perf(scene): stop re-tessellating on preview/interim overlay updates

Phase 2.2 (partial). set_preview_wires / clear_preview_wire /
set_interim_wire called bump_geometry, so every rubber-band frame of a
drawing command invalidated the wire cache and re-tessellated the whole
model — the same 30ms->400ms spike as selection, but while drawing.

Preview / interim wires are an overlay appended to the cached base wire
set in build_primitive; they are not part of the tessellation cache, so
they no longer bump geometry. The base model-tile tessellation stays a
cache hit (static camera, no geometry bump), and the overlay still forces
a GPU wire re-upload through the has_overlay content-id path. Real commits
(commit_entity / transform / copy) bump geometry on their own, so finished
edits and preview-clear still render correctly. Snap/hit-test via
entity_wires_arc also stops re-tessellating per preview frame.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

ROADMAP.md

@@ -132,6 +132,16 @@ handles; the render path re-tessellates only those, reusing the rest.
 Also useful on open: any partial cache (e.g. from block defns) can be
 re-used.
 
+**Partial (landed): preview / interim overlays.** `set_preview_wires`,
+`clear_preview_wire` and `set_interim_wire` used to `bump_geometry`, so every
+rubber-band frame of a drawing command re-tessellated the whole model (the
+same 30 ms → 400 ms spike, but while drawing). Preview / interim wires are an
+overlay appended to the cached base wire set in `build_primitive`, not part of
+the tessellation cache — so they no longer bump geometry. The base stays a
+cache hit (no re-tess), and the overlay forces only a GPU wire re-upload via
+the `has_overlay` content-id path. Snap/hit-test (`entity_wires_arc`) also
+stops re-tessellating per preview frame.
+
 ### 2.3 Progressive first render
 
 On the first frame emit a **coarse**-tol wire pass (e.g. 4× the normal

src/scene/mod.rs

@@ -4251,14 +4251,21 @@ impl Scene {
     // ── Preview wire ──────────────────────────────────────────────────────
 
     pub fn set_preview_wires(&mut self, wires: Vec<WireModel>) {
+        // Preview wires are an overlay appended to the cached base wire set in
+        // `build_primitive`; they are NOT part of the tessellation cache. So a
+        // preview update must NOT bump `geometry_epoch` — that would re-
+        // tessellate the whole model on every rubber-band frame. The overlay
+        // forces a GPU wire re-upload on its own (the `has_overlay` content-id
+        // path), and iced redraws after the message that set the preview.
         self.preview_wires = wires;
-        self.bump_geometry();
     }
 
     pub fn clear_preview_wire(&mut self) {
+        // No geometry bump — see `set_preview_wires`. Dropping the overlay
+        // flips the wire content id back to the base tessellation id, which
+        // re-uploads the base wires (without the preview) on the next frame.
         self.preview_wires = vec![];
         self.interim_wire = None;
-        self.bump_geometry();
     }
 
     pub fn wire_models_for(&self, handles: &[acadrust::Handle]) -> Vec<WireModel> {
@@ -4284,8 +4291,9 @@ impl Scene {
     }
 
     pub fn set_interim_wire(&mut self, w: WireModel) {
+        // Overlay wire — same reasoning as `set_preview_wires`: no geometry
+        // bump, so the model isn't re-tessellated on every interim update.
         self.interim_wire = Some(w);
-        self.bump_geometry();
     }
 
     // ── Selection ─────────────────────────────────────────────────────────