diff --git a/apps/ai-game-creator-shell/src/styles.css b/apps/ai-game-creator-shell/src/styles.css
index d2de3cd8b..89cdff927 100644
--- a/apps/ai-game-creator-shell/src/styles.css
+++ b/apps/ai-game-creator-shell/src/styles.css
@@ -11526,14 +11526,15 @@ button.design-workspace-tree__entry:hover,
 .project-chat-composer-strength-range::-webkit-slider-runnable-track {
   height: 6px;
   border-radius: 999px;
-  /* 已选段一直铺到圆钮右缘（`--strength-ratio` 是无单位档位比例，20px = 圆钮直径），
-     圆钮右缘之外才是未选段；`calc` 让两端在任意轨道宽度下都对齐。 */
+  /* 已选段终点 = **圆钮中心**（`--strength-ratio` 是无单位档位比例；圆钮中心 =
+     10px + ratio * (100% - 20px)，两端各留一个圆钮半径）。原先终点写成 20px + …（= 圆钮
+     **右缘**），亚像素 / 圆角 / 描边一有误差就在圆钮右侧露出一小截橙色。 */
   background: linear-gradient(
     to right,
     var(--platform-accent) 0
-      calc(20px + var(--strength-ratio, 0) * (100% - 20px)),
+      calc(10px + var(--strength-ratio, 0) * (100% - 20px)),
     var(--platform-subpanel-border)
-      calc(20px + var(--strength-ratio, 0) * (100% - 20px)) 100%
+      calc(10px + var(--strength-ratio, 0) * (100% - 20px)) 100%
   );
 }
 
diff --git a/apps/ai-game-creator-shell/tests/chatDialogFrameLayout.test.ts b/apps/ai-game-creator-shell/tests/chatDialogFrameLayout.test.ts
index 0879bb33e..5b9f2d2f6 100644
--- a/apps/ai-game-creator-shell/tests/chatDialogFrameLayout.test.ts
+++ b/apps/ai-game-creator-shell/tests/chatDialogFrameLayout.test.ts
@@ -429,6 +429,19 @@ describe('陶泥儿对话区：Codex 三段式（顶栏 / 唯一滚动区 / 文
     expect(sectionPadding.right).toBe(0);
     expect(sectionPadding.top).toBe(4);
     expect(sectionPadding.bottom).toBe(2);
+
+    // 已选段终点必须与**圆钮中心**重合（`10px + ratio * (100% - 20px)`）：写成 `20px + …`
+    // （= 圆钮**右缘**）时圆钮右侧会露出一小截橙色（4× 设备像素实拍对照见 PR）。
+    const track = desktopDeclarations(
+      `${STRENGTH_RANGE}::-webkit-slider-runnable-track`,
+    );
+    const trackBackground = declaration(track, 'background');
+    expect(trackBackground).toContain(
+      'calc(10px + var(--strength-ratio, 0) * (100% - 20px))',
+    );
+    expect(trackBackground).not.toContain(
+      'calc(20px + var(--strength-ratio, 0) * (100% - 20px))',
+    );
   });
 
   it('窄屏（390px）输入盒仍在文档流、四周有边距，列表底部没有留白', () => {