Function set_param 

pub fn set_param(
    tree: &PatchTree,
    addr: &str,
    value: ParamValue,
) -> Result<PatchTree, EditError>

Return a copy of tree with the choice at addr set to value.

Continuous values are clamped to [0, 1]; enum indices are clamped to the site’s arity. Structural sites are rejected — restructuring is evolution’s job (or a future explicit structure-edit surface), not a knob gesture.

Identity is carried across, because a knob turn changes no structure and therefore renames nothing. That has to be said explicitly: this edit is performed on the trace — a map from address to value — and PatchTree::from_trace rebuilds the term through the genome decoder, which has never heard of a crate::term::Uid and cannot. So every node comes back anonymous unless it is told otherwise, which is the same round trip (and the same fix) as the refinement path in record_child. Left alone it is not a cosmetic loss: every lock id collapses onto the same 0#site, a re-render looks to the motion system like the entire patch arriving at once, and every hand-placed position is orphaned — by turning one knob.