refactor: cleanup duplicate code (#36173)

api/controllers/common/human_input.py

@@ -1,6 +1,21 @@
+import json
+
 from pydantic import BaseModel, JsonValue
 
 
 class HumanInputFormSubmitPayload(BaseModel):
     inputs: dict[str, JsonValue]
     action: str
+
+
+def stringify_form_default_values(values: dict[str, object]) -> dict[str, str]:
+    """Serialize default values into strings expected by human-input form clients."""
+    result: dict[str, str] = {}
+    for key, value in values.items():
+        if value is None:
+            result[key] = ""
+        elif isinstance(value, (dict, list)):
+            result[key] = json.dumps(value, ensure_ascii=False)
+        else:
+            result[key] = str(value)
+    return result