gate(ROCM): M4 -- pinned vLLM-ROCm oracle on gfx1100 + ROCm device-golden lane in the Qwen3-0.6B near-tie gate

[VikashLoomba]

M4 on gfx1100 — the pinned vLLM-ROCm oracle + the ROCm near-tie gate lane (issue #41)

This PR lands the M4 milestone for BACKEND-ROCM: a pinned vLLM-ROCm oracle built on the same box (the maintainer's assignment — this is the only board that can host one) and the ROCm arm of the existing device-golden lane in the Qwen3-0.6B near-tie gate.

The oracle

• Upstream vLLM at the parity pin 555967922, runtime identity 0.23.1rc1.dev1511+g555967922 (verified == .agents/upstream-sync.md parity-pin block)
• Built from source as a ROCm wheel for gfx1100 in rocm/vllm-dev:base (2,696 files; _C/_rocm_C/_moe_C ABI extensions present)
• Committed image vllm-rocm-oracle:555967922-gfx1100; full recipe in .agents/specs/rocm-m4-oracle.md
• K=10 per-prompt greedy capture: deterministic in every (prompt,pos) cell — a well-posed strict gate on this board

The gate result (Qwen3-0.6B, 4x RX 7900 XTX, ROCm 7.14)

correctness gate: 16/16 prompts PASS  (STRICT token-exact: 11/16;
near-tie-band only: 5/16; max gap 0.125 nats @ prompt[3] tok=1;
0 forward-divergent) — 125/125 assertions
BACKEND PROOF — Qwen3-dense ops on device type 5 with 0 declines
(kPagedAttention selections=7168)

All 28 token-divergent positions vs the oracle's own greedy are inside the 0.5-nat band. The known p0 France/Italy flip is a literal 0.0000-nat tie in the oracle's own logits — the Metal M3b signature, reproduced on ROCm: vLLM's teacher-forced argmax on our exact prefix IS 15344 (" Italy").

Change shape (additive only)

• tests/parity/test_qwen3_paged_engine.cpp: the existing Metal/Tenstorrent device-golden branch gains the kROCM arm — identical anchor + near-tie-band logic, ROCm's own oracle-backed golden pair; CUDA/CPU/Metal/TT behaviour byte-unchanged
• New goldens: our_ids_rocm.npy, neartie_gap_mnats_rocm.npy (the lane pair) + greedy_ids_rocm.npy/greedy_dist_rocm.npy (oracle capture evidence). dgx base goldens untouched
• .agents/specs/rocm-m4-oracle.md: the reproducible recipe
• Records: coordination claim CLAIM-ROCM-M4, parity-ledger row, STATUS.md, NOW.md

Next (not in this PR)

Qwen3.5-0.8B (GDN) and the 35B keep-quant gates under the same oracle; Qwen3-4B strict deterministic gate needs disk.