* Fix pcl-aqb.1: eliminate function-pointer cast UB in start_thread() via union
Replace the single void* run field in thread_data with a union
{ thread0_run run0; thread1_run run1 } so each function pointer is
stored and retrieved at its correct type, eliminating the
thread0_run <-> thread1_run cast chain UB. Split start_thread() into
prun_thread() and prun_thread1() that each populate the appropriate
union member, backed by a shared start_thread_common() helper. Add
malloc NULL check with error log in both public functions.
pthread_create failure handling (log + free) was already present.
Ref GH #199.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
* Add prun start_thread() resource-leak and UB tests (pcl-aqb)
8 test cases using linker interposition covering pthread_create
failure data-free, attr_destroy on failure, malloc failure graceful
return, union fn storage without cast, and success path accounting.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Co-authored-by: Levi Neely <lkn@darkstar.example.net>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
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