Evidence
A count you can't audit is a rumor with a number on it. Every event Praxis emits carries enough attached material to reconstruct exactly why it fired.
Operational users don't act on model output. They act on model output they can defend afterwards, to a supervisor, in a report, sometimes in court. So evidence in Praxis is not a logging feature bolted on at the end; it's part of the event itself, generated at the moment the rule fires.
What attaches to an event#
| Artifact | Contents |
|---|---|
crop | Frame crop of the object at fire time, with the detection box |
track_history | The object's full position history from first sighting to the event |
zone_geometry | The zone polygon as registered on that exact frame |
context | Feed ID, frame index, timestamp, rule and runtime versions |
The zone geometry entry deserves a note. Because zones are world-anchored, the polygon differs slightly on every frame. The evidence records the geometry the rule actually evaluated, so an entry can be re-checked later without rerunning the whole pipeline.
Replay as proof#
The purest form of evidence is watching the system work. The challengereplay is built on this idea: after you count manually, it plays the clip back with every detection boxed, every counted car flagged in red at the moment it entered, and a running log of timestamped entries. Nothing in that replay is rendered specially for the demo. It's the event stream and its evidence, drawn on the footage.