The old test asserted that a non-MiniMax provider returning a generic
overflow (no provider-reported max) would step down to the 128K probe
tier. The salvaged fix from #33673 deliberately removes that step-down
because guessed tiers cause configured 1M sessions to silently shrink.
Update the test to assert the new contract: keep the configured 200K
window and rely on compression instead.
321ce94e25