langchain-ai/langgraph · error · DuplicateHandlerError

Blob decryptor already registered

Error message

Blob decryptor already registered

What it means

Raised (as DuplicateHandlerError) by the encryption context's register decorator when a blob decryptor has already been registered for the context. Only one decryptor per registration slot is allowed; a second registration is rejected to avoid ambiguous decryption behavior. Register the decryptor once.

Solutions

1. Remove the extra @encryption.decrypt.blob registration so only one blob decryptor exists
2. Route different decryption paths through the single handler based on ctx

When it happens

Trigger: Thrown at libs/sdk-py/langgraph_sdk/encryption/__init__.py:173 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/4ca3b0f6789588c1. Report an issue: GitHub.

Appendix: source

Thrown at libs/sdk-py/langgraph_sdk/encryption/__init__.py:173

            async def decrypt_blob(
                ctx: EncryptionContext, blob: bytes
            ) -> bytes | DecryptResult[bytes]:
                # Decrypt the blob using your encryption service
                return decrypted_blob
            ```

        Args:
            fn: The decryption handler function

        Returns:
            The registered handler function

        Raises:
            DuplicateHandlerError: If blob decryptor already registered
            TypeError: If handler has invalid signature
        """
        if self._parent._blob_decryptor is not None:
            raise DuplicateHandlerError("Blob decryptor already registered")
        _validate_handler(fn, "Blob decryptor")
        self._parent._blob_decryptor = fn
        return fn

    def json(self, fn: _JsonDecryptorT) -> _JsonDecryptorT:
        """Register the JSON decryption handler.

        Example:
            ```python
            @encryption.decrypt.json
            async def decrypt_json(
                ctx: EncryptionContext, data: dict
            ) -> dict | DecryptResult[dict]:
                # Decrypt the data
                return decrypt_data(data)
            ```

        Args:

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