Implement stdin input_request test

[rgbkrk]

Summary

Implements the previously-stubbed stdin test to validate that kernels properly handle input requests during execution.

Changes:

• Add execute_with_stdin() helper to harness that:
  • Sets allow_stdin=true in execute request
  • Polls both IOPub and stdin channels concurrently
  • Responds to input_request with mock input_reply
• Implement test_stdin_input_request to verify:
  • Kernel sends input_request when code needs input
  • Execution completes successfully after receiving input

Results:

• ipykernel: 4/5 Tier 4 tests passing (was 3/5)
• Only comms_lifecycle remains as a stub

Test plan

• Verify ipykernel stdin test passes
• Check deno/evcxr behavior (may not support stdin)
• Confirm no regressions in other tests

[github-actions]

Kernel Conformance Matrix

Kernel	Tier 1	Tier 2	Tier 3	Tier 4	Total
deno	8/9	6/7	1/2	2/5	17/23
evcxr	9/9	3/7	1/2	2/5	15/23
ipykernel	9/9	7/7	2/2	4/5	22/23

---

deno (Deno kernel) - 3 failures, 3 skipped

Language: typescript | Protocol: 5.3

Failures

Test	Message Type	Likely Source	Reason
interrupt_request	interrupt_request	unknown	Timeout waiting for control reply
shutdown_reply	shutdown_request	unknown	Timeout waiting for control reply

Skipped (Not Implemented)

• display_data: Kernel can produce display_data messages for rich output
• stdin_input_request: Kernel can request input from frontend via stdin channel
• comms_lifecycle: Kernel supports comm open/msg/close lifecycle

evcxr (evcxr_jupyter) - 5 failures, 3 skipped

Language: Rust | Protocol: 5.3

Failures

Test	Message Type	Likely Source	Reason
inspect_request	inspect_request	unknown	Timeout waiting for shell reply
history_request	history_request	unknown	Timeout waiting for shell reply
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply
interrupt_request	interrupt_request	unknown	Protocol error: Error deserializing content for msg_type interrupt_reply: missing field status

Skipped (Not Implemented)

• display_data: Kernel can produce display_data messages for rich output
• stdin_input_request: Kernel can request input from frontend via stdin channel
• comms_lifecycle: Kernel supports comm open/msg/close lifecycle

ipykernel (ipython) - 0 failures, 1 skipped

Language: python | Protocol: 5.3

Skipped (Not Implemented)

• comms_lifecycle: Kernel supports comm open/msg/close lifecycle

---

Test Results by Message Type

Test	Message Type	deno	evcxr	ipykernel
comm_info_request	comm_info_request	✅	❌	✅
comms_lifecycle	comm_open	⏭️	⏭️	⏭️
complete_request	complete_request	✅	✅	✅
display_data	display_data	⏭️	⏭️	✅
error_handling	execute_request	✅	✅	✅
execute_input_broadcast	execute_input	✅	✅	✅
execute_reply_ok	execute_request	✅	✅	✅
execute_result	execute_result	✅	✅	✅
execute_stdout	execute_request	✅	✅	✅
execution_count_increments	execute_request	✅	✅	✅
heartbeat_responds	heartbeat	✅	✅	✅
history_request	history_request	✅	❌	✅
inspect_request	inspect_request	✅	❌	✅
interrupt_request	interrupt_request	❌	❌	✅
is_complete_complete	is_complete_request	✅	✅	✅
is_complete_incomplete	is_complete_request	⚠️	⚠️	✅
kernel_info_has_language_info	kernel_info_request	✅	✅	✅
kernel_info_has_protocol_version	kernel_info_request	✅	✅	✅
kernel_info_reply_valid	kernel_info_request	✅	✅	✅
parent_header_correlation	parent_header	✅	✅	✅
shutdown_reply	shutdown_request	❌	✅	✅
status_busy_idle_lifecycle	status	✅	✅	✅
stdin_input_request	input_request	⏭️	⏭️	✅