From 79cb7fd4bc1ceb03db0e7937b75bf83b7ff663bf Mon Sep 17 00:00:00 2001
From: OrcaWin <alpha-eng@stably.ai>
Date: Fri, 23 Oct 2026 15:56:16 -0700
Subject: [PATCH] fix(editor): avoid redundant CRLF normalization when syncing
 Monaco (#32583)

* fix(editor): reuse unchanged model text before EOL normalization

* fix(editor): preserve paired CRLF separators during live updates

* test(editor): drop the Monaco content-sync heap probe

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

---------

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>
---
 .../editor/monaco-content-sync.test.ts        | 21 +++++++++++++++++++
 .../components/editor/monaco-content-sync.ts  | 15 ++++++++-----
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/src/renderer/src/components/editor/monaco-content-sync.test.ts b/src/renderer/src/components/editor/monaco-content-sync.test.ts
index 30f833d379c..96996207963 100644
--- a/src/renderer/src/components/editor/monaco-content-sync.test.ts
+++ b/src/renderer/src/components/editor/monaco-content-sync.test.ts
@@ -102,6 +102,27 @@ describe('monaco content sync', () => {
   })
 
   it.each([
+    [
+      'CRLF file content into a CRLF model',
+      'first\r\nsecond\r\nlast',
+      '\r\n',
+      'first\r\nsecond\r\nlast\r\nnext',
+      '\r\nnext'
+    ],
+    [
+      'mixed file content into a CRLF model',
+      'first\r\nsecond\r\nlast',
+      '\r\n',
+      'first\r\nsecond\rlast\nnext',
+      '\r\nnext'
+    ],
+    [
+      'adjacent bare and paired CRs into a CRLF model',
+      'first\r\nsecond\r\nlast',
+      '\r\n',
+      'first\r\nsecond\r\nlast\r\r\n\nnext\r',
+      '\r\n\r\n\r\nnext\r\n'
+    ],
     [
       'CRLF file content into an LF model',
       'first\nsecond\nlast',
diff --git a/src/renderer/src/components/editor/monaco-content-sync.ts b/src/renderer/src/components/editor/monaco-content-sync.ts
index fa19928b89d..60bf36107b4 100644
--- a/src/renderer/src/components/editor/monaco-content-sync.ts
+++ b/src/renderer/src/components/editor/monaco-content-sync.ts
@@ -2,14 +2,19 @@ import type { editor } from 'monaco-editor'
 
 export type MonacoContentSyncMode = 'undoable' | 'read-only-live-tail'
 
-function normalizeToModelEol(content: string, model: editor.ITextModel): string {
+function normalizeToModelEol(
+  content: string,
+  model: editor.ITextModel,
+  currentContent: string
+): string {
   const eol = model.getEOL()
   // Why: Monaco normalizes model line endings, while filesystem content keeps
   // its raw EOLs. Compare the representation Monaco can actually retain.
-  if (eol === '\n' && !content.includes('\r')) {
+  if ((eol === '\n' && !content.includes('\r')) || content === currentContent) {
     return content
   }
-  return content.replace(/\r\n|\r|\n/g, eol)
+  const separators = eol === '\r\n' ? /\r(?!\n)|(?<!\r)\n/g : /\r\n|\r|\n/g
+  return content.replace(separators, eol)
 }
 
 function applyModelEdit(
@@ -69,7 +74,7 @@ export function syncContentOnMount(
     return false
   }
   const currentContent = model.getValue()
-  const normalizedContent = normalizeToModelEol(content, model)
+  const normalizedContent = normalizeToModelEol(content, model, currentContent)
   if (currentContent === normalizedContent) {
     return false
   }
@@ -98,7 +103,7 @@ export function syncContentUpdate(
     return
   }
   const currentContent = model.getValue()
-  const normalizedContent = normalizeToModelEol(content, model)
+  const normalizedContent = normalizeToModelEol(content, model, currentContent)
   if (currentContent.length === normalizedContent.length) {
     replaceModelContent(editorInstance, model, currentContent, normalizedContent, mode, true)
     return