fix(macOS): prevent Replace crash when search highlight ranges are stale after body edits

macOS/SynapseNotes/EditorView.swift

@@ -2719,10 +2719,20 @@ class LinkAwareTextView: NSTextView {
 
     private func replaceCurrentMatch(query: String, focusIndex: Int, replacement: String, advanceAfter: Bool) {
         guard !query.isEmpty,
-              lastSearchHighlightRanges.indices.contains(focusIndex) else { return }
-        let range = lastSearchHighlightRanges[focusIndex]
+              lastSearchHighlightRanges.indices.contains(focusIndex),
+              let storage = textStorage else { return }
+        var range = lastSearchHighlightRanges[focusIndex]
+        // Body edits do not repost the find query; debounced restyle only skips stale highlight
+        // ranges in `reapplySearchHighlights` without shrinking `lastSearchHighlightRanges`.
+        // Replacing with an out-of-bounds NSRange throws NSRangeException — resync first.
+        if NSMaxRange(range) > storage.length {
+            applySearchHighlights(query: query, focusIndex: focusIndex)
+            guard lastSearchHighlightRanges.indices.contains(focusIndex) else { return }
+            range = lastSearchHighlightRanges[focusIndex]
+            guard NSMaxRange(range) <= storage.length else { return }
+        }
         guard shouldChangeText(in: range, replacementString: replacement) else { return }
-        textStorage?.replaceCharacters(in: range, with: replacement)
+        storage.replaceCharacters(in: range, with: replacement)
         didChangeText()
 
         // Recompute matches against new text. Anchor on the position of the replacement

macOS/SynapseNotesTests/EditorViewPendingStateConsumptionTests.swift

@@ -91,4 +91,42 @@ final class EditorViewPendingStateConsumptionTests: XCTestCase {
         let maxOffset = max(0, textView.bounds.height - scrollView.contentView.bounds.height)
         XCTAssertEqual(scrollView.contentView.bounds.origin.y, maxOffset, accuracy: 0.5)
     }
+
+    /// Editing the note while the find bar stays open does not repost `scrollToSearchMatch`.
+    /// Debounced markdown restyle re-applies highlights but skips out-of-bounds cached ranges
+    /// without removing them, so Replace must not call `replaceCharacters` with a stale NSRange.
+    func test_replaceCurrentMatch_doesNotCrashWhenCachedHighlightRangeIsStaleAfterBodyEdit() {
+        let textView = RawEditor.configuredTextView(isEditable: true, settings: nil)
+        textView.participatesInGlobalSearch = true
+        textView.installSearchObservers()
+
+        textView.setPlainText("aaaaaaaaaahello")
+        NotificationCenter.default.post(
+            name: .scrollToSearchMatch,
+            object: nil,
+            userInfo: [SearchMatchKey.query: "hello", SearchMatchKey.matchIndex: 0]
+        )
+
+        guard let storage = textView.textStorage else {
+            XCTFail("expected text storage")
+            return
+        }
+        storage.beginEditing()
+        storage.replaceCharacters(in: NSRange(location: 0, length: storage.length), with: "no")
+        storage.endEditing()
+        textView.didChangeText()
+
+        NotificationCenter.default.post(
+            name: .replaceCurrentMatch,
+            object: nil,
+            userInfo: [
+                SearchMatchKey.query: "hello",
+                SearchMatchKey.matchIndex: 0,
+                SearchMatchKey.replacement: "x",
+                SearchMatchKey.advanceAfter: false,
+            ]
+        )
+
+        XCTAssertEqual(textView.string, "no")
+    }
 }