perf: stop scanning every entity for associative centers on each edit

The spans put it exactly: 63.5 ms of a 63.8 ms pointer-up is
`bump_entities`, and inside it two drawing-wide scans.

`refresh_associative_centerlines` and `refresh_associative_center_marks`
each walk all 1 166 357 entities, filter to Lines and parse every one's
extended data looking for an association that references a changed
handle. About 30 ms each, run on every edit -- to find, on this drawing,
none at all.

Track whether the document holds any such association. The question is
settled once, with a single pass, and after that each edit only examines
the handles it actually changed: an entity that carries an association
flips the answer to yes, and nothing else can. Deleting the last one
leaves the answer at yes, which costs a scan that finds nothing rather
than skipping one it should have run. A coarse `bump_geometry` re-opens
the question, since it can carry a new document.

Where an association really exists the scans run exactly as before.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/scene/centerline.rs

@@ -435,3 +435,15 @@ pub(crate) fn center_measure_is_relative(specification: &str) -> bool {
     let text = specification.trim();
     text.eq_ignore_ascii_case("ByLineType") || text.ends_with(['x', 'X'])
 }
+
+/// Whether `entity` carries a centerline association.
+///
+/// Used to keep the drawing-wide scan off the edit path: only an entity that
+/// actually carries one can make the scan necessary.
+pub(crate) fn entity_has_center_association(entity: &EntityType) -> bool {
+    let EntityType::Line(line) = entity else {
+        return false;
+    };
+    CenterLineAssociation::read(&line.common.extended_data)
+        .is_some_and(|association| association.associated)
+}

src/scene/centermark.rs

@@ -473,3 +473,15 @@ impl Scene {
         candidates.len()
     }
 }
+
+/// Whether `entity` carries a center mark association.
+///
+/// Used to keep the drawing-wide scan off the edit path: only an entity that
+/// actually carries one can make the scan necessary.
+pub(crate) fn entity_has_center_association(entity: &EntityType) -> bool {
+    let EntityType::Line(line) = entity else {
+        return false;
+    };
+    CenterMarkAssociation::read(&line.common.extended_data)
+        .is_some_and(|association| association.associated)
+}

src/scene/mod.rs

@@ -1827,6 +1827,15 @@ pub struct Scene {
     /// Boundary source → associative hatch handles. Source edits reuse this
     /// index instead of scanning the document during every drag step.
     associative_hatch_source_cache: RefCell<Option<HashMap<Handle, Vec<Handle>>>>,
+    /// Whether the drawing contains any associative centerline or center mark.
+    ///
+    /// Refreshing those means scanning every entity and parsing its extended
+    /// data — 1.17 M entities and ~30 ms each on the reproducer, run twice on
+    /// every edit, to find none at all. `None` means not yet determined; the
+    /// first scan records the answer, and later edits only re-examine the
+    /// handles they actually changed. Staying `true` after the last one is
+    /// deleted is merely slower, never wrong.
+    has_associative_centers: std::cell::Cell<Option<bool>>,
     /// Tessellated block definitions in block-local coords, keyed by render
     /// background and block epoch. Model and Paper adapt black/white colours
     /// differently; retaining both variants prevents a full block rebuild on
@@ -2057,6 +2066,7 @@ impl Scene {
             layout_type_names_cache: RefCell::new(None),
             dependency_index_cache: RefCell::new(None),
             associative_hatch_source_cache: RefCell::new(None),
+            has_associative_centers: std::cell::Cell::new(None),
             block_defn_cache: RefCell::new(HashMap::default()),
             entity_index_cache: RefCell::new(None),
             last_render_aspect: std::cell::Cell::new(16.0 / 9.0),
@@ -2531,6 +2541,35 @@ impl Scene {
         changes
     }
 
+    /// Whether the associative centerline / center-mark scans can be skipped.
+    ///
+    /// Answers from the cached hint when it is known, and otherwise from the
+    /// changed entities alone: if any of them carries an association the hint
+    /// flips to `true` and the scans run from then on. Only an undetermined
+    /// hint costs a full pass, and that happens once.
+    fn associative_centers_possible(&self, changes: &[(Handle, ChangeKind)]) -> bool {
+        if changes.iter().any(|(handle, _)| {
+            self.document.get_entity(*handle).is_some_and(|entity| {
+                crate::scene::centerline::entity_has_center_association(entity)
+                    || crate::scene::centermark::entity_has_center_association(entity)
+            })
+        }) {
+            self.has_associative_centers.set(Some(true));
+            return true;
+        }
+        if let Some(known) = self.has_associative_centers.get() {
+            return known;
+        }
+        // Undetermined: settle it with one pass over the drawing, then never
+        // again for this document.
+        let any = self.document.entities().any(|entity| {
+            crate::scene::centerline::entity_has_center_association(entity)
+                || crate::scene::centermark::entity_has_center_association(entity)
+        });
+        self.has_associative_centers.set(Some(any));
+        any
+    }
+
     pub fn bump_entities(&mut self, changes: &[(Handle, ChangeKind)]) {
         if changes.iter().any(|(handle, kind)| {
             matches!(kind, ChangeKind::Removed)
@@ -2542,14 +2581,16 @@ impl Scene {
             self.associative_hatch_source_cache.borrow_mut().take();
         }
         let mut changes = changes.to_vec();
-        for change in self.refresh_associative_centerlines(&changes) {
-            if !changes.iter().any(|(handle, _)| *handle == change.0) {
-                changes.push(change);
+        if self.associative_centers_possible(&changes) {
+            for change in self.refresh_associative_centerlines(&changes) {
+                if !changes.iter().any(|(handle, _)| *handle == change.0) {
+                    changes.push(change);
+                }
             }
-        }
-        for change in self.refresh_associative_center_marks(&changes) {
-            if !changes.iter().any(|(handle, _)| *handle == change.0) {
-                changes.push(change);
+            for change in self.refresh_associative_center_marks(&changes) {
+                if !changes.iter().any(|(handle, _)| *handle == change.0) {
+                    changes.push(change);
+                }
             }
         }
         for change in self.refresh_associative_dimensions(&changes) {
@@ -2662,6 +2703,9 @@ impl Scene {
         // Default: also invalidate block definitions. Safe for every caller;
         // operations that know blocks are untouched use `bump_geometry_no_blocks`.
         self.block_epoch = GEOMETRY_EPOCH.fetch_add(1, Ordering::Relaxed);
+        // A change this coarse can carry a new document; re-determine whether
+        // it holds associative centerlines or center marks.
+        self.has_associative_centers.set(None);
         // Structural change — drop both per-entity tessellation memos.
         self.tess_memo.borrow_mut().clear();
         self.resident_tess_memo.borrow_mut().clear();