Reduce frank-default-large context for KV headroom

tests/frank_large_config.bats

@@ -39,6 +39,11 @@ TEMPLATE_FILE="$REPO_ROOT/scripts/chat-template.jinja"
     grep -q '^MTP_BACKEND_SAMPLING=on$' "$ENV_FILE"
 }
 
+@test "frank-default-large fits the model and KV cache in unified memory" {
+    grep -q '^CTX_SIZE=196608$' "$ENV_FILE"
+    grep -q ': "${CTX_SIZE:=262144}"' "$SERVE_FILE"
+}
+
 @test "frank-default-large exposes a swappable ubatch" {
     grep -q '^UBATCH_SIZE=256$' "$ENV_FILE"
     grep -q ': "${UBATCH_SIZE:=256}"' "$SERVE_FILE"