--vram-elastic (the config's "vram_elastic": true) allocates the expert cache as one
reserved address range backed by physical segments (CUDA virtual memory management,
512 MiB each, --vram-segment-mib), so every slot keeps its address. Between
requests, the engine command `VRAM <reserve_mib>` gives the last segments back to
the driver until that much VRAM is free (their experts become CPU misses, the prompt
path's loan moves down and its chunk shrinks to fit), or maps them again and puts
the same experts back when more is free. `VRAM` alone: the start's reserve. The
server's POST /v1/vram {"reserve_mib": N | null} sends it after a running request,
keeps it for an engine that is unloaded, and /v1/status shows the cache's size.
Never automatic. One NVIDIA GPU only (no layer split, helper caches, --peer-device
or the resident low-RAM mode); HIP refuses the flag.
RTX 5070, Q2_0 (4.8 GiB cache): reserve 6000 -> 4.3 GiB freed in 78 ms, decode
44 -> 33 tok/s; grown back in 92 ms, the answers token for token the ones before.
Without the flag the cache is the one cudaMalloc it was (same answers with and
without the flag until a VRAM command).
