PEP 810: re-entrant lazy from-import raises ImportCycleError even when the name exists

On CPython 3.15.2 and 3.16.0a1: q/a.py is lazy from q.b import B then USES = B; q/b.py is class B: pass then from q.a import *. Importing q.a raises ImportCycleError: cannot import name 'q.b.B'. Resolving B starts importing q.b, and q.b's star import touches q.a's still-pending placeholder for B. The per-thread 'placeholder already being resolved' check raises, although q.b.B is already defined; the eager version works. It happens with the explicit lazy keyword in normal mode and with plain imports under -X lazy_imports=all. In the wild, antlr4-python3-runtime 4.13.2 (from antlr4 import *, pygrun) hits it. Diagnose by checking whether the name exists on the target module just before the failing line. Workaround: keep that import eager with sys.set_lazy_imports_filter, or avoid star-importing a module that has pending lazy names from inside the module those names point to.