frank-primary: 3 full windows, pool at the contract floor, MNBT 2048

Frank's call 2026-10-01: MAXLEN 262144 x SEQS 3 = 786,432 tokens of contract.
Measured fp8 KV costs 7,698 B/token (4-slot boot 8,311,013,376 B -> 1,079,582
tokens; 5-slot boot 10,388,766,720 B -> 1,350,182 tokens), so the pool floor
for the contract is 6.054e9 B. Pinned at 6,100,000,000 (~792k tokens, ~5.9k
margin) so the remaining ~2.2 GiB versus the 4-slot shape goes to the expert
ARENA - the fork sizes its decode-critical expert cache from the remainder
after weights, pool and workspace.

MNBT 2048 (Frank): the arena sweep measured 6,499 slots at every rung <= 4096,
so the larger batch costs the arena nothing.

Seam retargeted (3 seqs / 6.1e9 / MNBT 2048); docs + AGENTS row + log updated,
including the closed DCP investigation.

tests/frank_primary_unit.bats

@@ -89,12 +89,16 @@ DOWNLOAD="$REPO_ROOT/scripts/download-frank-primary.sh"
     # deployed shape: ~1.93 GiB more headroom per rank for
     # activations/graphs. UTIL stays 0.98 (lowering it shrinks the engine's
     # own budget instead of buying slack).
+    # 3 x 262144 = 786,432 tokens; at the measured 7,698 B/token the pool
+    # floor is 6.054e9 B, pinned at 6.1e9 so the margin is ~5.9k tokens and
+    # EVERYTHING ELSE goes to the expert arena (the decode-critical expert
+    # cache is the remainder after weights, pool and workspace).
     grep -q '^FRANK_PRIMARY_MAXLEN=262144$' "$ENV_FILE"
-    grep -q '^FRANK_PRIMARY_SEQS=4$' "$ENV_FILE"
+    grep -q '^FRANK_PRIMARY_SEQS=3$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_UTIL=0.98$' "$ENV_FILE"
-    grep -q '^FRANK_PRIMARY_KV_BYTES=8311013376$' "$ENV_FILE"
+    grep -q '^FRANK_PRIMARY_KV_BYTES=6100000000$' "$ENV_FILE"
+    grep -q '^FRANK_PRIMARY_MNBT=2048$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_KV_DTYPE=fp8$' "$ENV_FILE"
-    grep -q '^FRANK_PRIMARY_MNBT=1024$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_GATHER_CHUNKS=32$' "$ENV_FILE"
     grep -q '^FRANK_PRIMARY_GATHER_LANES=64$' "$ENV_FILE"
     ! grep -q '^FRANK_PRIMARY_SPEC=' "$ENV_FILE"
@@ -182,11 +186,13 @@ DOWNLOAD="$REPO_ROOT/scripts/download-frank-primary.sh"
     grep -q -- '-e R4D_LRU_GATHER_CHUNKS="$FRANK_PRIMARY_GATHER_CHUNKS"' "$SERVE"
 }
 
-@test "MNBT is locked at 1024" {
-    # Frank's lock: MNBT 512 doubles TTFT at 4064 ctx (2.46 s vs 1.36 s);
-    # 1024-4096 are interchangeable on decode; 12288 costs 2.5% plus arena.
-    # 1024 keeps the workspace floor so the expert arena stays max.
-    grep -q '^FRANK_PRIMARY_MNBT=1024$' "$ENV_FILE"
+@test "MNBT is at Frank's 2048 with the arena intact" {
+    # MNBT 512 doubles TTFT at 4064 ctx (2.46 s vs 1.36 s); 1024-4096 are
+    # interchangeable on decode AND identical on arena (the sweep measured
+    # 6,499 slots at every rung <=4096); 12288 costs 2.5% plus arena.
+    # 2048 is Frank's setting as of 2026-10-01 — it keeps the workspace floor
+    # so the expert arena stays max.
+    grep -q '^FRANK_PRIMARY_MNBT=2048$' "$ENV_FILE"
     grep -q -- '--max-num-batched-tokens "$FRANK_PRIMARY_MNBT"' "$SERVE"
 }