Lowering the session trigger must not replace the window-relative lean selection budget with threshold times target_ratio. Invalidate the lean cache through the existing property while preserving explicit legacy and external-engine fallback behavior. Narrow adaptation of the aux-sync diagnosis and invariants in #93576, without adding a required recalibration method to context engines. Related: #95681, #93576 Co-authored-by: Turgut Kural <58116817+TurgutKural@users.noreply.github.com>