Gate‑C(Core) OOB strict fail‑fast; String VM handler normalization; JSON lint Stage‑B root fixes via scanner field boxing and BinOp operand slotify; docs + smokes update

src/config/env.rs

@@ -554,3 +554,12 @@ pub fn nyvm_v1_downconvert() -> bool {
         .or_else(|| env_flag("NYASH_NYVM_V1_DOWNCONVERT"))
         .unwrap_or(false)
 }
+
+/// Gate‑C(Core) strict OOB handling: when enabled, any observed OOB tag
+/// (emitted by runtime during ArrayBox get/set with HAKO_OOB_STRICT=1) should
+/// cause non‑zero exit at the end of JSON→VM execution.
+pub fn oob_strict_fail() -> bool {
+    env_flag("HAKO_OOB_STRICT_FAIL")
+        .or_else(|| env_flag("NYASH_OOB_STRICT_FAIL"))
+        .unwrap_or(false)
+}