_activate_batch_root_subtasks flipped a held root-subtask to team=MAIN_PM
but left task_type=code (intake only coerces main_pm-team drafts, so a
board-routed code root reached activation still code-typed). The
main_pm+code combo re-introduces the 2026-06-27 meltdown. Mirror
approve_and_start's own retype via main_pm_cannot_own_code so the
activated child is a planning-typed coordination root.
TDD: RED test_activate_batch_root_subtasks_retypes_code_to_planning
watched fail (task_type stayed CODE), then GREEN after the retype.
ruff+mypy clean; 125 batch/umbrella/approve tests green, no regressions.
