Phase-switched loading trades bytes for lower latency

v0.42.0 - Phase-switched loading trades bytes for lower latency

Sixth completed delivery in the authorized four-to-eight course. The 40.671-second
CPU-first OPT-2.7B FP16 screen passes every frozen component gate. All checked
logits match dense streamed FP16 exactly, including both candidate warmups; all
48 scored tokens per condition agree under the same 4800 MiB allowance.

Dense prefill plus exact scalar-decode packets takes 2.545918 s versus 3.223919 s
for always-packet: 21.0303% less whole-episode time and 42.0176% less prefill call
time, while buying 26.1433% MORE outgoing bytes. The cost is explicit. Against
dense streaming, it saves 90.6293% of outgoing H2D and 63.2498% of episode time.
All three modes have the same sampled GPU peak: 4,763,783,168 B (about 4543 MiB).

Protocol,
results and inspirations,
compact receipts,
source freeze.

Known 512-token inputs, 16-token continuations, alternating candidate order and a
baseline-first reference. Whole-episode gain is 0.678001 s: 0.348921 s is in forward
call intervals and 0.329080 s outside them, including recording/episode overhead.
Calls still include in-call recording; this is not trace-free production timing.
Cold shared-worker-to-first DENSE logit is 13.085643 s, not phase-first cold TTFT.
Host copies, staging, workspace, KV, readback, dispatch and records are charged.

No hidden full GPU preload, precision/KV transition, statistical omission or llama.cpp
patch. No new holdout, task-quality, physical-small-card OOM, unique-access, optimized
Q4/Q8, independently resident 2.7B, or deployable-runtime claim. Historical LRU,
forecast and uniform-prefill failures remain failures; this measures a new policy.

All 662 CPU tests and historical raw replays pass; source review and repeat audit
are approved/exact. Raw phase-v042-raw.zip: 79,147,215 B, 160 members, SHA256
97ff97efbbb79923c79f12a60ef09666c7dc4dba4caff1b512c3bdc2efb39f19.
Archive restored/hash checked; final clean-tip full-suite evidence attaches separately.
No model weights redistributed. Prose uses normal spacing; published history and
frozen protocols were not rewritten to clean up older formatting.

Complete #57, not
milestone 10.
Stop this course at six deliveries. Qualified low-bit baselines, instrumentation
overhead and broader context/workload behavior remain open, each requiring a new
short protocol. No automatic long matrix or native pivot.