feat(calendar): list due tasks from a task vdir beside the events

The sampler reads open VTODOs with a due date from
~/.local/share/tasks/<list>/*.ics (a vdirsyncer filesystem storage,
override with UDT_TASKS_DIR) and writes them to the cache as ISO
'task' lines. The card merges them into the week's rows by date, with
a checkbox before the title and an urgency colour: overdue critical,
due today warning, later label. Overdue tasks stay until done, so they
lead the table. Tasks never mark the month grid.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/test/test_data.lua b/test/test_data.lua
index c33e5ae..9612c43 100644
--- a/test/test_data.lua
+++ b/test/test_data.lua
@@ -117,6 +117,22 @@ assert(#up == 2 and up[2].d == 25, 'eight days from the 18th end on the 25th')
 assert(#data.calendar_upcoming({ { y = 2026, m = 11, d = 2 } },
   { 2026, 10, 28 }, 8) == 1, 'week crosses into next month')
 
+-- Tasks: separate from events so the grid stays appointments-only, merged
+-- with them by date for the table. An overdue task is kept (it sorts first),
+-- one past the week is cut like an event, and an all-day row sorts before a
+-- timed one on the same day, as khal orders them.
+assert(#cal.tasks == 3, 'task count, got ' .. tostring(#cal.tasks))
+assert(cal.tasks[1].task and cal.tasks[1].start == nil
+  and cal.tasks[2].start == '17:00', 'task fields')
+local ag = data.calendar_agenda(cal, { 2026, 9, 18 }, 8)
+local titles = {}
+for i, e in ipairs(ag) do titles[i] = e.title end
+assert(table.concat(titles, ',') == 'Overdue chore,A birthday,Dentist,'
+  .. 'Task due today,Team sync | notes',
+  'agenda order, got ' .. table.concat(titles, ','))
+assert(#data.calendar_agenda(empty, { 2026, 9, 18 }, 8) == 0,
+  'no events, no tasks: empty agenda')
+
 -- month_shape: September 2026 has 30 days and starts on a Tuesday.
 -- Monday = 1, so Tuesday = 2.
 local ndays, first = data.month_shape(2026, 9)