Module evidence before editing / concept
Evidence before editing: working system
Create an evidence-backed fault boundary before changing configuration or code.
18 minutesSystem model
Working systemEvidence boundaryExpected output
Minimum concept
A symptom describes what an operator can observe. A cause explains why the system produced that symptom. Treating those as the same thing leads to random edits.
Start at the system boundary, verify process health, then move inward through nodes, interfaces, messages, and timing. Record each observation before forming a hypothesis.
Working example
A healthy delivery stack shows one process, three ROS nodes, expected graph edges, and a heartbeat that advances every second.
$ ps -ef$ ros2 node list$ ros2 doctor --reportCheck understanding