docs(frank-archon): the slab is a slope, and the ceiling was mine not the engine's

Measured A/B on the shipped pair 25600/5120: A-cold 43.5k prefill 3,290 ->
3,584 t/s (+8.9 %) and the 3-way 197k aggregate 3,051 -> 3,589 t/s (+17.6 %,
wall 193.7 -> 164.5 s). The prediction I shipped with the arm -- slab is a
threshold below ~26 GiB, so 1,600 MiB buys ~0 -- is falsified by the measurement
it asked for. Two slab points inside noise of EACH OTHER (22,208 / 24,000) are
not a plateau. The cliff is above 25,600: 26,071 measured 4,379 t/s.

Ceiling re-derived from the engine's own budget table (card 32,624 MiB, pair at
29,120 settling 2,058 MiB free against its 209.19 MiB floor => 30,969 claimable).
The 29,120 bound was my 1 GiB \`keep free\` reserve; the seam now derives the
number, so the next resize starts from the engine's arithmetic.

Ledger for the record: slab 16,235 -> 17,548 slots while the pinned host pool
hands the same experts back (8,893 -> 7,580) -- the transfer is the mechanism,
the pinned pool is the slow path. Capacity contract live-verified at 3 slots:
3 x 199,984-token prompts accepted (599,952 tokens), fourth refused as too
large to ever fit.

Probe law learned: the oversized-prompt refusal names the prompt's token count
BEFORE prefill (free calibration) and fires on prompt tokens ALONE, not on
prompt + max_tokens; the window is ~514,286 chars at 2.5714 chars/token.

scripts/frank-archon.env

@@ -194,12 +194,19 @@ FRANK_ARCHON_GPU_HEADROOM_MIB=96
 # contract), so the boot ledger's `backs N sequences all at 200000 tokens at
 # once` line is the referee for THIS pair and the concurrent probe is its
 # regression test.
-# FALSIFIABLE CLAIM for the 25,600 arm: today measured slab 22,208 -> 3,397
-# t/s and 24,000 -> 3,290 t/s at 43.5k single-stream, so below ~26 GiB the slab
-# is a THRESHOLD, not a slope. Expected: +1,600 resident expert slots, ~0
-# prefill. The point that DOES move prefill is 26,071 (the 2026-10-11 fp8 arm,
-# 4,379 t/s), fundable only by dropping to two slots. Prefill moving more than
-# +-3 % on this arm falsifies the threshold reading.
+# VERDICT on the 25,600 arm (measured 2026-10-13, scripts/probe-frank-archon-kv.py):
+# the threshold claim is FALSIFIED — the slab is a SLOPE at this end. A-cold
+# 43.5k single-stream: 22,208 -> 3,397, 24,000 -> 3,290, 25,600 -> 3,584 t/s;
+# the 3-way 197k arm's aggregate prefill 3,051 -> 3,589 t/s (wall
+# 193.7 -> 164.5 s). So +1,600 MiB of slab = +8.9 % single-stream and
+# +17.6 % concurrent, both outside the +-3 % noise floor. The 22,208/24,000
+# pair landed inside noise of EACH OTHER, which is what made it read as a
+# plateau; two points are not a curve.
+# The cliff that remains is between 25,600 (3,584) and 26,071 (4,379, the
+# 2026-10-11 fp8 control at seqs 3 / pool 3,543) — +22 % for +471 MiB. At THREE
+# slots that is only reachable by breaking the ceiling (26,112 + 5,120 = 31,232
+# vs 30,969, ~214 MiB above the engine's floor); at TWO slots it is free:
+# pool 3,072 + slab 27,897 = exactly the ceiling, slab above the cliff.
 FRANK_ARCHON_VRAM_WEIGHTS_MIB=25600
 FRANK_ARCHON_VRAM_KV_MIB=5120
 # KV cache QUANTIZED (fp8). This engine's flag takes ONLY bf16|fp8 — there is