feat: sort tasks by due time

frontend/src/lib/task-utils.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { buildTaskRrule, defaultTaskDueAt, filterTasks, groupTaskTree, moveItemWithinScope, parseTaskRrule, renderMarkdown, toDateTimeLocal } from './task-utils'
+import { buildTaskRrule, classifyTaskForToday, defaultTaskDueAt, filterTasks, groupTaskTree, isSameTaskSortTier, moveItemWithinScope, parseTaskRrule, renderMarkdown, toDateTimeLocal } from './task-utils'
 
 type SearchTask = {
   id: string
@@ -33,6 +33,25 @@ describe('task utilities', () => {
     expect(groupTaskTree([parent])).toEqual([{ task: parent, subtasks: [child] }])
   })
 
+  it('classifies due edits for Today membership', () => {
+    const start = new Date('2026-09-10T00:00:00+08:00')
+    const end = new Date('2026-09-11T00:00:00+08:00')
+    expect(classifyTaskForToday({ completed: false, due_at: '2026-09-09T12:00:00+08:00' }, start, end)).toBe('overdue')
+    expect(classifyTaskForToday({ completed: false, due_at: '2026-09-10T12:00:00+08:00' }, start, end)).toBe('today')
+    expect(classifyTaskForToday({ completed: false, due_at: '2026-09-11T12:00:00+08:00' }, start, end)).toBe('outside')
+    expect(classifyTaskForToday({ completed: true, due_at: '2026-09-09T12:00:00+08:00' }, start, end)).toBe('outside')
+  })
+
+  it('only allows manual movement within the same completion and deadline tier', () => {
+    const noDueOpen = { completed: false, due_at: null }
+    expect(isSameTaskSortTier(noDueOpen, { completed: false, due_at: null })).toBe(true)
+    expect(isSameTaskSortTier({ completed: false, due_at: '2026-09-10T08:00:00Z' }, { completed: false, due_at: '2026-09-10T08:00:00Z' })).toBe(true)
+    expect(isSameTaskSortTier({ completed: false, due_at: '2026-09-10T08:00:00Z' }, { completed: false, due_at: '2026-09-10T16:00:00+08:00' })).toBe(true)
+    expect(isSameTaskSortTier(noDueOpen, { completed: false, due_at: '2026-09-10T08:00:00Z' })).toBe(false)
+    expect(isSameTaskSortTier(noDueOpen, { completed: true, due_at: null })).toBe(false)
+    expect(isSameTaskSortTier({ completed: false, due_at: '2026-09-10T08:00:00Z' }, { completed: false, due_at: '2026-09-11T08:00:00Z' })).toBe(false)
+  })
+
   it('moves an item before or after another item without changing other scopes', () => {
     const rows = [
       { id: 'a', parent_id: null },