fix(todo): quick add highlights a word while the keyboard still composes it

On Android, keyboards with suggestions (Gboard) and Japanese ones keep
the word being typed composing until a space. The title's controller
fell back to the plain composing span whenever a composing range was
set, so "today" lit up only after the space or once the keyboard
closed. It now always draws the tokens' highlight, cut where a token or
the composing range starts or ends, with the composing underline on top
where they overlap.

Whats-New: Add task highlights dates and other words as you type them, not only after a space.
Whats-New-De: „Aufgabe hinzufügen“ hebt Daten und andere Wörter schon beim Tippen hervor, nicht erst nach einem Leerzeichen.

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/todo/halkyon_todo_flutter/lib/src/feature/task/widget/quick_add_sheet.dart

@@ -700,7 +700,10 @@ class const QuickAddButton({
   }
 }
 
-/// The title's controller, its [tokens] highlighted.
+/// The title's controller, its [tokens] highlighted, also while the
+/// keyboard still composes them: Android's keyboards (Gboard with
+/// suggestions, Japanese ones) compose the word typed until a space, and a
+/// plain composing span had hidden its highlight until then.
 class _TokenController() extends TextEditingController {
   List<QuickAddToken> tokens = const [];
   Color? highlight;
@@ -712,37 +715,51 @@ class _TokenController() extends TextEditingController {
     required bool withComposing,
     TextStyle? style,
   }) {
+    final shown = [
+      for (final token in tokens)
+        if (token.end <= text.length) token,
+    ];
     final composing =
         withComposing &&
-        value.isComposingRangeValid &&
-        !value.composing.isCollapsed;
-    if (tokens.isEmpty || composing) {
-      return super.buildTextSpan(
-        context: context,
-        style: style,
-        withComposing: withComposing,
-      );
+            value.isComposingRangeValid &&
+            !value.composing.isCollapsed
+        ? value.composing
+        : null;
+    if (shown.isEmpty && composing == null) {
+      return TextSpan(style: style, text: text);
     }
     final marked = TextStyle(
       backgroundColor: highlight,
       color: onHighlight,
     );
+    const underlined = TextStyle(decoration: TextDecoration.underline);
+    // Split where a token or the composing range starts or ends.
+    final cuts = <int>{
+      0,
+      text.length,
+      for (final token in shown) ...[token.start, token.end],
+      if (composing != null) ...[composing.start, composing.end],
+    }.toList()..sort();
     final children = <TextSpan>[];
-    var from = 0;
-    for (final token in tokens) {
-      if (token.end > text.length) {
-        break;
-      }
-      if (token.start > from) {
-        children.add(TextSpan(text: text.substring(from, token.start)));
-      }
-      children.add(
-        TextSpan(text: text.substring(token.start, token.end), style: marked),
+    for (var i = 0; i + 1 < cuts.length; i++) {
+      final from = cuts[i];
+      final to = cuts[i + 1];
+      final inToken = shown.any(
+        (token) => token.start <= from && to <= token.end,
+      );
+      final inComposing =
+          composing != null && composing.start <= from && to <= composing.end;
+      children.add(
+        TextSpan(
+          text: text.substring(from, to),
+          style: switch ((inToken, inComposing)) {
+            (true, true) => marked.merge(underlined),
+            (true, false) => marked,
+            (false, true) => underlined,
+            (false, false) => null,
+          },
+        ),
       );
-      from = token.end;
-    }
-    if (from < text.length) {
-      children.add(TextSpan(text: text.substring(from)));
     }
     return TextSpan(style: style, children: children);
   }

apps/todo/halkyon_todo_flutter/test/app/todo_app_test.dart

@@ -1463,6 +1463,43 @@ void main() {
         expect(stored.single.content?.date, isNull);
       });
 
+      testWidgets('a token is highlighted while the keyboard still composes '
+          'it, the composing underline over it (Gboard, Japanese IMEs)', (
+        tester,
+      ) async {
+        await start(tester, usedBefore: true);
+        await goTab(tester, 'Inbox');
+        await tester.tap(find.byTooltip('Add task'));
+        await tester.pumpAndSettle();
+        await tester.showKeyboard(find.byKey(quickAddTitleKey));
+        const text = 'Pay rent today';
+        tester.testTextInput.updateEditingValue(
+          const TextEditingValue(
+            text: text,
+            selection: TextSelection.collapsed(offset: text.length),
+            composing: TextRange(start: 9, end: text.length),
+          ),
+        );
+        await tester.pumpAndSettle();
+
+        final field = find.byKey(quickAddTitleKey);
+        final span = tester
+            .widget<TextField>(field)
+            .controller!
+            .buildTextSpan(
+              context: tester.element(field),
+              withComposing: true,
+            );
+        final today = span.children!.cast<TextSpan>().singleWhere(
+          (child) => child.text == 'today',
+        );
+        expect(today.style?.backgroundColor, isNotNull, reason: 'highlighted');
+        expect(today.style?.decoration, TextDecoration.underline);
+        final rest = span.children!.cast<TextSpan>().first;
+        expect(rest.text, 'Pay rent ');
+        expect(rest.style?.decoration, isNull);
+      });
+
       testWidgets('a chip picked takes its token out of the title; the down '
           'arrow and the + open the description', (tester) async {
         await start(tester, usedBefore: true);