frank-large: EXPERIMENT - raise HALOGEN_MAX_TOK to 65536

Operator call, measuring what the prefill arena actually costs against
upstream's do-not-raise warning. Rollback is one revert: the settled
config was 16384, which made the 524288 pool fit at 26.6 GiB.

dankclaw/frank-large/quadlet/frank-large.container

@@ -104,17 +104,20 @@ Environment=HALOGEN_CTX=262144
 # used to contend for one 262k pool.
 Environment=HALOGEN_KV_POOL_POSITIONS=524288
 Environment=HALOGEN_KV_SLOTS=4
-# LOAD-BEARING. This line is what makes the doubling above real; do not
-# "clean it up". The device budget here is 121 GiB - 67.7 resident weights
-# - 24.0 reserved for the n-gram page cache and the OS = 29.5 GiB, and that
-# one budget carries BOTH the KV pool and the prefill arena. At the upstream
-# HALOGEN_MAX_TOK=32768 the arena is ~20.6 GiB, so 524288 positions need
-# 35.0 GiB against 29.5 available and HALOGEN_KV_POOL_FIT silently lowers
-# the pool back to 262144 — the deploy still reports healthy, so the
-# regression is invisible unless you read the ledger. Halving the arena to
-# ~10.5 GiB brings the 524288 need to ~24.9 GiB, which fits with ~3 GiB
-# of margin, at about 8-9% of prefill throughput.
-Environment=HALOGEN_MAX_TOK=16384
+# EXPERIMENT 2026-09-12 (operator call): raised to 65536 to measure what the
+# arena actually costs, against upstream's warning that it "sizes a ~4 GB
+# scratch arena, so do not raise it to the native context".
+#
+# Background on why this line matters at all. The device budget here is
+# 121 GiB - 67.7 resident weights - 24.0 reserved for the n-gram page cache
+# and the OS = 29.5 GiB, and that ONE budget carries both the KV pool and the
+# prefill arena. Measured arena-side cost ("everything but the pool"):
+#   max_tok 16384 -> 12.2 GiB   (524288 pool fits: 26.6 total)
+#   max_tok 32768 -> 20.6 GiB   (524288 pool REFUSED at 35.0, fit lowers to 262144)
+# HALOGEN_KV_POOL_FIT only ever LOWERS, never raises, and never below
+# HALOGEN_CTX — and the deploy still reports healthy either way, so the pool
+# you asked for is not necessarily the pool you got. Read the `kv pool:` lines.
+Environment=HALOGEN_MAX_TOK=65536
 # RAM left for the n-gram table the engine reads through the page cache.
 # Above the vendor's 20 because a dozen containers share this host; too low
 # and long prompts crawl with the disk busy.