Fix editor find freezing on long documents

In-document search (Ctrl+F) blocked the UI for several seconds while
typing in long documents. Two compounding causes:

- The find command ran a full-document search and highlight rebuild on
  every keystroke. Debounce it so typing stays responsive; the input
  value still updates immediately and pending searches are flushed when
  navigating between matches.

- search() de-duplicated matches with an O(n) scan of all prior results
  per match, making a common term that matches many times quadratic.
  Track seen positions in a Set for constant-time lookups.

app/editor/components/FindAndReplace.tsx

@@ -1,3 +1,4 @@
+import { debounce } from "es-toolkit/compat";
 import {
   CaretDownIcon,
   CaretUpIcon,
@@ -211,9 +212,32 @@ export default function FindAndReplace({
     });
   }, [caseSensitive, editor.commands, searchTerm]);
 
+  // Searching the document on every keystroke is expensive in long documents –
+  // it traverses the entire doc and rebuilds highlights – so debounce it to keep
+  // typing in the input responsive. The input value itself updates immediately.
+  const debouncedFind = React.useMemo(
+    () =>
+      debounce(
+        (attrs: {
+          text: string;
+          caseSensitive: boolean;
+          regexEnabled: boolean;
+        }) => {
+          editor.commands.find(attrs);
+        },
+        250
+      ),
+    [editor.commands]
+  );
+
+  React.useEffect(() => () => debouncedFind.cancel(), [debouncedFind]);
+
   const handleKeyDown = React.useCallback(
     (ev: React.KeyboardEvent<HTMLInputElement>) => {
       function nextPrevious() {
+        // Ensure any pending debounced search has run so navigation acts on the
+        // results for the text currently in the input.
+        debouncedFind.flush();
         if (ev.shiftKey) {
           editor.commands.prevSearchMatch();
         } else {
@@ -243,7 +267,7 @@ export default function FindAndReplace({
         }
       }
     },
-    [editor.commands, selectInputText]
+    [debouncedFind, editor.commands, selectInputText]
   );
 
   const handleReplace = React.useCallback(
@@ -274,13 +298,13 @@ export default function FindAndReplace({
       ev.stopPropagation();
       setSearchTerm(ev.currentTarget.value);
 
-      editor.commands.find({
+      debouncedFind({
         text: ev.currentTarget.value,
         caseSensitive,
         regexEnabled,
       });
     },
-    [caseSensitive, editor.commands, regexEnabled]
+    [caseSensitive, debouncedFind, regexEnabled]
   );
 
   const handleReplaceKeyDown = React.useCallback(

app/editor/extensions/FindAndReplace.tsx

@@ -381,6 +381,11 @@ export default class FindAndReplaceExtension extends Extension<FindAndReplaceOpt
       }
     });
 
+    // Tracks already-seen match positions so duplicate matches (possible because
+    // we search the deburred text concatenated with the original) can be skipped
+    // in constant time rather than rescanning the entire results array.
+    const seen = new Set<string>();
+
     mergedTextNodes.forEach((node) => {
       const { text = "", pos, type } = node;
       try {
@@ -407,9 +412,11 @@ export default class FindAndReplaceExtension extends Extension<FindAndReplaceOpt
 
           // Check if already exists in results, possible due to duplicated
           // search string on L257
-          if (this.results.some((r) => r.from === from && r.to === to)) {
+          const key = `${from}:${to}`;
+          if (seen.has(key)) {
             continue;
           }
+          seen.add(key);
 
           this.results.push({ from, to, type });
         }