TaskGroup's task's exception's participate in a reference cycle, via TaskGroup.create_task -> task -> exception and loop.create_task -> task -> exception

[graingert]

Bug report

Bug description:

the following test fails when run with eager tasks

 async def test_exception_refcycles_parent_task(self):
 """Test that TaskGroup deletes self._parent_task"""
 tg = asyncio.TaskGroup()
 exc = None

 class _Done(Exception):
 pass

 async def coro_fn():
 async with tg:
 raise _Done

 try:
 async with asyncio.TaskGroup() as tg2:
 tg2.create_task(coro_fn())
 except* _Done as excs:
 exc = excs.exceptions[0].exceptions[0]

 self.assertIsInstance(exc, _Done)
 self.assertListEqual(gc.get_referrers(exc), no_other_refs())

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-128552: fix refcycles in eager task creation #128553
• [3.13] gh-128552: fix refcycles in eager task creation (#128553) #128585
• [3.12] gh-128588: gh-128550: gh-128552: fix refcycles in eager task creation (#128553) and remove eager tasks optimization that missed and introduced incorrect cancellations (python#129063) #128586