Profiling showed the 2-slot rotation stalls ~5.5ms per layer waiting for
the down_exps upload: 3 tensors per MoE layer need 3 slots for a full
layer of lookahead. Default is now 3 (one layer), configurable via the
env var value, degrading to however many slots fit on OOM.
Also fixes a use-after-free: on a failed slot regrow the repointed
staging tensors kept dangling pointers into freed device memory, which
graph reuse carried into later evals. Staging repoints are now restored
right after kernel launch, slots are sized once from the graph max, and
allocation happens before freeing.
Qwen3.6-35B-A3B pp2048 on RTX 3060: 1643 -> 1880 t/s (mainline: 1143).
thecodacus
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