diff --git a/platform/platform-tests/testSrc/com/intellij/openapi/editor/impl/EditorCharacterGridSizeTest.java b/platform/platform-tests/testSrc/com/intellij/openapi/editor/impl/EditorCharacterGridSizeTest.java
new file mode 100644
index 000000000000..161352614f91
--- /dev/null
+++ b/platform/platform-tests/testSrc/com/intellij/openapi/editor/impl/EditorCharacterGridSizeTest.java
@@ -0,0 +1,40 @@
+// Copyright 2000-2026 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.openapi.editor.impl;
+
+import com.intellij.openapi.editor.ex.EditorEx;
+
+public class EditorCharacterGridSizeTest extends AbstractEditorTest {
+  private static final String LONG_LINE = "x".repeat(200);
+  private static final int CONTENT_WIDTH = LONG_LINE.length() * TEST_CHAR_WIDTH;
+
+  private void enableGridMode() {
+    getEditor().getSettings().setCharacterGridWidthMultiplier(1.0f);
+    ((EditorEx)getEditor()).reinitSettings();
+    assertNotNull(((EditorImpl)getEditor()).getCharacterGrid());
+  }
+
+  private int preferredWidth() {
+    return getEditor().getContentComponent().getPreferredSize().width;
+  }
+
+  // IJPL-247496: non-wrapping grid editors (Markdown) must expose the full line width, not the viewport.
+  public void testNonWrappingGridEditorIsScrollableToTheEndOfLongLines() {
+    initText(LONG_LINE);
+    getEditor().getSettings().setAdditionalColumnsCount(0);
+    setEditorVisibleSize(20, 10);
+    enableGridMode();
+
+    assertTrue(getEditor().getScrollingModel().getVisibleArea().width < CONTENT_WIDTH);
+    assertTrue("preferred=" + preferredWidth(), preferredWidth() >= CONTENT_WIDTH);
+  }
+
+  // IJPL-180831: soft-wrapping grid editors (terminal) still clamp preferred width to the viewport.
+  public void testWrappingGridEditorStaysClampedToViewport() {
+    initText(LONG_LINE);
+    getEditor().getSettings().setAdditionalColumnsCount(0);
+    configureSoftWraps(20);
+    enableGridMode();
+
+    assertTrue("preferred=" + preferredWidth(), preferredWidth() < CONTENT_WIDTH);
+  }
+}