fix(wt-memory-gate-batch): pass --legacy-mode only when the deployed harness has it

b193 (U11b) retired the legacy plane and removed --legacy-mode from the
harness; passing it there fails the daily batch. The wrapper now greps
core/memory_acceptance at the deployed sha and omits the flag when it is
gone, so it is correct on both sides of the b192 -> b193 deploy (checked:
7a83f2f -> passes it, c2d87263 -> omits it).

scripts/wt-memory-gate-batch

@@ -41,8 +41,11 @@
 #   WT_DEMO_API_CT   default worldtree-worldtree-api-1
 #   WT_LEGACY_MODE   default off      (U11a ruling 2026-09-30: off, not read_only)
 #   WT_BATCH_LABEL   default window-off
-# Until the U11b retirement unit lands. After it, `off` is the only mode, the
-# harness drops --legacy-mode, and this script needs that flag removed.
+# WT_LEGACY_MODE is passed ONLY when the deployed sha's harness still has --legacy-mode.
+# b193 (U11b, 2026-10-02) retired the legacy plane and removed the flag; passing it there
+# fails the batch. The check greps core/memory_acceptance/ AT THE DEPLOYED SHA (the argparse
+# lives in live_driver.py; live.py only imports it), so
+# the wrapper is right on both sides of the b192 -> b193 deploy without a timed edit.
 set -euo pipefail
 
 WT_TREE="${WT_TREE:-$HOME/development/Worldtree}"
@@ -105,8 +108,12 @@ else
   where="detached worktree $WT_GATE_TREE (tree HEAD ${head:0:12} != deployed)"
 fi
 
+legacy_args=()
+if git -C "$WT_TREE" grep -q -e '"--legacy-mode"' "$deployed" -- core/memory_acceptance 2>/dev/null; then
+  legacy_args=(--legacy-mode "$WT_LEGACY_MODE")
+fi
 cmd=(python -m core.memory_acceptance.live --runs 3 --gate
-     --legacy-mode "$WT_LEGACY_MODE" --label "$WT_BATCH_LABEL" --out "$OUT_DIR")
+     "${legacy_args[@]}" --label "$WT_BATCH_LABEL" --out "$OUT_DIR")
 
 echo "wt-memory-gate-batch $(now)"
 echo "  demo image   $image"