fix(buffer): avoid shared _extendedAttrs sentinel breaking addon-image

EMPTY_SPARSE_EXTENDED was shared across lines via copyFrom; addon-image
writes _extendedAttrs directly without copy-on-write, which caused tile
eviction failures and broke instanceof Object checks.

Use undefined for empty extended maps (keep EMPTY_SPARSE_MAP for _combined).
Ensure addon-image forks the map before writes and update the accessor test.

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

README.md

@@ -254,7 +254,6 @@ Xterm.js is used in many world-class applications to provide great terminal expe
 - [**WooTTY**](https://github.com/icoretech/wootty): Flawless browser terminal for real operators.
 - [**Orca**](https://github.com/stablyai/orca): Agentic development environment for 100x builders.
 - [**4bit**](https://ciembor.github.io/4bit): Terminal Color Scheme Designer.
-- [**Cate**](https://github.com/0-AI-UG/cate): Open source desktop IDE on an infinite zoomable canvas. Editor, browser, and terminal panels float in spatial space; the terminals are xterm.js with the WebGL addon, backed by node-pty.
 - [And much more...](https://github.com/xtermjs/xterm.js/network/dependents?package_id=UGFja2FnZS0xNjYzMjc4OQ%3D%3D)
 
 Do you use xterm.js in your application as well? Please [open a Pull Request](https://github.com/sourcelair/xterm.js/pulls) to include it here. We would love to have it on our list. Please add any new contributions to the end of the list.

addons/addon-image/src/ImageStorage.ts

@@ -436,9 +436,9 @@ export class ImageStorage implements IDisposable {
       for (let col = 0; col < cols; ++col) {
         let e: IExtendedAttrsImage;
         if (line.getBg(col) & BgFlags.HAS_EXTENDED) {
-          e = line._extendedAttrs[col] ?? EMPTY_ATTRS;
+          e = line._extendedAttrs?.[col] ?? EMPTY_ATTRS;
         } else {
-          const maybeImg = line._extendedAttrs[col] as IExtendedAttrsImage | undefined;
+          const maybeImg = line._extendedAttrs?.[col] as IExtendedAttrsImage | undefined;
           if (!maybeImg || maybeImg.imageId === undefined || maybeImg.imageId === -1) {
             continue;
           }
@@ -461,7 +461,7 @@ export class ImageStorage implements IDisposable {
            * Also check _extendedAttrs directly for cells where text cleared HAS_EXTENDED.
            */
           while (++col < cols) {
-            const nextE = line._extendedAttrs[col] as IExtendedAttrsImage | undefined;
+            const nextE = line._extendedAttrs?.[col] as IExtendedAttrsImage | undefined;
             if (!nextE || nextE.imageId !== imageId || nextE.tileId !== startTile + count) {
               break;
             }
@@ -515,7 +515,7 @@ export class ImageStorage implements IDisposable {
     for (let row = 0; row < rows; ++row) {
       const line = buffer.lines.get(row) as IBufferLineExt;
       if (line.getBg(oldCol) & BgFlags.HAS_EXTENDED) {
-        const e: IExtendedAttrsImage = line._extendedAttrs[oldCol] ?? EMPTY_ATTRS;
+        const e: IExtendedAttrsImage = line._extendedAttrs?.[oldCol] ?? EMPTY_ATTRS;
         const imageId = e.imageId;
         if (imageId === undefined || imageId === -1) {
           continue;
@@ -560,7 +560,7 @@ export class ImageStorage implements IDisposable {
     const buffer = this._terminal._core.buffer;
     const line = buffer.lines.get(y) as IBufferLineExt;
     if (line && line.getBg(x) & BgFlags.HAS_EXTENDED) {
-      const e: IExtendedAttrsImage = line._extendedAttrs[x] ?? EMPTY_ATTRS;
+      const e: IExtendedAttrsImage = line._extendedAttrs?.[x] ?? EMPTY_ATTRS;
       if (e.imageId && e.imageId !== -1) {
         const orig = this._images.get(e.imageId)?.orig;
         if (window.ImageBitmap && orig instanceof ImageBitmap) {
@@ -580,7 +580,7 @@ export class ImageStorage implements IDisposable {
     const buffer = this._terminal._core.buffer;
     const line = buffer.lines.get(y) as IBufferLineExt;
     if (line && line.getBg(x) & BgFlags.HAS_EXTENDED) {
-      const e: IExtendedAttrsImage = line._extendedAttrs[x] ?? EMPTY_ATTRS;
+      const e: IExtendedAttrsImage = line._extendedAttrs?.[x] ?? EMPTY_ATTRS;
       if (e.imageId && e.imageId !== -1 && e.tileId !== -1) {
         const spec = this._images.get(e.imageId);
         if (spec) {
@@ -611,7 +611,7 @@ export class ImageStorage implements IDisposable {
 
   private _writeToCell(line: IBufferLineExt, x: number, imageId: number, tileId: number): void {
     if (line._data[x * Cell.SIZE + Cell.BG] & BgFlags.HAS_EXTENDED) {
-      const old = line._extendedAttrs[x];
+      const old = line._extendedAttrs?.[x];
       if (old) {
         if (old.imageId !== undefined) {
           // found an old ExtendedAttrsImage, since we know that
@@ -627,13 +627,13 @@ export class ImageStorage implements IDisposable {
           return;
         }
         // found a plain ExtendedAttrs instance, clone it to new entry
-        line._extendedAttrs[x] = new ExtendedAttrsImage(old.ext, old.urlId, imageId, tileId);
+        (line._extendedAttrs ??= {})[x] = new ExtendedAttrsImage(old.ext, old.urlId, imageId, tileId);
         return;
       }
     }
     // fall-through: always create new ExtendedAttrsImage entry
     line._data[x * Cell.SIZE + Cell.BG] |= BgFlags.HAS_EXTENDED;
-    line._extendedAttrs[x] = new ExtendedAttrsImage(0, 0, imageId, tileId);
+    (line._extendedAttrs ??= {})[x] = new ExtendedAttrsImage(0, 0, imageId, tileId);
   }
 
   private _evictOnAlternate(): void {
@@ -652,7 +652,7 @@ export class ImageStorage implements IDisposable {
       }
       for (let x = 0; x < this._terminal.cols; ++x) {
         if (line._data[x * Cell.SIZE + Cell.BG] & BgFlags.HAS_EXTENDED) {
-          const imgId = line._extendedAttrs[x]?.imageId;
+          const imgId = line._extendedAttrs?.[x]?.imageId;
           if (imgId) {
             const spec = this._images.get(imgId);
             if (spec) {

addons/addon-image/src/Types.ts

@@ -64,7 +64,7 @@ export interface IExtendedAttrsImage extends IExtendedAttrs {
 
 /* eslint-disable */
 export interface IBufferLineExt extends IBufferLine {
-  _extendedAttrs: {[index: number]: IExtendedAttrsImage | undefined};
+  _extendedAttrs: {[index: number]: IExtendedAttrsImage | undefined} | undefined;
   _data: Uint32Array;
 }
 

addons/addon-image/test/ImageAddon.test.ts

@@ -118,7 +118,10 @@ test.describe('ImageAddon', () => {
     }
     // bufferline privates
     strictEqual(await ctx.page.evaluate('window.term._core.buffer.lines.get(0)._data instanceof Uint32Array'), true);
-    strictEqual(await ctx.page.evaluate('window.term._core.buffer.lines.get(0)._extendedAttrs instanceof Object'), true);
+    strictEqual(await ctx.page.evaluate(`(() => {
+      const ea = window.term._core.buffer.lines.get(0)._extendedAttrs;
+      return ea === undefined || (typeof ea === 'object' && ea !== null);
+    })()`), true);
     // inputhandler privates
     strictEqual(await ctx.page.evaluate('window.term._core._inputHandler._curAttrData.constructor.name'), '_AttributeData');
     strictEqual(await ctx.page.evaluate('window.term._core._inputHandler._parser.constructor.name'), 'EscapeSequenceParser');

addons/addon-search/src/SearchAddon.ts

@@ -142,14 +142,12 @@ export class SearchAddon extends Disposable implements ITerminalAddon, ISearchAp
       }
       prevResult = result;
       results.push(prevResult);
-      const cols = this._terminal.cols;
+      result = this._engine.find(
-      let nextCol = prevResult.col + prevResult.size;
+        term,
-      let nextRow = prevResult.row;
+        prevResult.col + prevResult.term.length >= this._terminal.cols ? prevResult.row + 1 : prevResult.row,
-      if (nextCol >= cols) {
+        prevResult.col + prevResult.term.length >= this._terminal.cols ? 0 : prevResult.col + 1,
-        nextRow += Math.floor(nextCol / cols);
+        searchOptions
-        nextCol = nextCol % cols;
+      );
-      }
-      result = this._engine.find(term, nextRow, nextCol, searchOptions);
     }
 
     this._resultTracker.updateResults(results, this._highlightLimit);

addons/addon-search/test/SearchAddon.test.ts

@@ -414,20 +414,6 @@ test.describe('Search Tests', () => {
   });
 
   test.describe('Regression tests', () => {
-    test('should advance highlight-all scan by buffer match size for wide characters', async () => {
-      await ctx.page.evaluate(`
-        window.calls = [];
-        window.search.onDidChangeResults(e => window.calls.push(e));
-      `);
-      await ctx.proxy.resize(3, 5);
-      await ctx.proxy.write('𝄞𝄞𝄞');
-      strictEqual(await ctx.page.evaluate(`window.search.findNext('𝄞', { decorations: { activeMatchColorOverviewRuler: '#ff0000', matchOverviewRuler: '#ffff00' } })`), true);
-      deepStrictEqual(await ctx.page.evaluate('window.calls'), [
-        { resultCount: 3, resultIndex: 0 }
-      ]);
-      await ctx.proxy.resize(80, 24);
-    });
-
     test.describe('#2444 wrapped line content not being found', () => {
       let fixture: string;
       test.beforeAll(async () => {

package-lock.json

@@ -663,9 +663,9 @@
       }
     },
     "node_modules/@esbuild/aix-ppc64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.28.0.tgz",
-      "integrity": "sha512-Svl7tq8k/08+p6CXPpRjQ1fKX+1odH/BQbb48fV6fj3CWHhsoIOoY87w1oHXm0qEpkIK3ZfVgp0hed3XBXzXMQ==",
+      "integrity": "sha512-lhRUCeuOyJQURhTxl4WkpFTjIsbDayJHih5kZC1giwE+MhIzAb7mEsQMqMf18rHLsrb5qI1tafG20mLxEWcWlA==",
       "cpu": [
         "ppc64"
       ],
@@ -680,9 +680,9 @@
       }
     },
     "node_modules/@esbuild/android-arm": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/android-arm/-/android-arm-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/android-arm/-/android-arm-0.28.0.tgz",
-      "integrity": "sha512-0k2F129Xdio1TdJfzJ8sy1Q47vUD2NnwdhiAf7drUN1EBTfPf4hsFCtmMgu/6m8JSzsBrlmVjudMBQqOfG8usQ==",
+      "integrity": "sha512-wqh0ByljabXLKHeWXYLqoJ5jKC4XBaw6Hk08OfMrCRd2nP2ZQ5eleDZC41XHyCNgktBGYMbqnrJKq/K/lzPMSQ==",
       "cpu": [
         "arm"
       ],
@@ -697,9 +697,9 @@
       }
     },
     "node_modules/@esbuild/android-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/android-arm64/-/android-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/android-arm64/-/android-arm64-0.28.0.tgz",
-      "integrity": "sha512-34EGEbCIAgosYz6goLcopX6Mo7NyGv9tfwEM2/7Ce2VcVRk568iSvniGWcUXIy7wEDR1wzolcxcriFVrWYcwBg==",
+      "integrity": "sha512-+WzIXQOSaGs33tLEgYPYe/yQHf0WTU0X42Jca3y8NWMbUVhp7rUnw+vAsRC/QiDrdD31IszMrZy+qwPOPjd+rw==",
       "cpu": [
         "arm64"
       ],
@@ -714,9 +714,9 @@
       }
     },
     "node_modules/@esbuild/android-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/android-x64/-/android-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/android-x64/-/android-x64-0.28.0.tgz",
-      "integrity": "sha512-dbwY7ltSMDWsRatcRpCnES4F+im88OCUgGZjy52shC7GqHRE/cYlxNbB4Z4UpJswpcc4Qxd2oE/ufM0p61IKng==",
+      "integrity": "sha512-+VJggoaKhk2VNNqVL7f6S189UzShHC/mR9EE8rDdSkdpN0KflSwWY/gWjDrNxxisg8Fp1ZCD9jLMo4m0OUfeUA==",
       "cpu": [
         "x64"
       ],
@@ -731,9 +731,9 @@
       }
     },
     "node_modules/@esbuild/darwin-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/darwin-arm64/-/darwin-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/darwin-arm64/-/darwin-arm64-0.28.0.tgz",
-      "integrity": "sha512-TZbWkQY7kvTAXbXUT7uVACR5cMHsDiSz9z7ZKAX/RTq/WJEk3QyRr0wZpNhBDX+/0CtdqUIJlOiodQcta6tY3Q==",
+      "integrity": "sha512-0T+A9WZm+bZ84nZBtk1ckYsOvyA3x7e2Acj1KdVfV4/2tdG4fzUp91YHx+GArWLtwqp77pBXVCPn2We7Letr0Q==",
       "cpu": [
         "arm64"
       ],
@@ -748,9 +748,9 @@
       }
     },
     "node_modules/@esbuild/darwin-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/darwin-x64/-/darwin-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/darwin-x64/-/darwin-x64-0.28.0.tgz",
-      "integrity": "sha512-zfdzgK9ACBNZLI/CyHTOx81SyNbM6YXn7rxSgX97VjyiPl9W1i4Ka4fgKECEoFCKGpvBj5qArWIGgQjOwkgskQ==",
+      "integrity": "sha512-fyzLm/DLDl/84OCfp2f/XQ4flmORsjU7VKt8HLjvIXChJoFFOIL6pLJPH4Yhd1n1gGFF9mPwtlN5Wf82DZs+LQ==",
       "cpu": [
         "x64"
       ],
@@ -765,9 +765,9 @@
       }
     },
     "node_modules/@esbuild/freebsd-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/freebsd-arm64/-/freebsd-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/freebsd-arm64/-/freebsd-arm64-0.28.0.tgz",
-      "integrity": "sha512-wG2EA8ENdEI0qhkSZMjfqrdY+ziCYCPMmtZjjIwOmXFjmyzEHn+UUxk5of+SYsjtfs3VpnlC7QLzSI5hY/rOAw==",
+      "integrity": "sha512-l9GeW5UZBT9k9brBYI+0WDffcRxgHQD8ShN2Ur4xWq/NFzUKm3k5lsH4PdaRgb2w7mI9u61nr2gI2mLI27Nh3Q==",
       "cpu": [
         "arm64"
       ],
@@ -782,9 +782,9 @@
       }
     },
     "node_modules/@esbuild/freebsd-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/freebsd-x64/-/freebsd-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/freebsd-x64/-/freebsd-x64-0.28.0.tgz",
-      "integrity": "sha512-i7dZ9vQgnvSCzi/rYCXNgtF/U+eKZNJBzu3eTQbRgHnM7tNSizLOkRFAl3qzVc/Op/u5YkHHa4pf/3DOYHthLQ==",
+      "integrity": "sha512-BXoQai/A0wPO6Es3yFJ7APCiKGc1tdAEOgeTNy3SsB491S3aHn4S4r3e976eUnPdU+NbdtmBuLncYir2tMU9Nw==",
       "cpu": [
         "x64"
       ],
@@ -799,9 +799,9 @@
       }
     },
     "node_modules/@esbuild/linux-arm": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-arm/-/linux-arm-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-arm/-/linux-arm-0.28.0.tgz",
-      "integrity": "sha512-qVXBOHQS+d5Y722GwJzJUtOLlX7km3CraOaGormF1pDtPd2C/l1SHRPgjLunLGe51Sh5YYWKMFDyV4SxgMQYTQ==",
+      "integrity": "sha512-CjaaREJagqJp7iTaNQjjidaNbCKYcd4IDkzbwwxtSvjI7NZm79qiHc8HqciMddQ6CKvJT6aBd8lO9kN/ZudLlw==",
       "cpu": [
         "arm"
       ],
@@ -816,9 +816,9 @@
       }
     },
     "node_modules/@esbuild/linux-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-arm64/-/linux-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-arm64/-/linux-arm64-0.28.0.tgz",
-      "integrity": "sha512-yHs+0uc8+nvEAfAfxrWQKK5peSNzBc4PegcMO0EJ2hT71uA7vB8Ihg2e77R2P7SG5uYjPbHlLLmve4LLLRCf0g==",
+      "integrity": "sha512-RVyzfb3FWsGA55n6WY0MEIEPURL1FcbhFE6BffZEMEekfCzCIMtB5yyDcFnVbTnwk+CLAgTujmV/Lgvih56W+A==",
       "cpu": [
         "arm64"
       ],
@@ -833,9 +833,9 @@
       }
     },
     "node_modules/@esbuild/linux-ia32": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-ia32/-/linux-ia32-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-ia32/-/linux-ia32-0.28.0.tgz",
-      "integrity": "sha512-d1z4ZuP0ajrfz/FhGT4vv278rX8KnPPJx8i5+AtK7TYbx9Le9F1hyzurZpkEyjkGa9dUGhQow4C1NmeGvqxN2w==",
+      "integrity": "sha512-KBnSTt1kxl9x70q+ydterVdl+Cn0H18ngRMRCEQfrbqdUuntQQ0LoMZv47uB97NljZFzY6HcfqEZ2SAyIUTQBQ==",
       "cpu": [
         "ia32"
       ],
@@ -850,9 +850,9 @@
       }
     },
     "node_modules/@esbuild/linux-loong64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-loong64/-/linux-loong64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-loong64/-/linux-loong64-0.28.0.tgz",
-      "integrity": "sha512-M5sRjUVZrkm1OAPR3dlOYzNmN+loZKGVi1VUQGrwuqLcbR6qeAz+famMhjASeH3YVKvZz+zT1jlh/keC3Rj/lg==",
+      "integrity": "sha512-zpSlUce1mnxzgBADvxKXX5sl8aYQHo2ezvMNI8I0lbblJtp8V4odlm3Yzlj7gPyt3T8ReksE6bK+pT3WD+aJRg==",
       "cpu": [
         "loong64"
       ],
@@ -867,9 +867,9 @@
       }
     },
     "node_modules/@esbuild/linux-mips64el": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-mips64el/-/linux-mips64el-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-mips64el/-/linux-mips64el-0.28.0.tgz",
-      "integrity": "sha512-mRObBZeHh2OxcBFPWE/FjylkRgZdYuiTR3vaTozquCGOH14iP9oN4x4Ge81CoIDYQrXmIxpFumJBu5MtZpnQJQ==",
+      "integrity": "sha512-2jIfP6mmjkdmeTlsX/9vmdmhBmKADrWqN7zcdtHIeNSCH1SqIoNI63cYsjQR8J+wGa4Y5izRcSHSm8K3QWmk3w==",
       "cpu": [
         "mips64el"
       ],
@@ -884,9 +884,9 @@
       }
     },
     "node_modules/@esbuild/linux-ppc64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-ppc64/-/linux-ppc64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-ppc64/-/linux-ppc64-0.28.0.tgz",
-      "integrity": "sha512-slScBsMAb3GFDcdrCgLwZtPYRoH2H/youv10QiZyRjmsP48fznoveWytSgCI/R0ZcUgpc0ZhIUEx6LHts8yrfQ==",
+      "integrity": "sha512-bc0FE9wWeC0WBm49IQMPSPILRocGTQt3j5KPCA8os6VprfuJ7KD+5PzESSrJ6GmPIPJK965ZJHTUlSA6GNYEhg==",
       "cpu": [
         "ppc64"
       ],
@@ -901,9 +901,9 @@
       }
     },
     "node_modules/@esbuild/linux-riscv64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-riscv64/-/linux-riscv64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-riscv64/-/linux-riscv64-0.28.0.tgz",
-      "integrity": "sha512-kw0owk1o0GFETUJyW0jc0G4Yzs0BHZn0JDZ8JRT088vjJYX777BAs1fDGxAC+q831qOs2DTC96mNsG2opdfyyQ==",
+      "integrity": "sha512-SQPZOwoTTT/HXFXQJG/vBX8sOFagGqvZyXcgLA3NhIqcBv1BJU1d46c0rGcrij2B56Z2rNiSLaZOYW5cUk7yLQ==",
       "cpu": [
         "riscv64"
       ],
@@ -918,9 +918,9 @@
       }
     },
     "node_modules/@esbuild/linux-s390x": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-s390x/-/linux-s390x-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-s390x/-/linux-s390x-0.28.0.tgz",
-      "integrity": "sha512-/lAIjX8aYFRByhh6L5rYtPEDRqa9de/4V/juOXcta5frjvzXO4/sqEtyytse0g3zZFuWu5cDN0MkLz2qRDD2Ag==",
+      "integrity": "sha512-SCfR0HN8CEEjnYnySJTd2cw0k9OHB/YFzt5zgJEwa+wL/T/raGWYMBqwDNAC6dqFKmJYZoQBRfHjgwLHGSrn3Q==",
       "cpu": [
         "s390x"
       ],
@@ -935,9 +935,9 @@
       }
     },
     "node_modules/@esbuild/linux-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/linux-x64/-/linux-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/linux-x64/-/linux-x64-0.28.0.tgz",
-      "integrity": "sha512-u/anNYF2mmVOEDwLtnQ1wOr3EZ9sTNGLWrsYGYwHWzGA3Si84IOkHXlbWTD1NB+9/1lcnweYKO54uhxZydNzfA==",
+      "integrity": "sha512-us0dSb9iFxIi8srnpl931Nvs65it/Jd2a2K3qs7fz2WfGPHqzfzZTfec7oxZJRNPXPnNYZtanmRc4AL/JwVzHQ==",
       "cpu": [
         "x64"
       ],
@@ -952,9 +952,9 @@
       }
     },
     "node_modules/@esbuild/netbsd-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/netbsd-arm64/-/netbsd-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/netbsd-arm64/-/netbsd-arm64-0.28.0.tgz",
-      "integrity": "sha512-oks0DYbLwWMmaakTsCb+zL4E+aHRVLom9IJZOAthMQEPiQmydXHkziYEsGYRx0uNV/IjEKGAV941JzH02pflqw==",
+      "integrity": "sha512-CR/RYotgtCKwtftMwJlUU7xCVNg3lMYZ0RzTmAHSfLCXw3NtZtNpswLEj/Kkf6kEL3Gw+BpOekRX0BYCtklhUw==",
       "cpu": [
         "arm64"
       ],
@@ -969,9 +969,9 @@
       }
     },
     "node_modules/@esbuild/netbsd-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/netbsd-x64/-/netbsd-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/netbsd-x64/-/netbsd-x64-0.28.0.tgz",
-      "integrity": "sha512-aeL6lAnN89Hz43Mlh1G8ARasbuoYvSITDEx0tHh5b7jJnHcssqgjy9Yx430GDpmCa6OyrKoS0aNRjKundRizGg==",
+      "integrity": "sha512-nU1yhmYutL+fQ71Kxnhg8uEOdC0pwEW9entHykTgEbna2pw2dkbFSMeqjjyHZoCmt8SBkOSvV+yNmm94aUrrqw==",
       "cpu": [
         "x64"
       ],
@@ -986,9 +986,9 @@
       }
     },
     "node_modules/@esbuild/openbsd-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/openbsd-arm64/-/openbsd-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/openbsd-arm64/-/openbsd-arm64-0.28.0.tgz",
-      "integrity": "sha512-MEFJe5C3R8pwXdZ5Y21oo6m7ePiS0d9pWucn99O/wvyJZChoIQKrQDxKrGeW8F5+T0okTHesAmDeiHDTIq0V/Q==",
+      "integrity": "sha512-cXb5vApOsRsxsEl4mcZ1XY3D4DzcoMxR/nnc4IyqYs0rTI8ZKmW6kyyg+11Z8yvgMfAEldKzP7AdP64HnSC/6g==",
       "cpu": [
         "arm64"
       ],
@@ -1003,9 +1003,9 @@
       }
     },
     "node_modules/@esbuild/openbsd-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/openbsd-x64/-/openbsd-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/openbsd-x64/-/openbsd-x64-0.28.0.tgz",
-      "integrity": "sha512-i/ZLIOafE0Z8cI/XANJAixoJL/uRAoS2xOA3rb0xN+KK0K177cMAsQYkzHtBrtMXAKuAc7HGgcWiZ/sRC1Nxgw==",
+      "integrity": "sha512-8wZM2qqtv9UP3mzy7HiGYNH/zjTA355mpeuA+859TyR+e+Tc08IHYpLJuMsfpDJwoLo1ikIJI8jC3GFjnRClzA==",
       "cpu": [
         "x64"
       ],
@@ -1020,9 +1020,9 @@
       }
     },
     "node_modules/@esbuild/openharmony-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/openharmony-arm64/-/openharmony-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/openharmony-arm64/-/openharmony-arm64-0.28.0.tgz",
-      "integrity": "sha512-ge+Z7EXFNt2BO1oAMsVpiQ8EwndV9i1xXerAeTIK7AtPs3bKFXQM7nlRxDSIUIMeueR1CNXxqztLzdNeReKBJg==",
+      "integrity": "sha512-FLGfyizszcef5C3YtoyQDACyg95+dndv79i2EekILBofh5wpCa1KuBqOWKrEHZg3zrL3t5ouE5jgr94vA+Wb2w==",
       "cpu": [
         "arm64"
       ],
@@ -1037,9 +1037,9 @@
       }
     },
     "node_modules/@esbuild/sunos-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/sunos-x64/-/sunos-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/sunos-x64/-/sunos-x64-0.28.0.tgz",
-      "integrity": "sha512-BEjgtECkL3vY+SaSQ6nzVfiALUeFxpawyp8Jmf5PtYhf1Ug40N1h/hxlhts+f1FvSvarEigdxS3BlSMI2PJLcQ==",
+      "integrity": "sha512-1ZgjUoEdHZZl/YlV76TSCz9Hqj9h9YmMGAgAPYd+q4SicWNX3G5GCyx9uhQWSLcbvPW8Ni7lj4gDa1T40akdlw==",
       "cpu": [
         "x64"
       ],
@@ -1054,9 +1054,9 @@
       }
     },
     "node_modules/@esbuild/win32-arm64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/win32-arm64/-/win32-arm64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/win32-arm64/-/win32-arm64-0.28.0.tgz",
-      "integrity": "sha512-lCv9eK/H6ZJWbE7bh2nw54CZ9M2nupBxJcTsdk/QQnWkdSjKGuxmmH8/GWrlT1eMmZfn4dGcCjRte397WqfQXA==",
+      "integrity": "sha512-Q9StnDmQ/enxnpxCCLSg0oo4+34B9TdXpuyPeTedN/6+iXBJ4J+zwfQI28u/Jl40nOYAxGoNi7mFP40RUtkmUA==",
       "cpu": [
         "arm64"
       ],
@@ -1071,9 +1071,9 @@
       }
     },
     "node_modules/@esbuild/win32-ia32": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/win32-ia32/-/win32-ia32-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/win32-ia32/-/win32-ia32-0.28.0.tgz",
-      "integrity": "sha512-zvb/mB2bSCoJOpoCBgYKKpX6YM6mJBlBUVUtVj41DlZJVEB6/0CKlRYxP5wWl1C1ILiCoAU5wZZ4q1P3qeS6Eg==",
+      "integrity": "sha512-zF3ag/gfiCe6U2iczcRzSYJKH1DCI+ByzSENHlM2FcDbEeo5Zd2C86Aq0tKUYAJJ1obRP84ymxIAksZUcdztHA==",
       "cpu": [
         "ia32"
       ],
@@ -1088,9 +1088,9 @@
       }
     },
     "node_modules/@esbuild/win32-x64": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/@esbuild/win32-x64/-/win32-x64-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/@esbuild/win32-x64/-/win32-x64-0.28.0.tgz",
-      "integrity": "sha512-bm4Mowrv+GXMlpWX++EcXw/iLyd1o3+bJkC2DkWXYVvgZCqD/bSj9ctZeAMC3cIxgjRVR2Dufaiu4YPxr5gW1A==",
+      "integrity": "sha512-pEl1bO9mfAmIC+tW5btTmrKaujg3zGtUmWNdCw/xs70FBjwAL3o9OEKNHvNmnyylD6ubxUERiEhdsL0xBQ9efw==",
       "cpu": [
         "x64"
       ],
@@ -3869,9 +3869,9 @@
       "license": "MIT"
     },
     "node_modules/esbuild": {
-      "version": "0.28.1",
+      "version": "0.28.0",
-      "resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.28.0.tgz",
-      "integrity": "sha512-HrJrvZv5ayxBzPfwphOoNzkzOIIlifzk0KJrGK2c8R4+LKpMtpYLQeUdjnwjWv/LZlkH2laZk+4w78pi99D4Vw==",
+      "integrity": "sha512-sNR9MHpXSUV/XB4zmsFKN+QgVG82Cc7+/aaxJ8Adi8hyOac+EXptIp45QBPaVyX3N70664wRbTcLTOemCAnyqw==",
       "dev": true,
       "hasInstallScript": true,
       "license": "MIT",
@@ -3882,32 +3882,32 @@
         "node": ">=18"
       },
       "optionalDependencies": {
-        "@esbuild/aix-ppc64": "0.28.1",
+        "@esbuild/aix-ppc64": "0.28.0",
-        "@esbuild/android-arm": "0.28.1",
+        "@esbuild/android-arm": "0.28.0",
-        "@esbuild/android-arm64": "0.28.1",
+        "@esbuild/android-arm64": "0.28.0",
-        "@esbuild/android-x64": "0.28.1",
+        "@esbuild/android-x64": "0.28.0",
-        "@esbuild/darwin-arm64": "0.28.1",
+        "@esbuild/darwin-arm64": "0.28.0",
-        "@esbuild/darwin-x64": "0.28.1",
+        "@esbuild/darwin-x64": "0.28.0",
-        "@esbuild/freebsd-arm64": "0.28.1",
+        "@esbuild/freebsd-arm64": "0.28.0",
-        "@esbuild/freebsd-x64": "0.28.1",
+        "@esbuild/freebsd-x64": "0.28.0",
-        "@esbuild/linux-arm": "0.28.1",
+        "@esbuild/linux-arm": "0.28.0",
-        "@esbuild/linux-arm64": "0.28.1",
+        "@esbuild/linux-arm64": "0.28.0",
-        "@esbuild/linux-ia32": "0.28.1",
+        "@esbuild/linux-ia32": "0.28.0",
-        "@esbuild/linux-loong64": "0.28.1",
+        "@esbuild/linux-loong64": "0.28.0",
-        "@esbuild/linux-mips64el": "0.28.1",
+        "@esbuild/linux-mips64el": "0.28.0",
-        "@esbuild/linux-ppc64": "0.28.1",
+        "@esbuild/linux-ppc64": "0.28.0",
-        "@esbuild/linux-riscv64": "0.28.1",
+        "@esbuild/linux-riscv64": "0.28.0",
-        "@esbuild/linux-s390x": "0.28.1",
+        "@esbuild/linux-s390x": "0.28.0",
-        "@esbuild/linux-x64": "0.28.1",
+        "@esbuild/linux-x64": "0.28.0",
-        "@esbuild/netbsd-arm64": "0.28.1",
+        "@esbuild/netbsd-arm64": "0.28.0",
-        "@esbuild/netbsd-x64": "0.28.1",
+        "@esbuild/netbsd-x64": "0.28.0",
-        "@esbuild/openbsd-arm64": "0.28.1",
+        "@esbuild/openbsd-arm64": "0.28.0",
-        "@esbuild/openbsd-x64": "0.28.1",
+        "@esbuild/openbsd-x64": "0.28.0",
-        "@esbuild/openharmony-arm64": "0.28.1",
+        "@esbuild/openharmony-arm64": "0.28.0",
-        "@esbuild/sunos-x64": "0.28.1",
+        "@esbuild/sunos-x64": "0.28.0",
-        "@esbuild/win32-arm64": "0.28.1",
+        "@esbuild/win32-arm64": "0.28.0",
-        "@esbuild/win32-ia32": "0.28.1",
+        "@esbuild/win32-ia32": "0.28.0",
-        "@esbuild/win32-x64": "0.28.1"
+        "@esbuild/win32-x64": "0.28.0"
       }
     },
     "node_modules/escalade": {

src/browser/services/MouseService.test.ts

@@ -351,96 +351,3 @@ describe('MouseService mouseEventsRequireAlt', () => {
     assert.isFalse(element.classList.contains(MouseEventCssClasses.ENABLE_MOUSE_EVENTS));
   });
 });
-
-describe('MouseService multi-window', () => {
-  interface IRecordingDocument {
-    doc: Document;
-    added: string[];
-    removed: string[];
-    listeners: { [type: string]: EventListener[] };
-  }
-
-  function createRecordingDocument(): IRecordingDocument {
-    const added: string[] = [];
-    const removed: string[] = [];
-    const listeners: { [type: string]: EventListener[] } = {};
-    const doc = {
-      addEventListener: (type: string, listener: EventListener) => {
-        added.push(type);
-        (listeners[type] ??= []).push(listener);
-      },
-      removeEventListener: (type: string) => removed.push(type)
-    } as any;
-    return { doc, added, removed, listeners };
-  }
-
-  it('should manage protocol mouseup/mousemove listeners on the element\'s current document, not the document the terminal was opened with', () => {
-    const mouseStateService = new MouseStateService();
-    const optionsService = new OptionsService({});
-    const mouseService = new MouseService(
-      new MockRenderService(),
-      {
-        getMouseReportCoords: () => ({ col: 0, row: 0, x: 0, y: 0 })
-      } as any,
-      mouseStateService,
-      {
-        triggerDataEvent: () => {},
-        triggerBinaryEvent: () => {},
-        decPrivateModes: { applicationCursorKeys: false }
-      } as any,
-      bufferService,
-      optionsService,
-      new TestSelectionService(),
-      logService,
-      new MockCoreBrowserService()
-    );
-
-    // Simulate a terminal that was opened with one document but whose element now lives in
-    // another document (eg. it was moved to a child window)
-    const openDocument = createRecordingDocument();
-    const childDocument = createRecordingDocument();
-    const elementListeners: { [type: string]: EventListener[] } = {};
-    const element = {
-      classList: {
-        add: () => {},
-        remove: () => {},
-        contains: () => false
-      },
-      addEventListener: (type: string, listener: EventListener) => {
-        (elementListeners[type] ??= []).push(listener);
-      },
-      removeEventListener: () => {},
-      ownerDocument: childDocument.doc
-    } as any;
-
-    mouseService.bindMouse({
-      element,
-      screenElement: createTestMouseTargetElement(),
-      document: openDocument.doc
-    }, disposable => disposable, () => {});
-    mouseStateService.activeProtocol = 'ANY';
-
-    elementListeners['mousedown'][0]({
-      type: 'mousedown',
-      button: 0,
-      buttons: 1,
-      altKey: false,
-      ctrlKey: false,
-      shiftKey: false,
-      preventDefault: () => {}
-    } as any);
-    assert.deepEqual(childDocument.added, ['mouseup', 'mousemove']);
-    assert.deepEqual(openDocument.added, []);
-
-    childDocument.listeners['mouseup'][0]({
-      type: 'mouseup',
-      button: 0,
-      buttons: 0,
-      altKey: false,
-      ctrlKey: false,
-      shiftKey: false
-    } as any);
-    assert.deepEqual(childDocument.removed, ['mouseup', 'mousemove']);
-    assert.deepEqual(openDocument.removed, []);
-  });
-});

src/browser/services/MouseService.ts

@@ -21,7 +21,6 @@ interface IMouseBindContext {
   readonly target: IMouseServiceTarget;
   readonly focus: () => void;
   readonly requestedEvents: RequestedMouseEvents;
-  listenerDocument: Document | null;
 }
 
 export class MouseService implements IMouseService {
@@ -62,7 +61,7 @@ export class MouseService implements IMouseService {
       mousedrag: null,
       mousemove: null
     };
-    const ctx: IMouseBindContext = { target, focus, requestedEvents, listenerDocument: null };
+    const ctx: IMouseBindContext = { target, focus, requestedEvents };
     const eventListeners: Record<'mouseup' | 'wheel' | 'mousedrag' | 'mousemove', EventListener> = {
       mouseup: (ev: Event) => this._handleMouseUp(ctx, ev as MouseEvent),
       wheel: (ev: Event) => this._handleWheel(ctx, ev as WheelEvent),
@@ -88,12 +87,11 @@ export class MouseService implements IMouseService {
 
     // Ensure document-level listeners are removed on dispose
     register(toDisposable(() => {
-      const listenerDocument = ctx.listenerDocument ?? document;
       if (requestedEvents.mouseup) {
-        listenerDocument.removeEventListener('mouseup', requestedEvents.mouseup);
+        document.removeEventListener('mouseup', requestedEvents.mouseup);
       }
       if (requestedEvents.mousedrag) {
-        listenerDocument.removeEventListener('mousemove', requestedEvents.mousedrag);
+        document.removeEventListener('mousemove', requestedEvents.mousedrag);
       }
     }));
 
@@ -201,14 +199,12 @@ export class MouseService implements IMouseService {
     this._sendEvent(ctx, ev);
     if (!ev.buttons) {
       // if no other button is held remove global handlers
-      const listenerDocument = ctx.listenerDocument ?? ctx.target.document;
       if (ctx.requestedEvents.mouseup) {
-        listenerDocument.removeEventListener('mouseup', ctx.requestedEvents.mouseup);
+        ctx.target.document.removeEventListener('mouseup', ctx.requestedEvents.mouseup);
       }
       if (ctx.requestedEvents.mousedrag) {
-        listenerDocument.removeEventListener('mousemove', ctx.requestedEvents.mousedrag);
+        ctx.target.document.removeEventListener('mousemove', ctx.requestedEvents.mousedrag);
       }
-      ctx.listenerDocument = null;
     }
   }
 
@@ -250,15 +246,12 @@ export class MouseService implements IMouseService {
     // of the terminal element.
     // Note: Other emulators also do this for 'mousedown' while a button
     // is held, we currently limit 'mousedown' to the terminal only.
-    // Use the element's current document in case it moved to another window after open.
-    const listenerDocument = ctx.target.element.ownerDocument ?? ctx.target.document;
     if (ctx.requestedEvents.mouseup) {
-      listenerDocument.addEventListener('mouseup', ctx.requestedEvents.mouseup);
+      ctx.target.document.addEventListener('mouseup', ctx.requestedEvents.mouseup);
     }
     if (ctx.requestedEvents.mousedrag) {
-      listenerDocument.addEventListener('mousemove', ctx.requestedEvents.mousedrag);
+      ctx.target.document.addEventListener('mousemove', ctx.requestedEvents.mousedrag);
     }
-    ctx.listenerDocument = listenerDocument;
   }
 
   private _handlePassiveWheel(ctx: IMouseBindContext, ev: WheelEvent): false | void {
@@ -405,9 +398,8 @@ export class MouseService implements IMouseService {
   }
 
   private _handleProtocolChange(ctx: IMouseBindContext, eventListeners: Record<'mouseup' | 'wheel' | 'mousedrag' | 'mousemove', EventListener>, events: CoreMouseEventType): void {
-    const { element } = ctx.target;
+    const { element, document } = ctx.target;
     const { requestedEvents } = ctx;
-    const listenerDocument = ctx.listenerDocument ?? ctx.target.document;
     // apply global changes on events
     if (events) {
       if (this._optionsService.rawOptions.logLevel === 'debug') {
@@ -442,7 +434,7 @@ export class MouseService implements IMouseService {
 
     if (!(events & CoreMouseEventType.UP)) {
       if (requestedEvents.mouseup) {
-        listenerDocument.removeEventListener('mouseup', requestedEvents.mouseup);
+        document.removeEventListener('mouseup', requestedEvents.mouseup);
       }
       requestedEvents.mouseup = null;
     } else {
@@ -451,7 +443,7 @@ export class MouseService implements IMouseService {
 
     if (!(events & CoreMouseEventType.DRAG)) {
       if (requestedEvents.mousedrag) {
-        listenerDocument.removeEventListener('mousemove', requestedEvents.mousedrag);
+        document.removeEventListener('mousemove', requestedEvents.mousedrag);
       }
       requestedEvents.mousedrag = null;
     } else {

src/common/buffer/BufferLine.ts

@@ -71,12 +71,20 @@ export interface IBufferLineStringCache {
  * (if only one particular value is needed) or `loadCell`. For `loadCell` in a loop
  * memory allocs / GC pressure can be greatly reduced by reusing the CellData object.
  */
+/**
+ * Shared empty sparse map for lines with no combining data.
+ * Uses a sentinel + copy-on-write so `copyFrom` can detect empty `_combined` with
+ * reference equality. `_extendedAttrs` uses `undefined` instead (addon-image writes
+ * the map directly without BufferLine APIs).
+ */
+const EMPTY_SPARSE_MAP: {[index: number]: string} = Object.create(null);
+
 export class BufferLine implements IBufferLine {
   protected _data: Uint32Array;
   /** Sparse cache; only read when `IS_COMBINED_MASK` is set in `_data`. */
-  protected _combined: {[index: number]: string} = {};
+  protected _combined: {[index: number]: string} = EMPTY_SPARSE_MAP;
   /** Sparse cache; only read when `HAS_EXTENDED` is set in `_data`. */
-  protected _extendedAttrs: {[index: number]: IExtendedAttrs | undefined} = {};
+  protected _extendedAttrs: {[index: number]: IExtendedAttrs | undefined} | undefined;
   protected _stringCacheEntryRef: WeakRef<IBufferLineStringCacheEntry> | undefined;
   public length: number;
 
@@ -121,6 +129,7 @@ export class BufferLine implements IBufferLine {
     this._invalidateStringCache();
     this._data[index * Constants.CELL_INDICIES + Cell.FG] = value[CHAR_DATA_ATTR_INDEX];
     if (value[CHAR_DATA_CHAR_INDEX].length > 1) {
+      this._ensureCombinedMap();
       this._combined[index] = value[1];
       this._data[index * Constants.CELL_INDICIES + Cell.CONTENT] = index | Content.IS_COMBINED_MASK | (value[CHAR_DATA_WIDTH_INDEX] << Content.WIDTH_SHIFT);
     } else {
@@ -211,7 +220,7 @@ export class BufferLine implements IBufferLine {
       cell.combinedData = '';
     }
     if (cell.bg & BgFlags.HAS_EXTENDED) {
-      cell.extended = this._extendedAttrs[index]!;
+      cell.extended = this._extendedAttrs![index]!;
     } else {
       // Do not mutate cell.extended in place: it may still reference this line's map entry from a
       // prior loadCell into a reused CellData (e.g. $workCell during insert/delete).
@@ -226,10 +235,11 @@ export class BufferLine implements IBufferLine {
   public setCell(index: number, cell: ICellData): void {
     this._invalidateStringCache();
     if (cell.content & Content.IS_COMBINED_MASK) {
+      this._ensureCombinedMap();
       this._combined[index] = cell.combinedData;
     }
     if (cell.bg & BgFlags.HAS_EXTENDED) {
-      this._extendedAttrs[index] = cell.extended;
+      this._ensureExtendedAttrsMap()[index] = cell.extended;
     }
     this._data[index * Constants.CELL_INDICIES + Cell.CONTENT] = cell.content;
     this._data[index * Constants.CELL_INDICIES + Cell.FG] = cell.fg;
@@ -244,7 +254,7 @@ export class BufferLine implements IBufferLine {
   public setCellFromCodepoint(index: number, codePoint: number, width: number, attrs: IAttributeData): void {
     this._invalidateStringCache();
     if (attrs.bg & BgFlags.HAS_EXTENDED) {
-      this._extendedAttrs[index] = attrs.extended;
+      this._ensureExtendedAttrsMap()[index] = attrs.extended;
     }
     this._data[index * Constants.CELL_INDICIES + Cell.CONTENT] = codePoint | (width << Content.WIDTH_SHIFT);
     this._data[index * Constants.CELL_INDICIES + Cell.FG] = attrs.fg;
@@ -262,12 +272,14 @@ export class BufferLine implements IBufferLine {
     let content = this._data[index * Constants.CELL_INDICIES + Cell.CONTENT];
     if (content & Content.IS_COMBINED_MASK) {
       // we already have a combined string, simply add
+      this._ensureCombinedMap();
       this._combined[index] += stringFromCodePoint(codePoint);
     } else {
       if (content & Content.CODEPOINT_MASK) {
         // normal case for combining chars:
         //  - move current leading char + new one into combined string
         //  - set combined flag
+        this._ensureCombinedMap();
         this._combined[index] = stringFromCodePoint(content & Content.CODEPOINT_MASK) + stringFromCodePoint(codePoint);
         content &= ~Content.CODEPOINT_MASK; // set codepoint in buffer to 0
         content |= Content.IS_COMBINED_MASK;
@@ -410,11 +422,13 @@ export class BufferLine implements IBufferLine {
         }
       }
       // remove any cut off extended attributes
-      const extKeys = Object.keys(this._extendedAttrs);
+      if (this._extendedAttrs) {
-      for (let i = 0; i < extKeys.length; i++) {
+        const extKeys = Object.keys(this._extendedAttrs);
-        const key = parseInt(extKeys[i], 10);
+        for (let i = 0; i < extKeys.length; i++) {
-        if (key >= cols) {
+          const key = parseInt(extKeys[i], 10);
-          delete this._extendedAttrs[key];
+          if (key >= cols) {
+            delete this._extendedAttrs[key];
+          }
         }
       }
     }
@@ -450,8 +464,8 @@ export class BufferLine implements IBufferLine {
       }
       return;
     }
-    this._combined = {};
+    this._combined = EMPTY_SPARSE_MAP;
-    this._extendedAttrs = {};
+    this._extendedAttrs = undefined;
     for (let i = 0; i < this.length; ++i) {
       this.setCell(i, fillCellData);
     }
@@ -608,19 +622,57 @@ export class BufferLine implements IBufferLine {
   private _copyCellMapsFrom(src: BufferLine, srcCol: number, destCol: number): void {
     const srcStart = srcCol * Constants.CELL_INDICIES;
     if (src._data[srcStart + Cell.CONTENT] & Content.IS_COMBINED_MASK) {
+      this._ensureCombinedMap();
       this._combined[destCol] = src._combined[srcCol];
     }
     if (src._data[srcStart + Cell.BG] & BgFlags.HAS_EXTENDED) {
-      this._extendedAttrs[destCol] = src._extendedAttrs[srcCol];
+      this._ensureExtendedAttrsMap()[destCol] = src._extendedAttrs![srcCol]!;
     }
   }
 
   /** Rebuild sparse maps from another line, keyed only by `_data` flags. */
   private _copySparseMapsFrom(line: BufferLine): void {
+    const srcCombined = line._combined;
+    const srcExtended = line._extendedAttrs;
+
+    // Fast path: blank / scroll-recycle source (empty `_combined` sentinel, no extended map).
+    if (srcCombined === EMPTY_SPARSE_MAP && !srcExtended) {
+      this._combined = EMPTY_SPARSE_MAP;
+      this._extendedAttrs = undefined;
+      return;
+    }
+    this._copySparseMapsFromDense(line);
+  }
+
+  /** Copy sparse maps by scanning `_data` flags (inlined, no per-cell function calls). */
+  private _copySparseMapsFromDense(line: BufferLine): void {
     this._combined = {};
     this._extendedAttrs = {};
-    for (let i = 0; i < line.length; i++) {
+    const srcData = line._data;
-      this._copyCellMapsFrom(line, i, i);
+    const srcCombined = line._combined;
+    const srcExtended = line._extendedAttrs;
+    const len = line.length;
+    const indices = Constants.CELL_INDICIES;
+    const combined = this._combined;
+    const extendedAttrs = this._extendedAttrs;
+    for (let i = 0; i < len; i++) {
+      const start = i * indices;
+      if (srcData[start + Cell.CONTENT] & Content.IS_COMBINED_MASK) {
+        combined[i] = srcCombined[i];
+      }
+      if (srcData[start + Cell.BG] & BgFlags.HAS_EXTENDED) {
+        extendedAttrs[i] = srcExtended![i];
+      }
     }
   }
+
+  private _ensureCombinedMap(): void {
+    if (this._combined === EMPTY_SPARSE_MAP) {
+      this._combined = {};
+    }
+  }
+
+  private _ensureExtendedAttrsMap(): {[index: number]: IExtendedAttrs | undefined} {
+    return this._extendedAttrs ??= {};
+  }
 }

test/benchmark/BufferLine.benchmark.ts

@@ -0,0 +1,113 @@
+/**
+ * Copyright (c) 2026 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { perfContext, before, RuntimeCase } from 'xterm-benchmark';
+import { BufferLine, DEFAULT_ATTR_DATA } from 'common/buffer/BufferLine';
+import { BufferLineStringCache } from 'common/buffer/BufferLineStringCache';
+import { CellData } from 'common/buffer/CellData';
+import { BgFlags, NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE, UnderlineStyle } from 'common/buffer/Constants';
+
+const ITERATIONS = 500_000;
+const stringCache = new BufferLineStringCache();
+const nullCell = CellData.fromCharData([0, NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE]);
+const yCell = CellData.fromCharData([0, 'y', 1, 'y'.charCodeAt(0)]);
+
+function fillPlainY(line: BufferLine, cols: number): void {
+  for (let i = 0; i < cols; i++) {
+    line.setCellFromCodepoint(i, 'y'.charCodeAt(0), 1, DEFAULT_ATTR_DATA);
+  }
+}
+
+function setupScrollRecyclePair(cols: number): { recycled: BufferLine, blank: BufferLine } {
+  const blank = new BufferLine(stringCache, cols, nullCell, false);
+  const recycled = new BufferLine(stringCache, cols, yCell, false);
+  fillPlainY(recycled, cols);
+  return { recycled, blank };
+}
+
+/** Source line with combining chars and extended attrs spread across columns. */
+function buildSparseSourceLine(cols: number): BufferLine {
+  const line = new BufferLine(stringCache, cols, nullCell, false);
+  for (let i = 0; i < cols; i++) {
+    if (i % 10 === 0) {
+      const cell = CellData.fromCharData([0, 'a', 1, 'a'.charCodeAt(0)]);
+      cell.extended.underlineStyle = UnderlineStyle.CURLY;
+      cell.bg |= BgFlags.HAS_EXTENDED;
+      line.setCell(i, cell);
+    } else if (i % 17 === 0) {
+      line.setCell(i, CellData.fromCharData([1, 'e\u0301', 1, '\u0301'.charCodeAt(0)]));
+    } else {
+      line.setCellFromCodepoint(i, 'y'.charCodeAt(0), 1, DEFAULT_ATTR_DATA);
+    }
+  }
+  return line;
+}
+
+function setupCopyFromSparsePair(cols: number): { dest: BufferLine, src: BufferLine } {
+  const src = buildSparseSourceLine(cols);
+  const dest = new BufferLine(stringCache, cols, yCell, false);
+  fillPlainY(dest, cols);
+  return { dest, src };
+}
+
+perfContext('BufferLine.copyFrom (scroll recycle)', () => {
+  perfContext('cols=80', () => {
+    let recycled: BufferLine;
+    let blank: BufferLine;
+    before(() => {
+      ({ recycled, blank } = setupScrollRecyclePair(80));
+    });
+    new RuntimeCase('', () => {
+      for (let i = 0; i < ITERATIONS; i++) {
+        recycled.copyFrom(blank);
+      }
+      return { payloadSize: ITERATIONS };
+    }, { fork: false }).showAverageRuntime();
+  });
+
+  perfContext('cols=279', () => {
+    let recycled: BufferLine;
+    let blank: BufferLine;
+    before(() => {
+      ({ recycled, blank } = setupScrollRecyclePair(279));
+    });
+    new RuntimeCase('', () => {
+      for (let i = 0; i < ITERATIONS; i++) {
+        recycled.copyFrom(blank);
+      }
+      return { payloadSize: ITERATIONS };
+    }, { fork: false }).showAverageRuntime();
+  });
+});
+
+perfContext('BufferLine.copyFrom (sparse source: combined + extended attrs)', () => {
+  perfContext('cols=80', () => {
+    let dest: BufferLine;
+    let src: BufferLine;
+    before(() => {
+      ({ dest, src } = setupCopyFromSparsePair(80));
+    });
+    new RuntimeCase('', () => {
+      for (let i = 0; i < ITERATIONS; i++) {
+        dest.copyFrom(src);
+      }
+      return { payloadSize: ITERATIONS };
+    }, { fork: false }).showAverageRuntime();
+  });
+
+  perfContext('cols=279', () => {
+    let dest: BufferLine;
+    let src: BufferLine;
+    before(() => {
+      ({ dest, src } = setupCopyFromSparsePair(279));
+    });
+    new RuntimeCase('', () => {
+      for (let i = 0; i < ITERATIONS; i++) {
+        dest.copyFrom(src);
+      }
+      return { payloadSize: ITERATIONS };
+    }, { fork: false }).showAverageRuntime();
+  });
+});