# Issue 109: compiled verification gates

Qwen target forwards inside the MTP loop now carry the pinned MTPLX
`decode_verify` phase through attention, eager HC injection, captured-prefix
repair and final-primary commit. Draft/history and ordinary prefill/AR retain
their existing phase. Compiled layer replay keys include the phase to prevent
reuse of a graph with the other gate law.

The BF16 attention gate compiles exactly
`output * sigmoid(gate.astype(f32).astype(bf16))`; the casts select the fused
lowering and do not move the sigmoid to F32. F32 uses its separate compiled
expression; FP16 remains standalone. The existing native Rust graph compiler
and Metal execution implement these expressions. No global sigmoid, compiler
math flags, DS4/GLM implementation, or shared family helper changed.

Two actual eager `GatedResidual._verify_inject` calls also demonstrated a
phase/site failure (the adjacent `active-hc-sites.jsonl` records inputs and both
outputs). That sibling therefore satisfies this issue's explicit scope rule:
its verify-only divide/sigmoid/multiply now compiles as pinned MTPLX does.
Unrelated PLE/shared-expert gates remain unchanged. This is oracle parity, not a
new DS4Server feature or a full fixed-M4 verifier.

Persisted MTP snapshots without the new gate policy are rejected before
restoration; old AR snapshots remain compatible. Tests use both a constructed
old manifest and an actual pre-fix MTP file, and verify failed restoration leaves
the current live state intact. New checkpoints reproduce resident warm state
exactly after reset/reopen.

## Verification and boundaries

The pinned oracle is MTPLX `9882703f3105363ddc37eca9f97aa09a1d387112`
with MLX 0.32.2. The installed Bare-Speed artifact and hardware are recorded in
`../issue104-ar/environment.json`.

- Exhaustive finite BF16 (65,280) and FP16 (63,488), plus 65,536 dense F32
  gate values, compare every output byte in all three phases. BF16 also covers
  all three HC-injection phases. The owned original `active_attention_gate`
  and `bf16_gate` regressions require the corrected expression and neighbors.
- Real cold/warm MTP requests compare each target forward's input IDs and all
  logits/hidden bytes, generated tokens, cache offsets, final logits/hidden and
  trunk/MTP state arrays. Native resident and disk-reopened full state hashes
  must agree exactly.
- The complete final-primary test covers greedy/sampled, depths 1–3,
  stop/max-token termination and failure/cancellation controls.
- Existing whole-attention fixtures exercise both TF32 modes and prepared/lazy
  input routes; hyper fixtures control the unchanged non-verify route.

The real-model comparison explicitly sets the oracle's
`MTPLX_QWEN4_VERIFY_SDPA_HEAD_CHUNK=0` to isolate this gate change with the same
attention consumer. Independent default-oracle comparison exposed a missing
head-chunked consumer before the gate, tracked separately in
[#113](https://git.rfc1437.de/hugo/DS4Server/issues/113). This controlled run does
not establish default-route model parity. `default-route-mismatch.jsonl`
retains the evidence.

Cache receipts retain raw hashes as well as value hashes with zero signs
canonicalized. A first-position prefill key has one signed-zero bit difference;
this is reported explicitly rather than hidden by a tolerance, and is tracked
separately in [#114](https://git.rfc1437.de/hugo/DS4Server/issues/114). Target outputs,
final logits/hidden and resident-versus-reopened state use raw byte exactness.

All four mandatory gates and serial Metal/oracle checks are listed in
`checks.json`. These are correctness receipts, not performance measurements.

## Reproduction

```sh
local-eval-results/mtplx-reference-env-0.32.2/bin/python \
  tools/issue109-gate-reference.py /path/to/pinned/mtplx /tmp/issue109-gate
cargo test --all-features --bin ds4-server --no-run
cargo build --bin test-supervisor
export DS4_ISSUE109_GATE=/tmp/issue109-gate
# Resolve TEST_EXECUTABLE from cargo; run Metal processes serially.
target/debug/test-supervisor 4096 60 120 --command TEST_EXECUTABLE \
  issue109_gate_phase_and_dtype_laws --ignored --nocapture --test-threads=1
export MTPLX_CONTEXT_COPY=0
export DS4_QWEN38_ARTIFACTS=/path/to/model
export DS4_ISSUE109_DIR=/tmp/issue109-product
export DS4_ISSUE109_OLD=/path/to/pre-fix-mtp-checkpoint
target/debug/test-supervisor 114688 60 120 --command TEST_EXECUTABLE \
  issue109_verify_rows_and_warm_checkpoint --ignored --nocapture --test-threads=1
MTPLX_QWEN4_VERIFY_SDPA_HEAD_CHUNK=0 \
  local-eval-results/mtplx-reference-env-0.32.2/bin/python \
  tools/issue109-model-reference.py /path/to/pinned/mtplx \
  "$DS4_QWEN38_ARTIFACTS" "$DS4_ISSUE109_DIR" /tmp/issue109-model-oracle
```