Constant LEGACY_DEFAULT_CONTEXT_BUDGET 

pub const LEGACY_DEFAULT_CONTEXT_BUDGET: usize = UNCONFIGURED_CONTEXT_WINDOW_FALLBACK; // 32_000usize

Historical proactive context budget used when an operator sets neither an absolute budget nor the opt-in model-relative ratio.

Shares its value with UNCONFIGURED_CONTEXT_WINDOW_FALLBACK — the legacy default budget was exactly the unconfigured-window stub — but is a distinct concept: this is a proactive-trim budget default, not a model-capacity fallback. Kept as a named alias so the two never drift and each call site reads as the concept it means.