feat: add multi-engine regex flavour support

engines/python/bridge.py

@@ -5,6 +5,7 @@ Pyodide runtime starts. User-controlled values are passed as function
 arguments; they are never evaluated as Python source.
 """
 
+import base64
 import json
 import re
 import sys
@@ -256,9 +257,16 @@ def _regex_tools_run(
             "resultsTruncated": results_truncated,
         }
         if operation == "replace":
+            output = "".join(output_chunks).encode("utf-8")
+            if len(output) != output_bytes:
+                return _error(
+                    "bridge",
+                    "output-byte-count-mismatch",
+                    "The bounded Python output byte count is inconsistent.",
+                )
             result.update(
                 {
-                    "output": "".join(output_chunks),
+                    "outputBase64": base64.b64encode(output).decode("ascii"),
                     "outputBytes": output_bytes,
                     "outputTruncated": output_truncated,
                 }