Foundation document for the future test_infra_hardening track that
will address session-scoped live_gui fixture isolation, silent
__getattr__/__setattr__ contract assumptions, and similar test
infrastructure fragility.
Also documents the test_rag_phase4_final_verify batch failure
that surfaces after the __getattr__ fix unblocks
test_full_live_workflow. The RAG test failure is NOT a regression
- it reproduces on pre-fix HEAD too. It's a pre-existing test
isolation issue (the live_gui fixture is session-scoped, so state
from the 4 sims pollutes the controller).
