Track marked shipped 2026-06-17. All 6 verification criteria evaluated
with PASS/EXCEEDED/READY status and notes. 7 pre-existing test failures
documented with root cause and pre_existing_failures_remaining flag.
Risk register updated: scope_creep=none, behavior_change=none,
doc_drift=medium (error_handling.md deprecation section required
surgical rewrite to historical note).
No deferred_to_followup_tracks (this track completed cleanly).
