修复评审器跨组件修改项跳转丢失并展开完整文档视图

- DiffView 聚焦 effect 依赖补上 before/after：stage 文本到达、
  MergeView 重建后重新应用选区和滚动，跨组件点击不再停在顶部；
- 非可编辑面板加 drawSelection，聚焦范围在浏览器中可见；
- 移除 collapseUnchanged，评审始终可读完整未改动段落；
- 滚动容器移到 .cm-mergeView 外层，编辑器高度自适应内容；
- 新增 3 项 Vitest 覆盖折叠移除与聚焦时序，共 9 项通过；
- README 与 explanation 同步当前检查数量。

reviewer/tests/DiffView.test.tsx

@@ -1,8 +1,22 @@
 import { render, screen } from "@testing-library/react";
 import { describe, expect, it } from "vitest";
+import { EditorView } from "@codemirror/view";
 
 import { DiffView } from "../src/client/DiffView.js";
 
+function leftPaneSelection(): { from: number; to: number } | null {
+  const pane = document.querySelector(".diff-host .cm-editor");
+  if (pane === null) {
+    return null;
+  }
+  const view = EditorView.findFromDOM(pane as HTMLElement);
+  if (view === null) {
+    return null;
+  }
+  const { from, to } = view.state.selection.main;
+  return { from, to };
+}
+
 describe("DiffView", () => {
   it("keeps Markdown and raw HTML as inert editor text", () => {
     render(
@@ -18,4 +32,68 @@ describe("DiffView", () => {
     expect(document.querySelector("img")).toBeNull();
     expect(document.querySelector("script")).toBeNull();
   });
+
+  it("keeps long unchanged sections available in the full document view", () => {
+    const before = Array.from({ length: 30 }, (_, index) => `line ${index + 1}`);
+    const after = [...before];
+    after[14] = "changed line 15";
+
+    render(
+      <DiffView
+        before={before.join("\n")}
+        after={after.join("\n")}
+        beforeLabel="清洗前"
+        afterLabel="清洗后"
+      />,
+    );
+
+    expect(document.querySelector(".cm-collapsedLines")).toBeNull();
+  });
+
+  it("re-applies the focus selection after the compared texts change", () => {
+    const longText = (mark: string) =>
+      Array.from({ length: 30 }, (_, index) => (index === 14 ? mark : `line ${index + 1}`)).join("\n");
+
+    const { rerender } = render(
+      <DiffView before={longText("old")} after={longText("new")} beforeLabel="清洗前" afterLabel="清洗后" />,
+    );
+
+    // 模拟点击跨组件修改项：focusRange 先落在旧文本上，stage 文本随后到达。
+    rerender(
+      <DiffView
+        before={longText("old")}
+        after={longText("new")}
+        beforeLabel="组件 1 执行前"
+        afterLabel="组件 1 执行后"
+        focusRange={{ start: 58, end: 61 }}
+      />,
+    );
+    rerender(
+      <DiffView
+        before={longText("stage before")}
+        after={longText("stage after")}
+        beforeLabel="组件 2 执行前"
+        afterLabel="组件 2 执行后"
+        focusRange={{ start: 58, end: 71 }}
+      />,
+    );
+
+    // 最终视图必须是组件 2 的文本，且选区重新落在新文本的目标范围上。
+    expect(screen.getByRole("region", { name: "组件 2 执行前与组件 2 执行后对比" })).toBeInTheDocument();
+    expect(leftPaneSelection()).toEqual({ from: 58, to: 71 });
+  });
+
+  it("applies the focus selection when it arrives with the initial texts", () => {
+    render(
+      <DiffView
+        before={"a\nb"}
+        after={"a\nc"}
+        beforeLabel="清洗前"
+        afterLabel="清洗后"
+        focusRange={{ start: 0, end: 1 }}
+      />,
+    );
+
+    expect(leftPaneSelection()).toEqual({ from: 0, to: 1 });
+  });
 });