fix(learn): a passage's gaps flow inside its text

A passage was a Wrap of a Text per part between gaps. A Wrap places whole
children, so a part longer than a line took the width to itself, and every
gap and the text after it started a line of its own. One Text.rich with each
gap a WidgetSpan wraps the text as one paragraph, the gaps standing in it.

Whats-New: Fill-in-the-blank passages read as running text, their gaps inside the lines.
Whats-New-De: Lückentexte lesen sich als fortlaufender Text, die Lücken stehen in den Zeilen.

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/lib/src/feature/learning_path/widget/exercise_views.dart

@@ -339,26 +339,38 @@ class const FillInTheBlankView({
           ),
         ),
         const SizedBox(height: 12),
-        Wrap(
-          crossAxisAlignment: WrapCrossAlignment.center,
-          runSpacing: 8,
-          children: [
-            for (var gap = 0; gap < exercise.gaps; gap++) ...[
-              Text(parts[gap], style: theme.textTheme.bodyLarge),
-              DragTarget<String>(
-                onAcceptWithDetails: (details) => fill(gap, details.data),
-                builder: (context, candidates, _) => _Gap(
-                  word: words[gap],
-                  highlighted: candidates.isNotEmpty,
-                  mark: markOf(grade, gap, picked: words[gap] != null),
-                  onTap: words[gap] == null
-                      ? null
-                      : () => onChanged([...words]..[gap] = null),
+        // One paragraph with the gaps standing in its lines: a Wrap of a
+        // Text per part gave a long part the width to itself, and put each
+        // gap, and the text after it, on a line of its own.
+        Text.rich(
+          TextSpan(
+            style: theme.textTheme.bodyLarge,
+            children: [
+              for (var gap = 0; gap < exercise.gaps; gap++) ...[
+                TextSpan(text: parts[gap]),
+                WidgetSpan(
+                  alignment: PlaceholderAlignment.middle,
+                  child: Padding(
+                    // Room above and below, so a gap on one line doesn't
+                    // touch a gap on the next.
+                    padding: const EdgeInsets.symmetric(vertical: 4),
+                    child: DragTarget<String>(
+                      onAcceptWithDetails: (details) => fill(gap, details.data),
+                      builder: (context, candidates, _) => _Gap(
+                        word: words[gap],
+                        highlighted: candidates.isNotEmpty,
+                        mark: markOf(grade, gap, picked: words[gap] != null),
+                        onTap: words[gap] == null
+                            ? null
+                            : () => onChanged([...words]..[gap] = null),
+                      ),
+                    ),
+                  ),
                 ),
-              ),
+              ],
+              TextSpan(text: parts.last),
             ],
-            Text(parts.last, style: theme.textTheme.bodyLarge),
-          ],
+          ),
         ),
         const SizedBox(height: 16),
         Wrap(

apps/learn/halkyon_learn_flutter/test/feature/learning_path/widget/path_screens_test.dart

@@ -948,6 +948,47 @@ void main() {
     expect(find.text('Correct!'), findsOneWidget);
   });
 
+  testWidgets('a passage is one paragraph, its gaps standing in its lines; '
+      'a filled gap tapped gives its word back', (tester) async {
+    final paths = repository();
+    final id = await paths.createPath(
+      'japanese',
+      LearningPathContent.titled('Particles'),
+    );
+    await paths.createStep(
+      id,
+      StepKind.fillInTheBlank,
+      step(
+        StepKind.fillInTheBlank,
+        'Fill in',
+        const FillInTheBlank(passage: '私___学生です。', blanks: ['は']),
+      ),
+    );
+    await showApp(tester, RoutePaths.path('japanese', id));
+    final passage = find.byWidgetPredicate(
+      (widget) =>
+          widget is RichText && widget.text.toPlainText().startsWith('私'),
+    );
+
+    expect(passage, findsOneWidget);
+    expect(
+      (tester.widget<RichText>(passage).text as TextSpan).toPlainText(),
+      contains('学生です。'),
+      reason: 'the text after the gap is in the same paragraph',
+    );
+
+    final inPassage = find.descendant(of: passage, matching: find.text('は'));
+    await tester.tap(find.widgetWithText(ActionChip, 'は'));
+    await tester.pumpAndSettle();
+    expect(inPassage, findsOneWidget);
+    expect(find.text('は'), findsOneWidget, reason: 'gone from the words');
+
+    await tester.tap(inPassage);
+    await tester.pumpAndSettle();
+    expect(inPassage, findsNothing);
+    expect(find.text('は'), findsOneWidget, reason: 'back among the words');
+  });
+
   testWidgets('sorts items by tapping one and then its category', (
     tester,
   ) async {