I left some comments on the PR.  We can at least make it detect musl libc and improve its default behavior there.

FWIW CPython's recursionlimit and the C stack have long been a thorn in the side of many things.

Even when Python's thread_pthread.h is changed to set a better default when running under musl libc, there are still plenty of ways to run into problems.  ex: Extension modules can create threads on their own that then call back into CPython.  So can C/C++ code that embeds a Python interpreter.  Those choose their own stack sizes.  When they choose low values, surprising crashes ensue for people working on the Python side...

As a feature (beyond just this issue): It'd be ideal to actually be able to introspect the C stack space remaining and issue a RecursionError whenever it falls below a threshold.  Rather than just blindly using a runtime adjustable number that any Python code can tweak to allow crashes via `sys.setrecursionlimit()`.  Other languages like Golang use a dynamic stack and allocate more on SIGSEGV.

[meta/off-topic: Why does anyone use small thread stack sizes? This is often done to save virtual address space in applications that expect to have thousands of threads. It matters a lot less on 64-bit address space. But there are reasons...]