Title: Kernel Gateway sends `input_request` with inconsistent session ID, causing kernel to hang on input()

[shakhbanov]

I am encountering a persistent issue where the Jupyter Kernel Gateway appears to send input_request messages with a session ID that is different from the session ID used in the initial execute_request. This inconsistency prevents the client from correctly replying to the input prompt, leading the kernel to hang in a "busy" state indefinitely.

Steps to Reproduce:

1. Client Setup: A web-based IDE (HTML/JavaScript) establishes a WebSocket connection to Jupyter Kernel Gateway.
   • The client successfully creates a new kernel via POST /api/kernels and receives a kernelId (e.g., 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e).
   • The client connects to the kernel's channels WebSocket using this kernelId.
2. Code Execution: The client sends an execute_request message with its header.session set to the established kernelId (e.g., 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e).
   • Example Code Executed:

     print("Part 1: This output works.")
     my_input = input("Enter something: ")
     print(f"Part 2: You entered: {my_input}")
     2 + 2

3. Inconsistent input_request (Server-side issue):
   • The Kernel Gateway processes the execute_request associated with session: 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e.
   • However, when the input() function is encountered, the Kernel Gateway sends an input_request message (and other subsequent messages like status, stream) to the client with a DIFFERENT header.session ID (e.g., c06b037c-7f03eeb634ab6e033f8bb7d0).
4. Client Reply Attempt:
   • The client correctly receives this input_request and stores its header as parent_header.
   • To reply, the client crafts an input_reply message:
     • header.session is forced to be the client's original kernelId (e.g., 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e) in an attempt to work around the inconsistency.
     • parent_header is set to the header of the received input_request (thus, parent_header.session is c06b037c-7f03eeb634ab6e033f8bb7d0).
5. Kernel Hangs: Despite the input_reply being sent, the kernel remains in a busy state, and the execution does not proceed past the input() call. This indicates that Kernel Gateway is not correctly associating the input_reply with the pending input_request.

Expected Behavior:

The session ID in messages sent by Kernel Gateway (e.g., input_request, status, stream) should consistently match the session ID of the execute_request that initiated the execution, or the kernelId of the WebSocket connection. The input_reply should then be processed correctly, allowing the kernel execution to complete.

Observed Behavior (with relevant log snippets):

Kernel Gateway Logs:

[19:08:06] [KernelGatewayApp] WARNING: No channel specified, assuming shell: {'header': {'msg_id': '0c3f0539-b9f4-4bf4-92f2-93d94e162abd', 'session': '8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e', 'date': '2025-07-31T19:08:06.673Z', 'msg_type': 'execute_request', 'version': '5.3'}, 'parent_header': {}, 'metadata': {}, 'content': {'code': 'print("Part 1: This output works.")\nmy_input = input("Enter something: ")\nprint(f"Part 2: You entered: {my_input}")\n2 + 2', 'silent': False, 'store_history': True, 'user_expressions': {}, 'allow_stdin': True, 'stop_on_error': True}, 'buffers': []}
[19:08:06] [KernelGatewayApp] DEBUG: activity on 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e: status (busy)
# ... (other messages from KG, e.g., stream, input_request, all with header.session: c06b037c-7f03eeb634ab6e033f8bb7d0) ...
[19:08:09] [KernelGatewayApp] WARNING: No channel specified, assuming shell: {'header': {'msg_id': '7d9b49dd-74bc-4c0d-a551-ab6f64b74d61', 'session': '8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e', 'date': '2025-07-31T19:08:09.388Z', 'msg_type': 'input_reply', 'version': '5.3'}, 'parent_header': {'msg_id': 'c06b037c-7f03eeb634ab6e033f8bb7d0_3367_13', 'msg_type': 'input_request', 'username': 'username', 'session': 'c06b037c-7f03eeb634ab6e033f8bb7d0', 'date': '2025-07-31T19:08:06.947924Z', 'version': '5.3'}, 'metadata': {}, 'content': {'value': 'Python', 'status': 'ok'}, 'buffers': []}

Client-side Browser Console Logs:

Ядро создано. Новый kernelId: 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e
python-4.html:796 Веб-сокет подключен к ядру: 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e
python-4.html:1052 Отправлено сообщение execute_request: 0c3f0539-b9f4-4bf4-92f2-93d94e162abd для session: 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e
python-4.html:803 [WS_MESSAGE] Type: status, Session: c06b037c-7f03eeb634ab6e033f8bb7d0, KernelId (client's): 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e
python-4.html:803 [WS_MESSAGE] Type: input_request, Session: c06b037c-7f03eeb634ab6e033f8bb7d0, KernelId (client's): 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e
python-4.html:904 Получен input_request. currentParentHeader установлен: {msg_id: 'c06b037c-7f03eeb634ab6e033f8bb7d0_3367_13', msg_type: 'input_request', username: 'username', session: 'c06b037c-7f03eeb634ab6e033f8bb7d0', date: '2025-07-31T19:08:06.947924Z', …}
python-4.html:733 Отправлено сообщение input_reply: 7d9b49dd-74bc-4c0d-a551-ab6f64b74d61 для session (принудительно): 8ccfcfaa-fb1e-4690-a7ac-2a6e5a17ea9e

Environment:

• Jupyter Kernel Gateway Version: (Please specify your Kernel Gateway version, e.g., output of jupyter kernelgateway --version)
• Client: Custom HTML/JavaScript based IDE using WebSocket for Jupyter Protocol communication.
• Operating System: (e.g., Linux, Windows, macOS)
• Python Version: (e.g., Python 3.9)

Additional Context:

This issue makes interactive input (input()) unusable with Jupyter Kernel Gateway, as the kernel consistently gets stuck. The client-side code has been modified to attempt to force the header.session of the input_reply to match the client's kernelId, but this workaround is ineffective due to the server's internal session ID mismatch.

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