diff --git a/src/boxes/map_box.rs b/src/boxes/map_box.rs
index be2bcc28..23d1c637 100644
--- a/src/boxes/map_box.rs
+++ b/src/boxes/map_box.rs
@@ -154,7 +154,7 @@ impl MapBox {
                 }
                 value.clone_box()
             }
-            None => Box::new(StringBox::new(&format!("Key not found: {}", key_str))),
+            None => Box::new(StringBox::new(&format!("[map/missing] Key not found: {}", key_str))),
         }
     }
 
diff --git a/tools/smokes/v2/lib/stageb_helpers.sh b/tools/smokes/v2/lib/stageb_helpers.sh
index 57bf56f4..078029c6 100644
--- a/tools/smokes/v2/lib/stageb_helpers.sh
+++ b/tools/smokes/v2/lib/stageb_helpers.sh
@@ -28,8 +28,8 @@ stageb_compile_to_json() {
       "$NYASH_BIN" --backend vm \
         "$NYASH_ROOT/lang/src/compiler/entry/compiler_stageb.hako" -- --source "$(cat "$hako_tmp")"
   ) > "$raw" 2>&1 || true
-  # Accept both MIR JSON v0 ("version":0, "kind":"Program") and Stage-1 JSON ("type":"Program")
-  if awk '(/"version":0/ && /"kind":"Program"/) || /"type":"Program"/ {print; found=1; exit} END{exit(found?0:1)}' "$raw" > "$json_out"; then
+  # Require MIR JSON v0 header: {"version":0, "kind":"Program", ...}
+  if awk '(/"version":0/ && /"kind":"Program"/) {print; found=1; exit} END{exit(found?0:1)}' "$raw" > "$json_out"; then
     rm -f "$raw" "$hako_tmp"
     echo "$json_out"
     return 0
diff --git a/tools/smokes/v2/profiles/quick/core/bridge/canonicalize_array_len_on_off_vm.sh b/tools/smokes/v2/profiles/quick/core/bridge/canonicalize_array_len_on_off_vm.sh
new file mode 100644
index 00000000..b6b8a843
--- /dev/null
+++ b/tools/smokes/v2/profiles/quick/core/bridge/canonicalize_array_len_on_off_vm.sh
@@ -0,0 +1,44 @@
+#!/bin/bash
+# canonicalize_array_len_on_off_vm.sh — Verify ArrayBox.len ModuleFunction → Method rewrite
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+if ROOT_GIT=$(git -C "$SCRIPT_DIR" rev-parse --show-toplevel 2>/dev/null); then
+  ROOT="$ROOT_GIT"
+else
+  ROOT="$(cd "$SCRIPT_DIR/../../../../../../../../.." && pwd)"
+fi
+source "$ROOT/tools/smokes/v2/lib/test_runner.sh"
+require_env || exit 2
+
+json_path="/tmp/ny_v1_array_len_$$.json"
+mut_on="/tmp/ny_v1_array_len_on_$$.json"
+mut_off="/tmp/ny_v1_array_len_off_$$.json"
+
+cat >"$json_path" <<'JSON'
+{"schema_version":"1.0","functions":[{"name":"main","blocks":[{"id":0,"instructions":[{"op":"const","dst":1,"value":{"type":"i64","value":0}},{"op":"mir_call","mir_call":{"callee":{"type":"ModuleFunction","name":"ArrayBox.len"},"args":[1]}},{"op":"ret"}]}]}]}
+JSON
+
+# ON → should rewrite to Method(box=ArrayBox, method=size, receiver=1)
+set +e
+HAKO_NYVM_V1_DOWNCONVERT=1 HAKO_BRIDGE_INJECT_SINGLETON=1 HAKO_DEBUG_NYVM_BRIDGE_DUMP_MUT="$mut_on" \
+  "$ROOT/target/release/nyash" --json-file "$json_path" >/dev/null 2>&1
+set -e || true
+if [ ! -f "$mut_on" ] || ! grep -q '"type":"Method"' "$mut_on" || ! grep -q '"box_name":"ArrayBox"' "$mut_on" || ! grep -q '"method":"size"' "$mut_on"; then
+  echo "[FAIL] canonicalize_array_len_on_off_vm (ON)" >&2; exit 1
+fi
+
+# OFF → should keep ModuleFunction (or no mutation dump)
+set +e
+HAKO_NYVM_V1_DOWNCONVERT=1 HAKO_DEBUG_NYVM_BRIDGE_DUMP_MUT="$mut_off" \
+  "$ROOT/target/release/nyash" --json-file "$json_path" >/dev/null 2>&1
+set -e || true
+if [ -f "$mut_off" ] && ! grep -q '"type":"ModuleFunction"' "$mut_off"; then
+  echo "[FAIL] canonicalize_array_len_on_off_vm (OFF)" >&2; exit 1
+fi
+
+echo "[PASS] canonicalize_array_len_on_off_vm"
+rm -f "$json_path" "$mut_on" "$mut_off"
+exit 0
+
diff --git a/tools/smokes/v2/profiles/quick/core/bridge/canonicalize_map_len_on_off_vm.sh b/tools/smokes/v2/profiles/quick/core/bridge/canonicalize_map_len_on_off_vm.sh
new file mode 100644
index 00000000..15c2f39c
--- /dev/null
+++ b/tools/smokes/v2/profiles/quick/core/bridge/canonicalize_map_len_on_off_vm.sh
@@ -0,0 +1,44 @@
+#!/bin/bash
+# canonicalize_map_len_on_off_vm.sh — Verify MapBox.len ModuleFunction → Method rewrite
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+if ROOT_GIT=$(git -C "$SCRIPT_DIR" rev-parse --show-toplevel 2>/dev/null); then
+  ROOT="$ROOT_GIT"
+else
+  ROOT="$(cd "$SCRIPT_DIR/../../../../../../../../.." && pwd)"
+fi
+source "$ROOT/tools/smokes/v2/lib/test_runner.sh"
+require_env || exit 2
+
+json_path="/tmp/ny_v1_map_len_$$.json"
+mut_on="/tmp/ny_v1_map_len_on_$$.json"
+mut_off="/tmp/ny_v1_map_len_off_$$.json"
+
+cat >"$json_path" <<'JSON'
+{"schema_version":"1.0","functions":[{"name":"main","blocks":[{"id":0,"instructions":[{"op":"const","dst":1,"value":{"type":"i64","value":0}},{"op":"mir_call","mir_call":{"callee":{"type":"ModuleFunction","name":"MapBox.len"},"args":[1]}},{"op":"ret"}]}]}]}
+JSON
+
+# ON → should rewrite to Method(box=MapBox, method=len, receiver=1)
+set +e
+HAKO_NYVM_V1_DOWNCONVERT=1 HAKO_BRIDGE_INJECT_SINGLETON=1 HAKO_DEBUG_NYVM_BRIDGE_DUMP_MUT="$mut_on" \
+  "$ROOT/target/release/nyash" --json-file "$json_path" >/dev/null 2>&1
+set -e || true
+if [ ! -f "$mut_on" ] || ! grep -q '"type":"Method"' "$mut_on" || ! grep -q '"box_name":"MapBox"' "$mut_on" || ! grep -q '"method":"len"' "$mut_on"; then
+  echo "[FAIL] canonicalize_map_len_on_off_vm (ON)" >&2; exit 1
+fi
+
+# OFF → should keep ModuleFunction (or no mutation dump)
+set +e
+HAKO_NYVM_V1_DOWNCONVERT=1 HAKO_DEBUG_NYVM_BRIDGE_DUMP_MUT="$mut_off" \
+  "$ROOT/target/release/nyash" --json-file "$json_path" >/dev/null 2>&1
+set -e || true
+if [ -f "$mut_off" ] && ! grep -q '"type":"ModuleFunction"' "$mut_off"; then
+  echo "[FAIL] canonicalize_map_len_on_off_vm (OFF)" >&2; exit 1
+fi
+
+echo "[PASS] canonicalize_map_len_on_off_vm"
+rm -f "$json_path" "$mut_on" "$mut_off"
+exit 0
+