runner: introduce CoreExecutor box for JSON→exec; wire Gate‑C pipe to CoreExecutor. Stage‑B bundling: duplicate name Fail‑Fast + mix canary; add Core Map/String positive smokes; add Gate‑C budget opt‑in canary; docs: Exit Code Policy; apply child_env in PyVM common util.

src/runner/core_executor.rs

@@ -0,0 +1,65 @@
+/*!
+ * CoreExecutor — JSON v0 → Execute (boxed)
+ *
+ * Responsibility
+ * - Single entry to execute a MIR(JSON) payload under Gate‑C/Core policy.
+ * - Encapsulates: optional canonicalize, v1-bridge try, v0-parse fallback,
+ *   OOB strict observation, and rc mapping via MIR Interpreter.
+ *
+ * Notes
+ * - For now, execution uses the existing MIR Interpreter runner
+ *   (execute_mir_module_quiet_exit). Later we can swap internals to call
+ *   the Core Dispatcher directly without touching callers.
+ */
+
+use super::NyashRunner;
+
+pub(crate) fn run_json_v0(runner: &NyashRunner, json: &str) -> i32 {
+    let mut payload = json.to_string();
+
+    let use_core_wrapper = crate::config::env::nyvm_core_wrapper();
+    let use_downconvert = crate::config::env::nyvm_v1_downconvert();
+
+    if use_core_wrapper || use_downconvert {
+        // Best-effort canonicalize
+        if let Ok(j) = crate::runner::modes::common_util::core_bridge::canonicalize_module_json(&payload) {
+            payload = j;
+        }
+        match crate::runner::json_v1_bridge::try_parse_v1_to_module(&payload) {
+            Ok(Some(module)) => {
+                super::json_v0_bridge::maybe_dump_mir(&module);
+                // OOB strict: reset observation flag
+                crate::runner::child_env::pre_run_reset_oob_if_strict();
+                let rc = runner.execute_mir_module_quiet_exit(&module);
+                if crate::config::env::oob_strict_fail() && crate::runtime::observe::oob_seen() {
+                    eprintln!("[gate-c][oob-strict] Out-of-bounds observed → exit(1)");
+                    return 1;
+                }
+                return rc;
+            }
+            Ok(None) => { /* fall through to v0 */ }
+            Err(e) => {
+                eprintln!("❌ JSON v1 bridge error: {}", e);
+                return 1;
+            }
+        }
+    }
+
+    match super::json_v0_bridge::parse_json_v0_to_module(&payload) {
+        Ok(module) => {
+            super::json_v0_bridge::maybe_dump_mir(&module);
+            crate::runner::child_env::pre_run_reset_oob_if_strict();
+            let rc = runner.execute_mir_module_quiet_exit(&module);
+            if crate::config::env::oob_strict_fail() && crate::runtime::observe::oob_seen() {
+                eprintln!("[gate-c][oob-strict] Out-of-bounds observed → exit(1)");
+                return 1;
+            }
+            rc
+        }
+        Err(e) => {
+            eprintln!("❌ JSON v0 bridge error: {}", e);
+            1
+        }
+    }
+}
+