Sub::Quote deferred subs lose identity across threads

Start with t/sub-quote-threads.t and reproduce it on both commands shown for the JVM and interpreter backends. Read Sub/Defer.pm around line 75 and its CLONE implementation, then trace deferred-sub references and %DEFERRED across thread creation. Done means quoted and deferred subs retain their identity and the focused regression test passes on both backends.

Summary

Sub::Quote 2.006009 fails when quoted/deferred subs are retrieved or invoked from PerlOnJava threads. The failure reproduces on both the JVM and interpreter backends.

Reproduction

The CPAN random tester record is:

2026-09-18 07:06:07 FAIL Sub::Quote Sub::Defer ... 5430 5435 5/5435 subtests failed; 1/15 test programs failed

The failing test is:

t/sub-quote-threads.t

Using the built distribution with its library and test-library paths:

timeout 120 ./jperl -I<build>/blib/lib -I<build>/t/lib <build>/t/sub-quote-threads.t
timeout 120 ./jperl --interpreter -I<build>/blib/lib -I<build>/t/lib <build>/t/sub-quote-threads.t

Both backends fail identically: 5 of 6 assertions fail. The only passing assertion is the unquoted One case. Quoted/deferred sub retrieval and execution return undef, including the two-thread cases.

The complete CPAN run has 14 of 15 test programs passing; only t/sub-quote-threads.t fails. PerlOnJava also emits:

Use of uninitialized value in hash element at .../Sub/Defer.pm line 75

Expected behavior

System Perl passes the complete oracle run: 7036/7036 tests, including t/sub-quote-threads.t.

Technical analysis

Sub::Defer::undefer_sub looks up deferred-sub metadata in %DEFERRED using the deferred sub reference. Sub::Defer provides a CLONE implementation specifically to repair stringified subreference keys after threading.

On PerlOnJava, the lookup at Sub/Defer.pm line 75 receives an undefined or otherwise non-matching key after the thread boundary. This indicates that thread cloning is not preserving or remapping the identity/metadata of deferred quoted subs as required by Sub::Defer::CLONE.

The issue is present in both execution backends, so it appears to be shared runtime/thread-cloning behavior rather than a JVM-backend-only problem or a module-specific compilation issue.

Impact

Non-threaded Sub::Quote functionality passes, but applications using quoted/deferred subs from Perl threads can silently receive undef or fail to invoke the intended subroutine. This is a compatibility bug affecting modules that use Sub::Quote together with threads.

Suggested investigation

1. Trace cloning of the deferred sub reference and the %DEFERRED metadata across thread creation.
2. Compare PerlOnJava's handling of CLONE and stringified subreference keys with system Perl.
3. Add a focused project-owned regression test covering quote_sub, quoted_from_sub, unquote_sub, and deferred-sub invocation from a child thread on both backends.