The previous commit's doubling was a silent no-op. HALOGEN_KV_POOL_FIT
measured the device budget at startup and lowered the pool straight back
to 262144, while the deploy still reported healthy in 12s.
The engine's arithmetic: 121 GiB host - 67.7 resident weights - 24.0
reserved for the n-gram page cache and the OS = 29.5 GiB of device
budget, and that single budget carries the KV pool AND the prefill arena.
At HALOGEN_MAX_TOK=32768 the arena is ~20.6 GiB, so 524288 positions
need 35.0 GiB against 29.5 available.
HALOGEN_MAX_TOK=16384 halves the arena to ~10.5 GiB, bringing the
524288 need to ~24.9 GiB, which fits with ~3 GiB of margin. Cost is
about 8-9% of prefill throughput, per upstream. This is the engine's own
prescribed fix, quoted verbatim in its refusal message.
Lowering HALOGEN_CTX was the other option the engine offered; rejected
because both clients declare 262144 as the context window, so it would
break the client contract rather than pay for the pool.
Frank
c489b204ea