feat(todo): the Plan beside Upcoming, with what has no date (ADR 0033, D34)

Upcoming's 3-day grid gets the Plan Today's calendar has, through what
the two tabs now share (PlanHost). Its new last group holds the open
tasks of no day, so a week can be planned from the Inbox by dropping them
on an hour; they aren't counted on the button, which says what is due.

Whats-New: Upcoming's 3-day view has the Plan too, and tasks without a date can be dragged from it onto any day.
Whats-New-De: Auch die 3-Tage-Ansicht unter Demnächst hat den Plan, und Aufgaben ohne Datum lassen sich von dort auf jeden Tag ziehen.

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/test/app/todo_app_test.dart

@@ -36,6 +36,7 @@ import 'package:halkyon_todo_flutter/src/tabs/hour_grid.dart';
 import 'package:halkyon_todo_flutter/src/tabs/plan_panel.dart';
 import 'package:halkyon_todo_flutter/src/tabs/today_icon.dart';
 import 'package:halkyon_todo_flutter/src/tabs/today_tab.dart';
+import 'package:halkyon_todo_flutter/src/tabs/upcoming_tab.dart';
 import 'package:halkyon_todo_flutter/src/tabs/week_strip.dart';
 import 'package:halkyon_ui/halkyon_ui.dart';
 import 'package:intl/intl.dart';
@@ -1133,6 +1134,44 @@ void main() {
         expect(find.text('Far'), findsOneWidget);
       });
 
+      testWidgets('its Plan shows in 3-day alone; a task of no date dropped on '
+          "a later day's hour gets that day and time (D34)", (tester) async {
+        await start(tester, usedBefore: true);
+        await seed(
+          tester,
+          TaskContent(title: 'Someday', projectId: inbox()),
+        );
+        await goTab(tester, 'Upcoming');
+        expect(find.byKey(UpcomingTab.planKey), findsNothing);
+        await threeDay(tester);
+        expect(find.byKey(UpcomingTab.planKey), findsOneWidget);
+        tester.view.physicalSize = const Size(1400, 900);
+        await tester.pumpAndSettle();
+        expect(find.text('No date'), findsOneWidget);
+
+        final today = Day.of(DateTime.now());
+        final row = tester.getCenter(find.text('Someday'));
+        final column = tester.getTopLeft(
+          find.byKey(HourGrid.columnKey(today.plus(1))),
+        );
+        final gesture = await tester.startGesture(row);
+        await tester.pump(kLongPressTimeout + const Duration(milliseconds: 50));
+        final to = column + const Offset(30, 11 * 60 + 5);
+        for (var step = 1; step <= 10; step++) {
+          await gesture.moveTo(Offset.lerp(row, to, step / 10)!);
+          await tester.pump(const Duration(milliseconds: 16));
+        }
+        await gesture.up();
+        await tester.pumpAndSettle();
+
+        final date = (await tester.runAsync(
+          () => tasks().all(),
+        ))!.single.content!.date!;
+        expect(date.day, today.plus(1));
+        expect(date.time, inInclusiveRange(10 * 60 + 30, 11 * 60 + 30));
+        expect(date.time! % 15, 0);
+      });
+
       testWidgets(
         'a click adds a task at that quarter hour, for half an hour',
         (tester) async {

apps/todo/halkyon_todo_flutter/test/feature/task/task_views_test.dart

@@ -135,6 +135,7 @@ void main() {
     expect(plan.toPlan.map((t) => t.id), ['open']);
     expect(plan.timed.map((t) => t.id), ['eight', 'nine']);
     expect(plan.count, 4);
+    expect(plan.noDate.map((t) => t.id), ['undated']);
 
     final home = planOf(tasks, today, projectIds: {'home'});
     expect(home.overdue, isEmpty);
@@ -142,4 +143,35 @@ void main() {
     expect(home.timed.map((t) => t.id), ['eight']);
     expect(home.count, 2);
   });
+
+  test('the Plan keeps the tasks of no day apart, uncounted (D34)', () {
+    const today = Day(2026, 11, 5);
+    OpenTask task(String id, {String? parentId, bool completed = false}) => (
+      id: id,
+      content: TaskContent(
+        title: id,
+        projectId: id == 'other' ? 'home' : 'inbox',
+        parentId: parentId,
+        completedAt: completed ? DateTime(2026, 11, 4) : null,
+      ),
+    );
+    final tasks = [
+      task('free'),
+      task('other'),
+      task('sub', parentId: 'free'),
+      task('done', completed: true),
+    ];
+
+    final plan = planOf(tasks, today);
+    expect([for (final task in plan.noDate) task.id], ['free', 'other']);
+    expect(plan.count, 0);
+    expect(plan.isEmpty, isFalse);
+    expect(
+      [
+        for (final task in planOf(tasks, today, projectIds: {'home'}).noDate)
+          task.id,
+      ],
+      ['other'],
+    );
+  });
 }