perf(gfx12): disable slow default DFlash verify graph

[HUSRCF]

Summary

Disable the default DFlash verifier HipGraph route for gfx1201 + MQ4G256.

Paired long-context runs on an R9700 showed the captured verifier graph slower than the direct tiled-flash verifier path. The graph remains available through the explicit diagnostic opt-in:

HIPFIRE_VERIFY_GRAPH=1

Other architectures and quantization shapes retain their existing behavior.

Which surface(s) does this touch?

• serve — speculative DFlash verifier routing
• arch crate(s): hipfire-arch-qwen35

Implementation

dflash_verify_graph_env_eligible() is default-off only for gfx1201 + MQ4G256. Explicit behavior remains:

• HIPFIRE_VERIFY_GRAPH=0: force graph off
• HIPFIRE_VERIFY_GRAPH=1: diagnostic graph opt-in

The direct batched tiled-flash verifier path remains enabled.

Tests

• cargo test -p hipfire-arch-qwen35 --lib dflash_verify_graph_env -- --nocapture
• cargo build --release -p hipfire-cli -p hipfire-daemon
• Full 6-request thinking E2E on local R9700 / gfx1201
• max-seq=32768, max-tokens=1024, approximately 11.5K-token prompts
• HIP_VISIBLE_DEVICES=0
• Qwen3.6 27B MQ4 + DFlash MQ4

E2E result:

turns=6 runaway=0 empty=0 retrieval_miss=0
avg_prefill=594.0 tok/s avg_decode=48.4 tok/s
per-request decode: 61.2, 67.8, 11.7, 63.2, 72.9, 13.3 tok/s

All requests completed with finish=stop; no attractor or empty-output failures were reported.

Battery output: /tmp/hf693-gfx12-latest-e2e.json

Graph opt-in validation

A separate one-request run with HIPFIRE_VERIFY_GRAPH=1 confirmed:

[verify-graph] warmup for B=16 complete
[verify-graph] captured for B=16 with 1154 blobs

The opt-in request produced the same output identity as the default route (request_md5=8460b63690bf124ed759f90efdb777f3, 299 tokens, tau=4.84, finish=stop).

Artifacts

daemon md5: 5340f68e16e91548eec4a47eddd49948
target sha256: 86a5f80fd29d545abb1093dead242725ced6d68b8607c6d566d897b1a82442dc
draft sha256: bd8c4f07ae80fe1385bf2606af9a7ba0daa18ca8daec50916f2a489054c44e70

{"routes":[{"mode":"battery","tag":"qwen3.6:27b"}],"claim":"On gfx1201 with Qwen3.6 27B MQ4 DFlash, the legacy MQ4 verifier Graph is disabled by default while the direct tiled-flash verifier remains active; HIPFIRE_VERIFY_GRAPH=1 still captures the diagnostic graph."}