Replaces the complete note event set of one note clip.
This is the ordinary, durable edit emitted by higher-level note transforms: the journal never records a callback invocation. The expected value makes replay conflict-aware, while swapping expected/replacement is the exact inverse used by undo.
The modifier arrays are optional. An authoring caller leaves both empty and the reducer carries the clip's existing modifiers across, dropping only the ones whose note the replacement removes. A reducer-built inverse fills them in, because the modifiers of a removed note are exactly what the note array alone cannot say: replacement_modifiers is the complete set to install and expected_modifiers is the set the clip must currently carry, gating the modifiers the same way the note arrays gate the notes.