fix(BACKEND-ROCM): diagnose the gfx1100 Qwen3 paged anchor drift

[VikashLoomba]

Row: BACKEND-ROCM

The unchanged gfx1100 HIP build at 760c8dd7e27781430b909c3679790c52fe332182
fails the ordinary Qwen3-0.6B paged gate and its KV-boundary case.
Both fail the device-specific anchor check at
tests/parity/test_qwen3_paged_engine.cpp:365.

Prompt 1 is Once upon a time,. At zero-based generated position 9,
the engine emits token 264 and the committed ROCm anchor expects 279.
The selected anchor is our_ids_rocm.npy, not the CPU/CUDA anchor.
Both cases stop at this anchor assertion before any later near-tie check.
The boundary case fails before its separate boundary exercise.

The operator reproduced the result on the original HIP library and a clean
baseline worktree. The baseline executable SHA256 is
08e3bbc5c53a09bc2e0a2fc9d710303deab86975eedec706fdbaa81e60fb23b8.
It reports 4 cases, 2 failed cases, and 72 passing assertions out of 74.
The F16 implementation reports the identical errors and assertion counts.
All 19 paired existing HIP failures match individually across that change.
This establishes that the observed failure predates #3092. It does not
establish whether the model execution, artifact selection, or anchor is wrong.

This differs from #3102, which records CPU prompt 0, position 5, tokens
15344 versus 9625. It also differs from #269, which records a gfx1200
failure with the lowercase-France prompt. #3070 owns 17 other full-HIP
failures and their Strix baseline pairing; that measurement remains separate.

The operator used the supplied local RX 7900 XTX host, serial CTest,
HIP_VISIBLE_DEVICES=0,1, ROCR_VISIBLE_DEVICES=0,1,
VT_OP_PROVIDER_STATS=1, and VT_CUDA_GRAPH_DEDUP=0, under the GPU mutex.
The exact command, library and executable hashes, clean source identity,
logs, and comparison are retained under
/home/vikash/vllm.cpp-rdna3-f16-impl/build-rocm-f16-evidence/full-hip-baseline-v1/:
command.json, operator-input-audit.json, operator-run.log,
operator-receipt.json, and operator-comparison.json.
The baseline log SHA256 is
abd5ec9157b4e3d553782d2251348dc23eeb70dc4374586359d21fd271a627cb.

The backend row owes an artifact-matched diagnosis against the active oracle
and a reviewed correction. Preserve the current anchor assertion, fixtures,
and tolerances during diagnosis. Do not refresh the golden solely to make
this gate green. The F16 row records this unresolved baseline failure under
its own Owed section without expanding its implementation scope.