Immutable controller/expression value lowered by the program compiler.
This is the runtime counterpart of timeline::MidiExpressionLane, and it deliberately mirrors NoteProgramEvent: the sample position is authoritative for half-open block scheduling against the exact CompiledTempoMap the owning PlaybackProgram was built with, while the tick stays available for diagnostics and state snapshots.
The full wire address is carried rather than a Pulp-local controller enumeration, so a controller family nobody anticipated needs new values and never a new type — the same reason the storage lane keeps the wire encoding. lane_id and point_id preserve authored provenance through flattening, so a value can still be traced back to the lane and the point that produced it after a nested sequence has been expanded. A chased value keeps the provenance of the point it read, which is what makes it reproducible.