F418 full-gate concurrency audit

initial_execution=LLVM17 full lit with default 192-worker fanout
initial_result=287 passed, 2 unsupported, 1 failed out of 290 tests
initial_failure=test_qf_bv_campaign.py
initial_observation=QF_BV conformance artifact was reported invalid
initial_raw_log_sealed=yes
isolated_rerun=1 passed, 0 failed
final_execution=LLVM17 full lit with controlled 8-worker fanout
final_result=288 passed, 2 unsupported, 0 failed out of 290 tests
f418_focused_both_versions=3 passed, 0 failed per version
interpretation=the isolated pass and controlled complete pass identify concurrency sensitivity in an existing QF_BV campaign, not an F418 regression
claim_boundary=this chronology does not identify one proven root cause for the initial artifact rejection