test(BACKEND-ROCM): reconcile the Strix full-suite failures

Row: BACKEND-ROCM

The operator's HIP full-suite gate for PR #3010 is unresolved. Strix lease d7a790d5-158e-46d8-9e32-1284f4c41a6c recorded 18 failed targets and then lost its host to a reboot at 741/745 completed tests. It supplies no completed full-suite verdict. Issues #3066 and #3068 own the diffusion fixture failures; this issue owns the remaining 17 targets and the required baseline pairing.

The failed targets fall into these groups:

• test_qwen3_dflash2_draft, test_dflash2_runner_reach, test_dflash2_concurrency, test_dflash2_ctx_capacity, and test_dflash2_prefix_cache: explicit missing ROCm IndexSelect; host reference fallback is refused because device memory is not host-addressable.
• test_dflash2_exl3_reach and test_dflash2_draft_phase_trace: caught exceptions and missing draft outputs; the log does not print their exception text, so the operation cause is not established.
• test_mtp_depth: explicit missing CausalConv1dSpecUpdate, plus an async-capability expectation that needs separate diagnosis.
• test_qwen4_exp_gguf_load_plan, test_qwen4_exp_gguf_weights, and test_qwen4_exp_runner: ROCm keep-quant/gather expectations or explicit refusal. #2394 owns missing block-decoding gather arms; #1940 owns broader I-quant coverage.
• test_placement_reach and test_engine_scratch_steady_state: fixtures appear to assume CPU placement or a CPU pool while the runtime selects ROCm. This is not yet a runtime-paired diagnosis.
• test_loaded_engine_dense and test_llm_engine: expected async scheduling/multiple concurrent batches, but the ROCm backend does not advertise sampled-token readback support.
• test_cuda_quant_dot: a CUDA-named residency fixture routes through CurrentPlatform() and expects formats not admitted by ROCm.
• test_glm_moe_dsa_forward: explicit missing ROCm DsaIndexerLogits; the related W2 source/spec and historical closed issues need reconciliation.

The affected tests and relevant registration, loader, and runner sources are byte-identical between main 08a34c3a74d78046f83886f242d07110a70ff45e and sampling repair 2bd0ca67f051d7ef7d48b52ad75a8729fe30d0b3. That is supporting evidence only. None of these 17 targets has a paired main runtime result in the supplied log.

Next gate: reproduce each target on pinned main under the same leased device, build, environment, and serial scheduling. Capture omitted exception text in diagnostic scratch. Then distinguish test-fixture assumptions from actual missing backend capabilities, and assign each required implementation to its owning row/spec before changing code. A change in another row is not authorized merely to make this report green.

Do not enable unsafe managed allocation to hide missing native operations. Do not expand keep-quant tables to bypass residency refusals. Do not call this a passing or narrowly waived gate. Local evidence remains /tmp/pr3010-full-lease.log; the separate focused sampling tests do not replace this full-suite obligation.

Start with /tmp/pr3010-full-lease.log and reproduce the listed targets on pinned main using the same leased device, build, environment, and serial scheduling. Capture the omitted exception text in diagnostic scratch and pair each target with a main runtime result. Done means distinguishing fixture assumptions from missing ROCm capabilities and assigning each required implementation to its owning row or spec.