docs: record DSpark single-slot switch + ROCm parallel crash (2026-08-15) across KB; refs AGENTS/deployment/benchmark/matrix/index

docs/frank-default-large-benchmark.md

@@ -7,10 +7,19 @@ llama.cpp build on that machine (upstream, b10133+).
 ## Summary
 
 - **Backend**: ROCm (HIP). Vulkan is not viable for the full pipeline.
-- **Spec (2026-08-14)**: MTP sidecar drafter (`draft-mtp`, `a4lg/Qwen3.6-27B-MTP-ONLY-Q8_0.gguf`, `--spec-draft-n-max 3`). Replaced DFlash, which was retired because it releases a generating slot prematurely under parallel load (see below).
-- **Context**: 3 parallel slots x 200700 (pool 602100).
+- **Spec (2026-08-15)**: DSpark sidecar draft (`draft-dspark`,
+  `magnitudedev/Qwen3.8-27B-DSpark-GGUF` Q8_0, 1.36B, `--spec-draft-n-max
+  7`). Replaced bundled MTP. **Single-slot (PARALLEL=1)** because DSpark
+  crashes the ROCm backend under two concurrent 16k prompts (see
+  [[qwen3.8-spec-matrix]]).
+- **Context**: 1 slot x 262144.
 - **KV**: `q8_0` K / `q8_0` V on GPU.
-- **Batch**: 8192 / ubatch 8192 (2026-08-14, uses the VRAM headroom; peaks ~65.5 GiB of 96 GiB).
+- **Batch**: 8192 / ubatch 256.
+
+> The A/B tables below are retained for history but predate the 2026-08-14
+> Qwen3.8-27B `UD-Q8_K_XL` switch to bundled MTP and the 2026-08-15 DSpark
+> switch.  The current production spec decision and the DSpark parallel crash
+> are recorded on [[qwen3.8-spec-matrix]].
 
 ## 2026-08-14: Spec A/B (ROCm, production config, default sampling, 1.1k-token prompt)