MorphPieceChannel class

A per-frame geometry channel for a MorphPiece: a translation plus per-axis scales over the piece's base MorphPiece.rect, written by the app (a drag, a tether, an orbit) and consumed by the skin's render object directly. A write repaints and re-traces the skin with no widget rebuild and no relayout - the same citizenship flight ticks have.

The delta lives in the group's local pixels and applies about the base rect's center. The skin mirrors it onto the piece's mass and, as a child-local paint transform, onto the content: one rigid body. The content paint-scales rather than reflows (text does not rewrap at a stretched width) - the contract of the channel, invisible at tether scales. A MorphTag inside the content measures itself through the same transform, so a flight launches from wherever the piece currently stands; hit testing follows the displaced content, which must stay within the group's own box to remain reachable.

The app owns the channel: create it in a State, dispose it there, hand it to MorphPiece.channel. Transient motion (a drag) commits into the base rect at rest and calls reset - the channel carries the live delta, the rect carries the truth.