feat(frank-dragoon): raise HALOGEN_CTX to the native 262144 ceiling

The 200,704 ceiling squeezed the harness contextWindow down to 155,648
(the 400-zone fit law needs ~45k of gap under the ceiling), which is why
long dragoon sessions kept hitting the 400 zone: the harness clamps
max_tokens to window - est - 4096, its chars/4 est under-counts ~3 %,
and config.yml compacts at 95 % while the pair was designed for 85 %.

Ceiling -> checkpoint's native 262,144 (no RAM move: the KV pool stays
401,408 and is what the ledger bills; the band ctx <= pool <= slots*ctx
still holds). The harness window becomes 200,000 with a 62,144 gap.

The fit-law seam now reads the declared window from the vault page (the
one owner) and checks the arithmetic at the live 95 % trigger, so a
ceiling/window pair that drifts back together fails tests/run.sh
instead of a live session.

scripts/frank-dragoon.env

@@ -49,14 +49,21 @@ FRANK_DRAGOON_TOKENIZER_FILES="tokenizer.json chat_template.jinja tokenizer_conf
 # stays at the image default, which is what was qualified) ------------------
 # Served id. OpenWebUI api_configs model_ids for the :7770 backend MUST name it.
 HALOGEN_MODEL_ID=frank-dragoon
-# PER-REQUEST ceiling: a longer prompt is a 400 naming the limit, never a
-# truncation. The harness window must sit ~45k UNDER this (the 400-zone law on
-# the page) — a window equal to the ceiling makes every long request a 400.
-HALOGEN_CTX=200704
-# ONE pool behind both slots, sized so BOTH can carry a maximum-length request
-# at once. Pool positions buy concurrency; the per-request window never moves
-# with them. Legal band: ctx <= pool <= slots * ctx (the seam enforces it), and
-# RAM the pool takes is RAM the n-gram table's page cache loses.
+# PER-REQUEST ceiling, set to the checkpoint's NATIVE window (262,144 — a
+# longer prompt is a 400 naming the limit, never a truncation; stretching
+# past native would need HALOGEN_ROPE_YARN and is not on plan). The harness
+# `contextWindow` must sit ~45k under THIS number (the 400-zone law on the
+# page): with the window at 200,000 the gap is 62,144, which absorbs the
+# chars/4 under-count. A window at or near the ceiling makes every long
+# request a guaranteed 400.
+HALOGEN_CTX=262144
+# ONE pool behind both slots. The harness window is 200,000, so 401,408
+# still carries TWO maximum harness-length conversations at once
+# (2 x 200,000 + one 45,056 budget <= pool + cap headroom); two literal
+# ceiling-length requests would queue instead — buying those means raising
+# the pool, and RAM the pool takes is RAM the n-gram table's page cache
+# loses. Pool positions buy concurrency; the per-request window never moves
+# with them. Legal band: ctx <= pool <= slots * ctx (the seam enforces it).
 HALOGEN_KV_POOL_POSITIONS=401408
 # Two concurrent conversations: the MTP drafter is not slot-locked on this
 # engine, so the second slot is capacity, not a speculation tax.