perf(render): arena on by default; trim per-edit resident + text work

Three cuts to the per-edit cost, on top of the incremental wire arena:

- Enable OCS_WIRE_GPU_PATCH by default (kill-switch OCS_WIRE_GPU_PATCH=0), so the
  in-place / append-tombstone arena — validated on the reference drawing (wire
  block ~300ms + 265MB upload -> ~2ms) — is on for everyone; a bail always falls
  back to the identical batched path.

- Resident patch: an all-Modified edit never reorders, so reassemble by walking
  the recorded assembled order (~10k handles) instead of scanning the whole
  document (~800k) to re-derive draw order. Add/Remove still scan (positions
  change). ~14ms -> <1ms on a move.

- SDF text: a new content id misses the glyph cache every edit, but if no
  text-bearing entity (Text/MText/Dimension/MLeader/Leader/Table/attribute/INSERT)
  changed since the last build the glyphs are identical, so reuse them. ~23ms -> 0
  on a plain-geometry edit.

A move/edit on this 800k-entity drawing now spends ~50ms (dominated by the undo
document clone) instead of ~85ms, and the wire GPU upload is gone.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/view/render.rs

@@ -990,6 +990,25 @@ impl Scene {
                 return verts.clone();
             }
         }
+        // A new content id (every geometry edit) misses the cache — but if no
+        // text-bearing entity changed since the last build, the glyphs are
+        // identical, so reuse them instead of re-walking every wire.
+        {
+            let reuse = {
+                let last = self.last_sdf_text.borrow();
+                match &*last {
+                    Some((epoch, arc)) if self.text_unchanged(*epoch) => Some(arc.clone()),
+                    _ => None,
+                }
+            };
+            if let Some(arc) = reuse {
+                self.sdf_text_cache
+                    .borrow_mut()
+                    .insert(wire_content_id, arc.clone());
+                *self.last_sdf_text.borrow_mut() = Some((self.geometry_epoch, arc.clone()));
+                return arc;
+            }
+        }
         let mut out: Vec<crate::scene::pipeline::text_gpu::TextVertex> = Vec::new();
         for w in wires {
             if !w.text_verts.is_empty() {
@@ -997,12 +1016,15 @@ impl Scene {
             }
         }
         let verts = Arc::new(out);
-        let mut cache = self.sdf_text_cache.borrow_mut();
-        // Ids change on rebuild, so old keys die naturally; cap bounds churn.
-        if cache.len() > 8 {
-            cache.clear();
+        {
+            let mut cache = self.sdf_text_cache.borrow_mut();
+            // Ids change on rebuild, so old keys die naturally; cap bounds churn.
+            if cache.len() > 8 {
+                cache.clear();
+            }
+            cache.insert(wire_content_id, verts.clone());
         }
-        cache.insert(wire_content_id, verts.clone());
+        *self.last_sdf_text.borrow_mut() = Some((self.geometry_epoch, verts.clone()));
         verts
     }