Fix teleport issue when coming back from alt buffer

src/common/TestUtils.test.ts

@@ -46,6 +46,9 @@ export class MockBufferService implements IBufferService {
   public scrollLines(disp: number, suppressScrollEvent?: boolean): void {
     throw new Error('Method not implemented.');
   }
+  public syncScrollPosition(): void {
+    // Mock implementation - no-op for tests
+  }
   public resize(cols: number, rows: number): void {
     this.cols = cols;
     this.rows = rows;

src/common/buffer/BufferSet.ts

@@ -91,6 +91,8 @@ export class BufferSet extends Disposable implements IBufferSet {
       activeBuffer: this._normal,
       inactiveBuffer: this._alt
     });
+    // Prevent scrollbar "teleport" to top of the terminal, from previous alt buffer.
+    this._bufferService.syncScrollPosition();
   }
 
   /**

src/common/services/BufferService.ts

@@ -148,4 +148,11 @@ export class BufferService extends Disposable implements IBufferService {
       this._onScroll.fire(buffer.ydisp);
     }
   }
+
+  /**
+   * Synchronize the scroll position by firing a scroll event with the current buffer's ydisp.
+   */
+  public syncScrollPosition(): void {
+    this._onScroll.fire(this.buffer.ydisp);
+  }
 }

src/common/services/Services.ts

@@ -22,6 +22,7 @@ export interface IBufferService {
   onScroll: Event<number>;
   scroll(eraseAttr: IAttributeData, isWrapped?: boolean): void;
   scrollLines(disp: number, suppressScrollEvent?: boolean): void;
+  syncScrollPosition(): void;
   resize(cols: number, rows: number): void;
   reset(): void;
 }