Stub. The Probe layer reads ROOT TTrees in parallel and delivers typed payloads to user callbacks. Two payload shapes:

• Event — multi-row join across particle trees sharing an event-index branch (e.g. protons + pions for the same event).
• Feed — scalar per-entry payload from a single TTree (one Lorentz per labelled particle, plus named scalar/array node columns).

Streaming methods

Three entry points on ProbeParallel: streamEvents, streamFeed, stream.