Validates one task from a task list (initial or iteration): must not contain Output; only allowed field names; required keys must be present. Appends to issues when invalid. Call only after List.fill_names has been run (during parsing, before this); this method only reads the task name for issue messages and does not inject or set names.
When phase is REFINEMENT, Name is not required (overlay keeps the existing task name). Label for messages uses section + name or
slug via task_label.
Used by parse_task_list and parse_task_list_iteration so both paths share the same rules.
| t |
the task to validate (its task_data keys are checked) |
| phase |
markdown phase; REFINEMENT skips Name requirement |