feat(learn): the assistant's field spans the screen, its buttons boxed and still as who answers changes

Following the developer's review of 3 Nov 2026 (ADR 0021, D67):

- Unfolded in the Library, the field spans the screen between its margins,
  as on Home and a studyset: it fell short on the right, by the padding
  around the two folded buttons, which now stands only around those.
- Who answers stands right before the buttons at the right, which no longer
  shift as its name changes (Claude Haiku, Claude Opus): it fills the space
  left, aligned to its end, rather than a share of it.
- Every button of the field and of a conversation's follow-up is boxed, a
  tile a shade above the field with rounded corners, as Claude's apps have
  them; who answers too.
- On a studyset with a licence, the unfolded field takes its usual place
  over the licence's line rather than squeezing in above it; folded, its
  row still keeps clear of the line.

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

apps/learn/halkyon_learn_flutter/test/feature/assistant/assistant_field_test.dart

@@ -465,6 +465,53 @@ void main() {
     debugDefaultTargetPlatformOverride = null;
   });
 
+  for (final (where, location) in [
+    ('Home', RoutePaths.home),
+    ('the Library', RoutePaths.library),
+    ('a studyset', RoutePaths.studyset('japanese')),
+  ]) {
+    testWidgets('unfolded on $where, the field spans the width between the '
+        "screen's margins, as wide on the right as on the left (the "
+        "developer's review of 3 Nov 2026)", (tester) async {
+      await showApp(tester, location: location);
+      await unfold(tester);
+      final field = tester.getRect(find.byType(AssistantField));
+      expect(field.left, closeTo(16, 0.01));
+      expect(field.right, closeTo(400 - 16, 0.01));
+    });
+  }
+
+  testWidgets('on a studyset with a licence, the folded button keeps clear '
+      'of its line; unfolded, the field takes its usual place over it rather '
+      "than squeezing in above it (the developer's review of 3 Nov 2026)", (
+    tester,
+  ) async {
+    studysets.receiveRemoteChange(
+      'japanese',
+      encodeStudysetPayload(
+        StudysetContent(
+          title: 'Japanese',
+          description: RichContent.empty(),
+          license: 'CC-BY-SA-4.0',
+          licenseHolder: 'Tae Kim',
+          licenseYear: 2026,
+        ),
+      ),
+    );
+    await showApp(tester, location: RoutePaths.studyset('japanese'));
+    final licence = find.textContaining('Tae Kim', findRichText: true);
+    final line = tester.getRect(licence);
+    expect(
+      tester.getRect(find.byTooltip('Search the web')).bottom,
+      lessThan(line.top),
+      reason: 'folded, clear of the line',
+    );
+
+    await unfold(tester);
+    final field = tester.getRect(find.byType(AssistantField));
+    expect(field.bottom, greaterThan(tester.getRect(licence).top));
+  });
+
   testWidgets("a studyset's name is never offered to go into a web search", (
     tester,
   ) async {

apps/learn/halkyon_learn_flutter/test/feature/assistant/conversation_test.dart

@@ -316,6 +316,60 @@ void main() {
     );
   });
 
+  testWidgets('the buttons right of who answers stay where they are '
+      'whatever its name, and every button of the field is boxed, as '
+      "Claude's (the developer's review of 3 Nov 2026)", (tester) async {
+    assistants.offer = AssistantsOffer(
+      assistants: [
+        _claude(),
+        OfferedAssistant(
+          id: 'opus',
+          name: 'Claude Opus, thinking longer',
+          protocol: 'anthropic',
+          host: 'api.anthropic.com',
+          model: 'claude-opus',
+          agreedAt: _agreed,
+        ),
+      ],
+    );
+    await showApp(tester);
+    Rect at(String tooltip) => tester.getRect(
+      find.descendant(
+        of: find.byType(AssistantField),
+        matching: find.byTooltip(tooltip),
+      ),
+    );
+    final history = at('Conversations');
+    final speak = at('Speak your question');
+    final field = tester.getRect(find.byType(AssistantField));
+    expect(field.right - speak.right, lessThan(16), reason: 'at the right');
+
+    await openPicker(tester);
+    await tester.tap(find.text('Claude Opus, thinking longer').last);
+    await tester.pumpAndSettle();
+    expect(find.text('Ask Claude Opus, thinking longer…'), findsOneWidget);
+    expect(at('Conversations'), history);
+    expect(at('Speak your question'), speak);
+
+    for (final icon in [
+      LucideIcons.plus,
+      LucideIcons.history,
+      LucideIcons.mic,
+    ]) {
+      final button = tester.widget<IconButton>(
+        find.descendant(
+          of: find.byType(AssistantField),
+          matching: find.widgetWithIcon(IconButton, icon),
+        ),
+      );
+      expect(
+        button.style?.backgroundColor?.resolve({}),
+        isNotNull,
+        reason: '$icon boxed',
+      );
+    }
+  });
+
   testWidgets("an answer's Copy stands beneath it, its icon in line with "
       "the answer's text", (tester) async {
     await showApp(tester);
@@ -750,7 +804,8 @@ void main() {
     await unfold(tester);
     await choose(tester, ['Studyset: Diary']);
 
-    await ask(tester, 'What is this about?');
+    // Short: the test's wide font would hang the text's handle over Ask.
+    await ask(tester, 'About what?');
 
     expect(find.text(warning), findsOneWidget);
     expect(find.textContaining('to api.anthropic.com'), findsOneWidget);
@@ -758,7 +813,7 @@ void main() {
     await tester.tap(find.text('Cancel'));
     await tester.pumpAndSettle();
     expect(assistants.asked, isEmpty);
-    expect(find.text('What is this about?'), findsOneWidget);
+    expect(find.text('About what?'), findsOneWidget);
 
     assistants.answers.add(_says('Your diary.'));
     await tester.tap(