perf(ds4): optimize q5 fused verifier on AMD

[davide221]

Summary

• add the AMD q=5 fused DSpark verifier path
• support exact partial-rejection rollback across both compressor boundaries
• keep five-row dense projections on MMVQ and use the qualified gfx1201 x4+1 ROCmFP4 path
• add deterministic context-sweep tooling and unit coverage
• pin the JSON fallback to an immutable source archive so builds avoid the flaky release-asset route

This is the first PR in the heterogeneous DeepSeek 4 performance stack.

Validation

Tested on an R9700 target with Strix Halo expert offload, four routed experts, q=5, and deterministic 128-token completions.

Context	Previous median	Fused q=5 median
2K	64.212 tok/s	67.957 tok/s
4K	62.428 tok/s	65.927 tok/s
8K	59.267 tok/s	62.544 tok/s
16K	53.750 tok/s	56.335 tok/s
2K after 16K	63.804 tok/s	67.458 tok/s

All 25 measured responses matched the expected SHA-256. The DeepSeek 4 GPU unit suite passed.

Reproduction

Run harness/qualification/deepseek4/qualify_ds4_q5_amd.sh with TARGET_MODEL, DRAFT_MODEL, and HOTNESS_CSV. The qualifier records configuration, response hashes, timings, ROCm state, and memory use.

[cubic-dev-ai]

All reported issues were addressed across 16 files

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[cubic-dev-ai]

All reported issues were addressed across 16 files (changes from recent commits).

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[cubic-dev-ai]

All reported issues were addressed across 7 files (changes from recent commits).

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