frank-medium: pay for DSpark's draft KV with a 38:27 split

DSpark declares no sliding window, so its draft context -- built with
n_ctx = llama_n_ctx(ctx_tgt) -- caches the whole target window: 5 layers x 2 x 8
kv heads x 128 dim x 2 B = 20 KiB/position, i.e. 5.0 GiB at 262144, where
DFlash2's sliding_window 2048 cost ~40 MiB. At a 1:1 split that put ROCm1 at
33.9 GB of 34.2 GB and the first draft graph capture died inside
common_speculative_impl_draft_dflash::process with "ROCm error: out of memory"
-- after the model had loaded and /health had answered, which is why the deploy
looked like a crash-loop rather than a sizing failure.

Handing three target layers to ROCm0 restores headroom on both cards at the full
window. Measured at 262144: 28.52 GB / 30.71 GB, i.e. 5.30 GiB and 3.26 GiB free
(was 2.7 GB free on the draft-carrying card with 1:1 + DFlash2). The unit seam
now models the busier card as a skewed share plus the drafter's full-context KV,
calibrated to the rocm-smi figure.

AGENTS.md gains the durable lesson: read sliding_window out of the drafter's
GGUF header before sizing a spec-decode deployment.

scripts/frank-medium.env

@@ -41,7 +41,9 @@
 #
 # Drafter: magnitudedev/Qwen3.8-27B-DSpark-GGUF @ Q8_0, 1.27 GiB: 5 layers,
 # hidden 5120, block-diffusion proposal with the Markov head (dspark).
-# Decoding stays lossless -- the target verifies every drafted token.
+# Decoding stays lossless -- the target verifies every drafted token. Its KV
+# spans the whole context (see SIZING): unlike DFlash2 it declares no sliding
+# window, and that is what the tensor split below pays for.
 #
 # Architecture (GGUF arch qwen35): 64 layers as 16 x (3 x (Gated DeltaNet ->
 # FFN) + 1 x (Gated Attention -> FFN)) -- 48 linear-attention layers whose
@@ -51,12 +53,13 @@
 # state at any depth.
 #
 # SIZING, measured (rocm-smi, 2026-09-16).  Weights split across the two cards;
-# the drafter rides the second.  The loader's compute buffers are part of what
-# is seen below -- they are allocated at load, not per request:
+# the drafter AND its KV ride the second.  The loader's compute buffers are part
+# of what is seen below -- they are allocated at load, not per request:
 #
-#   CTX_SIZE   GPU 0        GPU 1        headroom on the busier card
-#   131072     19.89 GB     24.30 GB     9.9 GB / 31 %
-#   262144     24.72 GB     29.14 GB     5.07 GB / 15 %   <- deployed
+#   CTX_SIZE  split  GPU 0      GPU 1      headroom on the busier card
+#   131072    1,1    19.89 GB   24.30 GB   9.9 GB / 31 %   (DFlash2)
+#   262144    1,1    24.72 GB   29.14 GB   5.07 GB / 15 %  (DFlash2) <- before
+#   262144    38,27  28.52 GB   30.71 GB   3.50 GB / 10 %  (DSpark)  <- deployed
 #
 # 262144 is the window the model ships (n_ctx_train) and it fits with room, so
 # the fleet gets the whole thing; the arithmetic that used to cap this endpoint
@@ -64,6 +67,16 @@
 # adds VRAM (a longer drafter, quantized KV, more slots) re-read the numbers
 # rather than assuming, and prefer CTX_SIZE over --gpu-layers.
 #
+# WHY THE SPLIT IS 38:27.  The draft context is built with `n_ctx =
+# llama_n_ctx(ctx_tgt)` (common/speculative.cpp), so the drafter's KV scales
+# with the target window, and DSpark -- unlike DFlash2, which declared
+# sliding_window 2048 and cost ~40 MiB -- caches all of it: 5 layers x 2 x 8 kv
+# heads x 128 dim x 2 B = 20 KiB per position, i.e. 5.0 GiB at 262144.  At a
+# 1:1 split that put ROCm1 at 33.9 GB of 34.2 GB and the draft's first graph
+# capture died with `ROCm error: out of memory` (in
+# common_speculative_impl_draft_dflash::process).  Handing three target layers
+# to ROCm0 buys back ~3 GiB of headroom on both cards at the full window.
+#
 # WARNING: do not name any variable TEMP, HOST, or GPU_MAX_HEAP_SIZE (HIP reads
 # those bare vars; 2026-08-13 incident).  llama.cpp takes --host/--port/--temp
 # as flags only.
@@ -88,8 +101,11 @@ LISTEN_PORT=7770
 HIP_VISIBLE_DEVICES=0,1
 DEVICES=ROCm0,ROCm1
 SPLIT_MODE=layer
-# Empty = distribute layers by free VRAM (equal here, so 1,1 by hand).
-TENSOR_SPLIT=1,1
+
+# Skewed 38:27 rather than 1:1: ROCm1 also carries the drafter and the whole of
+# its KV, so it must hold fewer target layers for the cards to end level.  See
+# SIZING above -- this is measured, not computed.
+TENSOR_SPLIT=38,27
 
 NGL=999
 # Auto-fit has no business resizing a context we set explicitly.