docs(frank-archon): reconcile the runbook with the live 1.8.1 two-slot shape

The endpoint moved to radiance 1.8.1 with MAX_SEQS=2 and the
--vram-weights-mib/--vram-kv-mib pair removed (PR #30); env, serve script and
bats carried the new shape while the page and the AGENTS.md block still
described the 1.0.13 3-slot era, so every point-of-use number was wrong.

Re-derived from the live checkout and the 2026-10-19 11:10 boot ledger, not
from the stale pre-#31 draft: runtime block (digest, version oracle, the two
CLI breaks that are boot refusals), shape table (demand-signal rows, derived
VRAM split, restored spec/batch row, host-only prefix tier, step sharing),
container contract (no /data mount), the measured 2-slot ledger, a new Eras row
for the retired 1.0.13 era whose rollback is a digest plus a trio rewrite, and
the laws: pool sizing and the per-card budget re-scoped to the pair era, a new
resolver law (funds ~90% of the worst case, host RAM below a slab step is inert,
MAX_SEQS is a demand signal), the sludge law marked measured-at-3-slots with the
fix ordered-not-verified, the knob-availability law flipped, and the slots law
now pricing the third slot in KV (4.20 -> 2.76 GiB).

AGENTS.md

@@ -462,12 +462,15 @@ disagrees with it is the bug.
 - Owns: `scripts/frank-archon.env`, `scripts/serve-frank-archon.sh`,
   `scripts/frank-archon.service`, `scripts/ttm-preflight.sh`, template
   `scripts/qwen38-froggeric-v22.5.jinja`; image digest-pinned
-  `stilldeadcode/radiance@sha256:4c3f4845…`; container name = unit name.
-- Shape: TP=2 over `wht6`, `--max-num-seqs 3`, `--max-model-len 200000`,
-  `expert_tiered` placement, 44,928 MiB pinned host pool per rank, VRAM pair
-  `--vram-weights-mib 25600 --vram-kv-mib 5120` (ONE budget: weights + kv ≤
-  30,969 MiB/card), `fp8` KV, MTP depth 2, MNBT 2048, prefix cache 8 GiB host
-  + 64 GiB disk, n-gram table pinned to RAM.
+  `stilldeadcode/radiance@sha256:d590e300…` (radiance 1.8.1); container name = unit name.
+- Shape: TP=2 over `wht6`, `--max-num-seqs 2`, `--max-model-len 200000`,
+  `expert_tiered` placement, 44,928 MiB pinned host pool per rank, `fp8` KV,
+  MTP depth 2, MNBT 2048, `--busy-prefill-chunk auto`, prefix cache 8 GiB host
+  tier only, n-gram table pinned to RAM. The per-card weights/KV split is derived
+  by the engine's budget resolver from `--gpu-headroom-mib`, the cache bound and
+  the host pool; the `--vram-weights-mib`/`--vram-kv-mib` pair and the prefix disk
+  tier are gone (removed at 1.3.0 / 1.8.1) and naming either is a boot refusal,
+  not a no-op.
 - Harness/gate contract: `models.yml` `contextWindow` MUST quote 200,000
   (over-length is refused, never truncated); the ~147 GiB pinned-RAM ledger
   is why this is a root unit, and `ttm-preflight.sh` raises