Constant CACHE_RAM_LOW_WATERMARK_BYTES 

pub const CACHE_RAM_LOW_WATERMARK_BYTES: u64 = _; // 4_294_967_296u64

Threshold below which a working prompt cache counts as cramped.

At or below this the cache holds too few conversations to reliably survive switching between them, so a resumed conversation will often re-prefill from scratch. Sits above CACHE_RAM_FLOOR_BYTES, so it describes a cache that is working but tight — not one that was switched off.