github/copilot-sdk · error · RuntimeError

User input requested but no handler registered

Error message

User input requested but no handler registered

What it means

Raised by CopilotSession's user-input request dispatcher in python/copilot/session.py when the host sends a user-input request but no user-input handler was registered on the session (self._user_input_handler is None). The SDK cannot prompt the user, so it fails the request immediately with a RuntimeError.

Solutions

1. Register a user-input handler on the session (the callback receiving UserInputRequest) before sending any prompt.
2. Re-register the handler after resume_session — registrations are per-session and not persisted.
3. If prompting is impossible in your environment, configure the session/agent to run without user questions (e.g. non-interactive mode) so no user-input request is issued.
4. Inspect the request's question field in your handler and return a structured response dict; wrap handler code in try/except so handler bugs don't masquerade as missing-handler errors.

Example fix

# before
session = await client.create_session()
await session.send_and_wait("Deploy to prod?")  # RuntimeError: no user-input handler

# after
session = await client.create_session()
session.register_user_input_handler(lambda req: {"answer": input(req.question)})
await session.send_and_wait("Deploy to prod?")

if getattr(session, "_user_input_handler", None) is None:
    raise ValueError("register a user-input handler before sending prompts that may ask questions")

def has_user_input_handler(session) -> bool:
    return callable(getattr(session, "_user_input_handler", None))

try:
    message = await session.send_and_wait(prompt)
except RuntimeError as e:
    if "no handler registered" in str(e):
        session.register_user_input_handler(default_console_handler)
        message = await session.send_and_wait(prompt)
    else:
        raise

When it happens

Trigger: The agent issues a user-input request during a turn while the application never called the session's register/set user-input handler (or explicitly cleared it by passing None).

Common situations: Headless/embedded integrations that don't wire a user-input callback; registering handlers after the first prompt already triggered a request; accidentally passing None to clear handlers while the agent still asks questions.

Understand the failure class

Background: "X is required", "must be set", "cannot be empty": the missing-required-config error family, from Vertex AI project/location to WeChat keys — this error's family across 18 libraries.

Related errors

• User input requested but no handler registered
• no user input handler registered
• No session found for sessionId
• Session not found
• canvas_action_no_handler

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/8a811b91d43092fb. Report an issue: GitHub.

Appendix: source

Thrown at python/copilot/session.py:2829

    async def _handle_user_input_request(self, request: dict) -> UserInputResponse:
        """
        Handle a user input request from the Copilot CLI.

        Note:
            This method is internal and should not be called directly.

        Args:
            request: The user input request data from the CLI.

        Returns:
            A dictionary containing the user's response.
        """
        with self._user_input_handler_lock:
            handler = self._user_input_handler

        if not handler:
            raise RuntimeError("User input requested but no handler registered")

        try:
            handler_start = time.perf_counter()
            result = handler(
                UserInputRequest(
                    question=request.get("question", ""),
                    choices=request.get("choices") or [],
                    allowFreeform=request.get("allowFreeform", True),
                ),
                {"session_id": self.session_id},
            )
            if inspect.isawaitable(result):
                result = await result
            log_timing(
                logger,
                logging.DEBUG,
                "CopilotSession._handle_user_input_request dispatch",
                handler_start,

View on GitHub (pinned to cd8cf15dc3)