core: add Core Direct string canaries (substring/charAt/replace); Stage‑B: alias table (ENV) support with BundleResolver; docs: Exit Code Policy tag→rc rules and checklist updates.

src/runner/core_executor.rs

@@ -119,5 +119,5 @@ fn try_run_core_direct(json: &str) -> Option<i32> {
             break;
         }
     }
-    rc
+    if let Some(code) = rc { Some(code) } else { Some(1) }
 }