Merged FN-4244: adds an override path for the no-task heartbeat procedure in the engine, allowing agents to execute a custom procedure when they have no active task. The fix commit corrects the initial implementation, with test coverage for procedure source selection and updated documentation in `do
Fusion-Task-Id: FN-4244
Fusion-Task-Lineage: 6bf1bfe4-de2c-4467-93dc-d90231a53eb2