while documenting i realized that we need a separate takeTask method. previously i thought that we could just leverage the assignTask method for that. but taking a task also involves a check that the task is currently unassigned.
e.g. if 2 people see a task in their takable task list, then the second one that clicks on 'Take' should get an error.
in contrast, reassignment doesn't need that check.
so we need to separate methods for take and assign.
