Locks down the contract that becomes the primary path for residence
detail in Phase 3:
- filters _allTasks by residenceId
- returns empty shell for residence with no tasks (vs null for cache miss)
- returns null when _allTasks itself is null (caller must hit API)
Catches re-introduction of the conditional _tasksByResidence write
branch removed in the previous commit. The per-residence cache is
deprecated; updateTask must only mutate _allTasks.
Captures gitea#2 at the cache layer. Three tests:
- updateTask_seedsAllTasks_whenCacheIsEmpty (the core bug)
- updateTask_distributesAcrossColumns_whenSeedingThenAdding
- updateTask_replacesExistingTaskById_acrossColumns
All three FAIL on this commit because updateTask is a conditional
?.let{} that no-ops when _allTasks is null. Phase 1 fix in the next
commit makes them green.
Trey t