perf(core): trim per-keypress waste on the focus and state path

src/core/elementNode.ts

@@ -1542,7 +1542,14 @@ export class ElementNode {
 
     const states = this.states;
 
-    if (this._undoStyles || keyExists(this, states)) {
+    // An empty _undoStyles (left behind once a state style has been undone)
+    // must not force the resolution branch: with nothing to undo and no style
+    // matching any active state, the branch provably assigns nothing, and it
+    // runs on every path element of every focus change.
+    if (
+      (this._undoStyles !== undefined && this._undoStyles.length > 0) ||
+      keyExists(this, states)
+    ) {
       let stylesToUndo: { [key: string]: any } | undefined;
       if (this._undoStyles && this._undoStyles.length) {
         stylesToUndo = {};

src/core/focusManager.ts

@@ -228,8 +228,10 @@ const updateFocusPath = (
   prevFocusedElm: ElementNode | undefined,
 ) => {
   let current: ElementNode | undefined = currentFocusedElm;
+  // fp escapes through the focusPath signal, so it must be a fresh array; the
+  // membership test below runs on paths of a handful of elements every single
+  // keypress, where a linear scan beats allocating and hashing a Set.
   const fp: ElementNode[] = [];
-  const fpSet = new Set<ElementNode>();
   while (current) {
     if (
       !current.states.has(Config.focusStateKey) ||
@@ -251,13 +253,13 @@ const updateFocusPath = (
       );
     }
     fp.push(current);
-    fpSet.add(current);
     current = current.parent;
   }
 
   const prevFp = focusPath();
-  prevFp.forEach((elm) => {
-    if (!fpSet.has(elm)) {
+  for (let i = 0; i < prevFp.length; i++) {
+    const elm = prevFp[i]!;
+    if (fp.indexOf(elm) === -1) {
       elm.states.remove(Config.focusStateKey);
       elm.onBlur?.call(elm, currentFocusedElm, prevFocusedElm!, elm);
       elm.onFocusChanged?.call(
@@ -268,7 +270,7 @@ const updateFocusPath = (
         elm,
       );
     }
-  });
+  }
 
   if (Config.focusDebug) {
     addFocusDebug(prevFp, fp);

src/core/states.ts

@@ -26,8 +26,17 @@ export default class States extends Array<DollarString> {
   }
 
   has(state: DollarString) {
-    // temporary check for $ prefix
-    return this.indexOf(state) >= 0 || this.indexOf(`$${state}`) >= 0;
+    if (this.indexOf(state) >= 0) {
+      return true;
+    }
+    // temporary check for $ prefix, so has('focus') matches '$focus'. A query
+    // that already starts with '$' could only match a doubled prefix, which
+    // nothing produces, so skip the lookup: this runs per path element on
+    // every focus change and the template string was a per-call allocation.
+    return (
+      state.charCodeAt(0) !== 36 &&
+      this.indexOf(('$' + state) as DollarString) >= 0
+    );
   }
 
   is(state: DollarString) {