feat(frank-dragoon): double the KV pool to 2 x ctx for slot parity

frank-dragoon's total in-flight context was HALF frank-zealot's: zealot runs
one 401,408-position pool split into two 200,704 conversations, while dragoon
ran ONE 200,704-position pool behind its two slots, so a single maximum-length
request filled it and two long conversations had to stay under ~100k each.

HALOGEN_KV_POOL_POSITIONS 200704 -> 401408 = slots x ctx, the top of the seam's
legal band (ctx <= pool <= slots * ctx). The PER-REQUEST ceiling does not move:
HALOGEN_CTX stays 200704, because the checkpoint's native window is 262,144 and
the engine's own 400 text refuses to exceed it without HALOGEN_ROPE_YARN. What
this buys is concurrency, not a longer conversation, which is why the harness
contextWindow (155648 = ceiling - 45056) is untouched.

Cost: ~10.8 GiB of KV where 200,704 cost 5.5 (262,144 cost 7.2; the
2026-10-06 shape's 524,288 measured 14.6), taken from the page cache the 51.2 GB
n-gram table reads through — the warm prompt-cache ratio is the number to
re-measure after the boot. Engine-side total goes 74.1 -> ~79.4 GiB of 121.2.

Also carries scripts/download-frank-zealot-bonsai2-ptq1.sh: the PTQ1_0 candidate
payload fetcher (5,946,648,928 B, LFS sha256-verified, mmproj hardlinked), with
the publisher's own throughput table in its header — the packing is smaller but
the card measures it SLOWER on Ampere, so the swap is decided on our card, not
on the card's A100 row.

tests/frank_dragoon_unit.bats

@@ -82,7 +82,7 @@ good_env() {
         "FRANK_DRAGOON_TOKENIZER_FILES=tok.json"
         "HALOGEN_MODEL_ID=frank-dragoon"
         "HALOGEN_CTX=200704"
-        "HALOGEN_KV_POOL_POSITIONS=200704"
+        "HALOGEN_KV_POOL_POSITIONS=401408"
         "HALOGEN_KV_SLOTS=2"
         "HALOGEN_SPEC_ADAPT=0"
         "HALOGEN_MAX_TOK=8192"
@@ -155,11 +155,13 @@ good_env() {
     reserve="$(sed -nE 's/^HALOGEN_HOST_RESERVE_GIB=([0-9]+)$/\1/p' "$ENV_FILE")"
     # The pool is ONE budget behind the slots (boot ledger form: "2 slots over
     # ONE <pool>-position KV pool, each request up to HALOGEN_CTX"), NOT
-    # slots x ctx — one window behind both slots IS the memory saving. What
-    # still binds: the pool must back ONE full-length request (or the
+    # a per-slot private pool. Since 2026-10-18 it is sized pool = slots * ctx
+    # (401,408 = 2 x 200,704), so two MAXIMUM-length conversations can be
+    # resident at once — frank-zealot parity on total in-flight context. What
+    # still binds: the pool must back ONE full-length request (below that the
     # advertised per-request ceiling would be unreachable, hence pool >= ctx),
-    # it must not pretend to be slots x ctx (pool <= slots * ctx), and the
-    # ledger sum below must stay inside unified memory.
+    # it must not pretend to be more than slots x ctx (pool <= slots * ctx), and
+    # the ledger sum below must stay inside unified memory.
     [ "$pool" -ge "$ctx" ]
     [ "$pool" -le $(( slots * ctx )) ]
     kv_gib=$(( pool * 28 * 1024 / 1073741824 ))
@@ -274,7 +276,7 @@ $(cat "$TEST_TMP/serve.log")"
     [[ "$output" == *"--publish 7770:8731"* ]]
     [[ "$output" == *"-e HALOGEN_MODEL_ID=frank-dragoon"* ]]
     [[ "$output" == *"-e HALOGEN_CTX=200704"* ]]
-    [[ "$output" == *"-e HALOGEN_KV_POOL_POSITIONS=200704"* ]]
+    [[ "$output" == *"-e HALOGEN_KV_POOL_POSITIONS=401408"* ]]
     [[ "$output" == *"-e HALOGEN_KV_SLOTS=2"* ]]
     [[ "$output" == *"-e HALOGEN_SPEC_ADAPT=0"* ]]
     [[ "$output" == *"-e HALOGEN_CHECKPOINT=/models/qwen.hgn"* ]]