layouts: keep every content viewport's wires cached (#1769)

The resident wire sets were capped at 16 and cleared once more were
held. A layout with more content viewports than that (24 in the report)
cleared them all on each redraw and re-tessellated the model for every
viewport, so the layout stayed sluggish even when nothing changed. The
cap now covers the shown layout's viewports: idle redraws build no
wires, and a frame of that layout draws in ~14 ms instead of ~30 ms
plus ~100 ms of rebuilds.

The automation bridge gains a `layout_switch` action, as clicking a
layout tab does, which is how this was measured.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/control/actions.rs

@@ -1166,6 +1166,8 @@ impl OpenCADStudio {
         let name = string(req, "name")?;
         let msg = match name {
             "close_modal" => Message::CloseModal,
+            // Show a layout (or "Model"), as clicking its tab does.
+            "layout_switch" => Message::LayoutSwitch(string(req, "value")?.into()),
             // The "changed outside" modal's suggested actions (D6): reload
             // the disk copy, keep the in-memory one and overwrite, save as,
             // or dismiss. Native only — the web build has no such dialog.

src/scene/mod.rs

@@ -7223,12 +7223,20 @@ impl Scene {
         if block == self.model_space_block_handle() {
             *self.model_wire_gpu_patch.borrow_mut() = None;
         }
+        // Every content viewport of the shown layout holds a set of its own;
+        // a cap below their count cleared them all each frame and rebuilt
+        // every viewport's wires on every redraw (#1769).
+        let shown = if self.current_layout == "Model" {
+            0
+        } else {
+            self.paper_viewport_handles().2.len()
+        };
         let mut sets = self.resident_wire_sets.borrow_mut();
         // Evict stale entries (older epochs / abandoned keys) so switching
         // spaces or re-scaling a viewport can't accumulate dead full sets.
         let cur_epoch = self.geometry_epoch;
         sets.retain(|_, set| set.epoch == cur_epoch);
-        if sets.len() > 16 {
+        if sets.len() > 16.max(shown + 2) {
             sets.clear();
         }
         sets.insert(