+  "exploreMaterial": "Material",
   "exploreLatestRelease": "Neueste Veröffentlichung: v{version} · {date}",
   "exploreAddToLibrary": "Zur Bibliothek hinzufügen",
   "exploreAdd": "Hinzufügen",

halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -531,6 +531,9 @@
   "profileSwitchStay": "Stay anonymous",
   "profileSwitchConfirm": "Switch",
   "publicProfileTitle": "Public profile",
+  "profileSheetTitle": "Profile",
+  "profileSheetNotFound": "Nobody on this instance has this handle.",
+  "profileSheetUnreachable": "The profile couldn’t be loaded. Check your connection.",
   "publicProfileIntro": "How others see you once you publish: the handle they find you by, your name, a few words and links. It saves as you write, once you have chosen your handle.",
   "publicProfileAnonymousHint": "Sign in with GitHub to have a public profile and publish.",
   "publicProfileDisplayName": "Display name",
@@ -1904,7 +1907,7 @@
   "@exploreBy": {"placeholders": {"author": {"type": "String"}}},
   "exploreRelease": "v{version} · {date}",
   "@exploreRelease": {"placeholders": {"version": {"type": "int"}, "date": {"type": "String"}}},
-  "exploreHolds": "What it holds",
+  "exploreMaterial": "Material",
   "exploreLatestRelease": "Latest release: v{version} · {date}",
   "@exploreLatestRelease": {"placeholders": {"version": {"type": "int"}, "date": {"type": "String"}}},
   "exploreAddToLibrary": "Add to library",

halkyon_learn_flutter/lib/l10n/app_localizations.dart

@@ -2836,6 +2836,24 @@ abstract class AppLocalizations {
   /// **'Public profile'**
   String get publicProfileTitle;
 
+  /// No description provided for @profileSheetTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Profile'**
+  String get profileSheetTitle;
+
+  /// No description provided for @profileSheetNotFound.
+  ///
+  /// In en, this message translates to:
+  /// **'Nobody on this instance has this handle.'**
+  String get profileSheetNotFound;
+
+  /// No description provided for @profileSheetUnreachable.
+  ///
+  /// In en, this message translates to:
+  /// **'The profile couldn’t be loaded. Check your connection.'**
+  String get profileSheetUnreachable;
+
   /// No description provided for @publicProfileIntro.
   ///
   /// In en, this message translates to:
@@ -9603,11 +9621,11 @@ abstract class AppLocalizations {
   /// **'v{version} · {date}'**
   String exploreRelease(int version, String date);
 
-  /// No description provided for @exploreHolds.
+  /// No description provided for @exploreMaterial.
   ///
   /// In en, this message translates to:
-  /// **'What it holds'**
+  /// **'Material'**
-  String get exploreHolds;
+  String get exploreMaterial;
 
   /// No description provided for @exploreLatestRelease.
   ///

halkyon_learn_flutter/lib/l10n/app_localizations_de.dart

@@ -1739,6 +1739,17 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get publicProfileTitle => 'Öffentliches Profil';
 
+  @override
+  String get profileSheetTitle => 'Profil';
+
+  @override
+  String get profileSheetNotFound =>
+      'Niemand auf dieser Instanz hat diesen Handle.';
+
+  @override
+  String get profileSheetUnreachable =>
+      'Das Profil konnte nicht geladen werden. Prüfe deine Verbindung.';
+
   @override
   String get publicProfileIntro =>
       'Wie andere dich sehen, sobald du veröffentlichst: das Handle, unter dem sie dich finden, dein Name, ein paar Worte und Links. Es speichert sich beim Schreiben, sobald du dein Handle gewählt hast.';
@@ -6045,7 +6056,7 @@ class AppLocalizationsDe extends AppLocalizations {
   }
 
   @override
-  String get exploreHolds => 'Inhalt';
+  String get exploreMaterial => 'Material';
 
   @override
   String exploreLatestRelease(int version, String date) {

halkyon_learn_flutter/lib/l10n/app_localizations_en.dart

@@ -1724,6 +1724,16 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get publicProfileTitle => 'Public profile';
 
+  @override
+  String get profileSheetTitle => 'Profile';
+
+  @override
+  String get profileSheetNotFound => 'Nobody on this instance has this handle.';
+
+  @override
+  String get profileSheetUnreachable =>
+      'The profile couldn’t be loaded. Check your connection.';
+
   @override
   String get publicProfileIntro =>
       'How others see you once you publish: the handle they find you by, your name, a few words and links. It saves as you write, once you have chosen your handle.';
@@ -5992,7 +6002,7 @@ class AppLocalizationsEn extends AppLocalizations {
   }
 
   @override
-  String get exploreHolds => 'What it holds';
+  String get exploreMaterial => 'Material';
 
   @override
   String exploreLatestRelease(int version, String date) {

halkyon_learn_flutter/lib/src/feature/explore/widget/explore_summary_sheet.dart

@@ -4,10 +4,12 @@ import 'package:halkyon_learn_flutter/src/core/editor/rich_content_view.dart';
 import 'package:halkyon_learn_flutter/src/core/l10n/content_languages.dart';
 import 'package:halkyon_learn_flutter/src/core/widget/adaptive_sheet.dart';
 import 'package:halkyon_learn_flutter/src/core/widget/section_card.dart';
+import 'package:halkyon_learn_flutter/src/core/widget/title_with_kicker.dart';
 import 'package:halkyon_learn_flutter/src/feature/explore/bloc/explore_bloc.dart';
 import 'package:halkyon_learn_flutter/src/feature/explore/model/explore_studyset.dart';
 import 'package:halkyon_learn_flutter/src/feature/explore/widget/explore_screen.dart';
 import 'package:halkyon_learn_flutter/src/feature/feedback/widget/feedback_threads.dart';
+import 'package:halkyon_learn_flutter/src/feature/profile/widget/profile_sheet.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/model/studyset_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/widget/license_footer.dart';
 import 'package:lucide_icons_flutter/lucide_icons.dart';
@@ -48,7 +50,9 @@ class const _Summary({required final ExploreStudyset studyset})
     ];
     return BlocBuilder<ExploreBloc, ExploreState>(
       builder: (context, state) => SheetScaffold(
-        title: studyset.title,
+        // Its title is in the first block, under its secondary title, as
+        // the library's cards set it.
+        title: '',
         body: Column(
           crossAxisAlignment: CrossAxisAlignment.stretch,
           children: [
@@ -64,16 +68,23 @@ class const _Summary({required final ExploreStudyset studyset})
                     child: Column(
                       crossAxisAlignment: CrossAxisAlignment.start,
                       children: [
-                        if (studyset.secondaryTitle case final secondary?)
+                        TitleWithKicker(
-                          Text(
+                          title: studyset.title,
-                            secondary,
+                          kicker: studyset.secondaryTitle,
-                            style: theme.textTheme.labelLarge?.copyWith(
+                          titleStyle: theme.textTheme.titleLarge?.copyWith(
+                            fontWeight: FontWeight.w600,
+                          ),
+                        ),
+                        const SizedBox(height: 2),
+                        // The author, whose profile it opens.
+                        InkWell(
+                          onTap: () => showProfileOf(context, studyset.handle),
+                          child: Text(
+                            l10n.exploreBy(authorLine(studyset)),
+                            style: muted?.copyWith(
                               color: theme.colorScheme.primary,
                             ),
                           ),
-                        Text(
-                          l10n.exploreBy(authorLine(studyset)),
-                          style: muted,
                         ),
                         if (studyset.basedOn case final original?)
                           Text(l10n.exploreBasedOn(original), style: muted),
@@ -100,7 +111,7 @@ class const _Summary({required final ExploreStudyset studyset})
               child: Column(
                 crossAxisAlignment: CrossAxisAlignment.start,
                 children: [
-                  Text(l10n.exploreHolds, style: theme.textTheme.titleSmall),
+                  Text(l10n.exploreMaterial, style: theme.textTheme.titleSmall),
                   const SizedBox(height: 8),
                   if (languages.isNotEmpty)
                     Text(

halkyon_learn_flutter/lib/src/feature/profile/data/profile_gateway.dart

@@ -8,6 +8,10 @@ abstract interface class ProfileGateway() {
   /// The person's public profile; null while they have none.
   Future<PublicProfile?> mine();
 
+  /// The public profile of whoever has [handle] on the instance; null
+  /// when nobody has.
+  Future<PublicProfile?> byHandle(String handle);
+
   /// Saves the person's public profile, making it if they have none.
   /// Throws [ProfileRefused] when the instance refuses it.
   Future<PublicProfile> save({

halkyon_learn_flutter/lib/src/feature/profile/data/profile_repository.dart

@@ -15,6 +15,10 @@ class ProfileRepository(
   /// The person's public profile; null while they have none.
   Future<PublicProfile?> mine() => _gateway.mine();
 
+  /// The public profile of whoever has [handle] (without its `@`) on the
+  /// instance; null when nobody has.
+  Future<PublicProfile?> byHandle(String handle) => _gateway.byHandle(handle);
+
   /// Saves the person's public profile, blank links left out. Throws
   /// [ProfileRefused] when the instance refuses it.
   Future<PublicProfile> save({

halkyon_learn_flutter/lib/src/feature/profile/data/serverpod_profile_gateway.dart

@@ -25,6 +25,15 @@ class ServerpodProfileGateway(final protocol.Client _client)
     ),
   );
 
+  @override
+  Future<PublicProfile?> byHandle(String handle) async {
+    try {
+      return _profile(await _client.profiles.byHandle(handle));
+    } on protocol.NotFoundException {
+      return null;
+    }
+  }
+
   @override
   Future<ProfileProblem?> checkHandle(String handle) async =>
       switch (await _client.profile.checkHandle(handle)) {

halkyon_learn_flutter/lib/src/feature/profile/widget/profile_sheet.dart

@@ -0,0 +1,120 @@
+import 'dart:async';
+
+import 'package:halkyon_learn_flutter/l10n/app_localizations.dart';
+import 'package:halkyon_learn_flutter/src/core/dependencies/person_scope.dart';
+import 'package:halkyon_learn_flutter/src/core/widget/adaptive_sheet.dart';
+import 'package:halkyon_learn_flutter/src/core/widget/app_loading_indicator.dart';
+import 'package:halkyon_learn_flutter/src/feature/profile/model/public_profile.dart';
+import 'package:lucide_icons_flutter/lucide_icons.dart';
+import 'package:material_ui/material_ui.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+/// Shows the public profile of whoever has [handle] (without its `@`) on
+/// the instance, as a studyset names its author or licence holder
+/// (decided 2026-10-14): their avatar, name and address, what they say
+/// about themselves and their links; that nobody has it, when nobody has.
+Future<void> showProfileOf(BuildContext context, String handle) {
+  final profiles = PersonScope.of(context).profile;
+  return showAdaptiveSheet<void>(
+    context,
+    builder: (context) => _ProfileSheet(profile: profiles.byHandle(handle)),
+  );
+}
+
+class const _ProfileSheet({required final Future<PublicProfile?> profile})
+    extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    final theme = Theme.of(context);
+    final muted = theme.textTheme.bodyMedium?.copyWith(
+      color: theme.colorScheme.onSurfaceVariant,
+    );
+    return FutureBuilder(
+      future: profile,
+      builder: (context, snapshot) {
+        final found = snapshot.data;
+        return SheetScaffold(
+          title: found == null
+              ? l10n.profileSheetTitle
+              : found.displayName.isEmpty
+              ? '@${found.handle}'
+              : found.displayName,
+          body: switch (snapshot.connectionState) {
+            ConnectionState.done when found == null => Text(
+              snapshot.hasError
+                  ? l10n.profileSheetUnreachable
+                  : l10n.profileSheetNotFound,
+              style: muted,
+            ),
+            ConnectionState.done => _Profile(profile: found!),
+            _ => const Padding(
+              padding: EdgeInsets.symmetric(vertical: 24),
+              child: Center(child: AppLoadingIndicator()),
+            ),
+          },
+        );
+      },
+    );
+  }
+}
+
+class const _Profile({required final PublicProfile profile})
+    extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final muted = theme.textTheme.bodyMedium?.copyWith(
+      color: theme.colorScheme.onSurfaceVariant,
+    );
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.start,
+      children: [
+        Row(
+          children: [
+            CircleAvatar(
+              radius: 28,
+              foregroundImage: switch (profile.avatarUrl) {
+                final url? => NetworkImage(url),
+                null => null,
+              },
+              child: const Icon(LucideIcons.user),
+            ),
+            const SizedBox(width: 16),
+            Expanded(
+              child: Text(
+                '@${profile.address}',
+                style: muted,
+                maxLines: 2,
+                overflow: TextOverflow.ellipsis,
+              ),
+            ),
+          ],
+        ),
+        if (profile.bio.isNotEmpty) ...[
+          const SizedBox(height: 16),
+          Text(profile.bio),
+        ],
+        if (profile.links.isNotEmpty) ...[
+          const SizedBox(height: 12),
+          for (final link in profile.links)
+            ListTile(
+              contentPadding: EdgeInsets.zero,
+              dense: true,
+              leading: const Icon(LucideIcons.link),
+              title: Text(
+                link.replaceFirst(RegExp('^https?://'), ''),
+                maxLines: 1,
+                overflow: TextOverflow.ellipsis,
+              ),
+              onTap: () => unawaited(
+                launchUrl(
+                  Uri.parse(link.contains('://') ? link : 'https://$link'),
+                ),
+              ),
+            ),
+        ],
+      ],
+    );
+  }
+}

halkyon_learn_flutter/lib/src/feature/studyset/widget/license_footer.dart

@@ -1,3 +1,4 @@
+import 'package:halkyon_learn_flutter/src/feature/profile/widget/profile_sheet.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/model/license_link.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/model/studyset_content.dart';
 import 'package:material_ui/material_ui.dart';
@@ -36,11 +37,16 @@ class const LicenseFooter({
       color: theme.colorScheme.onSurfaceVariant,
     );
     // The year sits between the symbol and the holder, as copyright notices
-    // put it, and either can stand alone.
+    // put it, and either can stand alone. A holder written as a handle
+    // (`@raisondetredev`) is a person of the instance: named without the
+    // `@`, which the © already stands for, and a link to their profile,
+    // so they read apart from a name from elsewhere (Tae Kim).
+    final handle = _handle.firstMatch(holder)?.group(1);
     final credit = [
       if (year != null) '$year',
-      if (holder.isNotEmpty) holder,
+      if (holder.isNotEmpty && handle == null) holder,
     ].join(' ');
+    final link = muted?.copyWith(color: theme.colorScheme.primary);
     final url = license.isEmpty ? null : licenseUrl(license);
     // Two lines at most.
     return Padding(
@@ -50,8 +56,17 @@ class const LicenseFooter({
       child: Text.rich(
         TextSpan(
           children: [
-            if (credit.isNotEmpty) TextSpan(text: '© $credit'),
+            if (credit.isNotEmpty || handle != null)
-            if (credit.isNotEmpty && license.isNotEmpty)
+              TextSpan(text: '© $credit${credit.isEmpty ? '' : ' '}'),
+            if (handle != null)
+              WidgetSpan(
+                alignment: PlaceholderAlignment.middle,
+                child: InkWell(
+                  onTap: () => showProfileOf(context, handle),
+                  child: Text(handle, style: link),
+                ),
+              ),
+            if ((credit.isNotEmpty || handle != null) && license.isNotEmpty)
               const TextSpan(text: '  ·  '),
             if (license.isNotEmpty)
               if (url == null)
@@ -61,10 +76,7 @@ class const LicenseFooter({
                   alignment: PlaceholderAlignment.middle,
                   child: InkWell(
                     onTap: () => launchUrl(url),
-                    child: Text(
+                    child: Text('$license ↗', style: link),
-                      '$license ↗',
-                      style: muted?.copyWith(color: theme.colorScheme.primary),
-                    ),
                   ),
                 ),
           ],
@@ -77,3 +89,7 @@ class const LicenseFooter({
     );
   }
 }
+
+/// A holder written as a handle of the instance, `@` and Mastodon's
+/// letters, digits and underscores; the handle without its `@`.
+final _handle = RegExp(r'^@([A-Za-z0-9_]{1,30})$');

halkyon_learn_flutter/test/feature/explore/explore_screen_test.dart

@@ -9,6 +9,7 @@ import 'package:halkyon_learn_flutter/src/feature/auth/model/auth_status.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_payload.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/explore/model/explore_studyset.dart';
+import 'package:halkyon_learn_flutter/src/feature/profile/model/public_profile.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/data/studyset_payload.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/data/studyset_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/studyset/model/studyset_content.dart';
@@ -17,6 +18,7 @@ import 'package:material_ui/material_ui.dart';
 
 import '../../support/fake_auth_gateway.dart';
 import '../../support/fake_explore_gateway.dart';
+import '../../support/fake_profile_gateway.dart';
 import '../../support/fake_studyset_gateway.dart';
 import '../../support/pump_app.dart';
 import '../../support/test_dependencies.dart';
@@ -91,6 +93,7 @@ void main() {
     WidgetTester tester,
     FakeExploreGateway explore, {
     bool identified = true,
+    FakeProfileGateway? profiles,
   }) async {
     tester.view.physicalSize = const Size(900, 1400);
     tester.view.devicePixelRatio = 1;
@@ -106,6 +109,7 @@ void main() {
         ),
         studysetGateway: studysets,
         exploreGateway: explore,
+        profileGateway: profiles,
       ),
       location: RoutePaths.explore,
     );
@@ -242,6 +246,51 @@ void main() {
     );
   });
 
+  testWidgets('a licence holder of the instance is named by their handle, '
+      "without the @, opening their profile; one from elsewhere isn't", (
+    tester,
+  ) async {
+    final japanese = published('Japanese');
+    await showExplore(
+      tester,
+      FakeExploreGateway(
+        published: [
+          ExploreStudyset(
+            publicId: japanese.publicId,
+            location: japanese.location,
+            handle: 'alice',
+            version: 3,
+            releasedAt: japanese.releasedAt,
+            title: 'Japanese',
+            description: japanese.description,
+            license: 'CC-BY-SA-4.0',
+            licenseHolder: '@alice',
+          ),
+        ],
+      ),
+      profiles: FakeProfileGateway(
+        others: {
+          'alice': const PublicProfile(
+            handle: 'alice',
+            address: 'alice@halkyon.eu',
+            displayName: 'Alice',
+            bio: 'Learning Japanese.',
+          ),
+        },
+      ),
+    );
+    await tester.tap(find.text('Japanese'));
+    await tester.pumpAndSettle();
+
+    expect(find.textContaining('@alice', findRichText: true), findsWidgets);
+    expect(find.text('alice'), findsOneWidget);
+    await tester.tap(find.text('alice'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Learning Japanese.'), findsOneWidget);
+    expect(find.text('@alice@halkyon.eu'), findsOneWidget);
+  });
+
   testWidgets('a summary shows all of it, and adds it to the library as '
       'a copy, opened from there', (tester) async {
     await showExplore(

halkyon_learn_flutter/test/support/fake_profile_gateway.dart

@@ -12,7 +12,18 @@ class FakeProfileGateway({
 
   /// Handles others have.
   final Set<String> taken = const {},
+
+  /// Others' profiles, by their handles.
+  final Map<String, PublicProfile> others = const {},
 }) implements ProfileGateway {
+  @override
+  Future<PublicProfile?> byHandle(String handle) async {
+    if (fail case final error?) {
+      throw error;
+    }
+    return others[handle.toLowerCase()];
+  }
+
   /// When set, every request fails with it.
   Exception? fail;