fix(broker): cancel zombie coroutine and reset connection on execute timeout (#925)

[oboehmer]

Description

Cancels the underlying asyncio coroutine when future.result(timeout=DEVICE_EXECUTE_TIMEOUT) times out in SSHTestBase._patch_device_execute_for_broker(), and ensures BrokerClient tears down the socket connection on cancellation to prevent zombie coroutines from blocking subsequent broker commands or reusing a desynchronized socket stream.

Closes

• Fixes Cancel zombie coroutine on broker future.result() timeout (or serialize broker requests) #925

Related Issue(s)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring / Technical debt (internal improvements with no user-facing changes)
• Documentation update
• Chore (build process, CI, tooling, dependencies)
• Other (please describe):

Test Framework Affected

• PyATS
• Robot Framework
• Both
• N/A (not test-framework specific)

Network as Code (NaC) Architecture Affected

• ACI (APIC)
• NDO (Nexus Dashboard Orchestrator)
• NDFC / VXLAN-EVPN (Nexus Dashboard Fabric Controller)
• Catalyst SD-WAN (SDWAN Manager / vManage)
• Catalyst Center (DNA Center)
• ISE (Identity Services Engine)
• FMC (Firepower Management Center)
• Meraki (Cloud-managed)
• NX-OS (Nexus Direct-to-Device)
• IOS-XE (Direct-to-Device)
• IOS-XR (Direct-to-Device)
• Hyperfabric
• All architectures
• N/A (architecture-agnostic)

Platform Tested

nac-test supports macOS and Linux only

• macOS (version tested: Darwin 25.3.0 / macOS 15)
• Linux (distro/version tested: )

Key Changes

• In ssh_base_test.py: Catch TimeoutError on future.result(timeout=DEVICE_EXECUTE_TIMEOUT) and invoke future.cancel() to cancel the underlying task on the event loop.
• In broker_client.py: Catch asyncio.CancelledError in _send_request and call self._teardown_connection() so the cancelled in-flight socket stream is cleanly reset and cannot corrupt or stall the next command.
• In test_ssh_base_test.py: Added assertion that mock_future.cancel() is called on timeout.
• In test_connection_broker.py: Added TestBrokerClientCancellation verifying that a cancelled hanging request tears down the connection and enables subsequent commands on the client to reconnect and succeed without queueing or errors.

Testing Done

• Unit tests added/updated
• Integration tests performed
• Manual testing performed:
  • PyATS tests executed successfully
  • Robot Framework tests executed successfully
  • D2D/SSH tests executed successfully (if applicable)
  • HTML reports generated correctly
• All existing tests pass (pytest / pre-commit run -a)

Test Commands Used

pytest tests/unit/pyats_core/
pre-commit run -a

Checklist

• Code follows project style guidelines (pre-commit run -a passes)
• Self-review of code completed
• Code is commented where necessary (especially complex logic)
• Documentation updated (if applicable)
• No new warnings introduced
• Changes work on both macOS and Linux
• CHANGELOG.md updated (if applicable)

Screenshots (if applicable)

N/A

Additional Notes

None