ZJIT: make test-spec: Crash in Process.warmup: "rb_assert_cme_handle:!rb_objspace_garbage_object_p(handle)"

[XrXr]

As of 2026-01-23 (HEAD 7c75dbe), when running the full test-spec suite with ZJIT enabled and --repeat 2, the test runner crashes during Process.warmup:

https://github.com/Shopify/ruby/blob/7c75dbe51e/spec/ruby/core/process/warmup_spec.rb#L6-L9

The assertion failure is:

../jit.c:491: Assertion Failed: rb_assert_cme_handle:!rb_objspace_garbage_object_p(handle)

Reproducer:

make -s test-spec RUN_OPTS= MSPECOPT=--debug 'SPECOPTS=-T --zjit-call-threshold=2 --repeat 2'

The crash seems reproducible but does NOT reproduce when running warmup_spec.rb in isolation.

See also: ruby#15220