test(tui): lock dunder markdown rendering (#95211)

* test(tui): lock dunder markdown rendering

Co-authored-by: 张贵萍0668001030 <zhang.guiping@xydigit.com>

* test(tui): lock dunder markdown rendering

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/tui/components/hyperlink-markdown.test.ts

@@ -0,0 +1,37 @@
+import { visibleWidth } from "@earendil-works/pi-tui";
+import { describe, expect, it } from "vitest";
+import { normalizeTestText } from "../../../test/helpers/normalize-text.js";
+import { markdownTheme } from "../theme/theme.js";
+import { HyperlinkMarkdown } from "./hyperlink-markdown.js";
+
+describe("HyperlinkMarkdown", () => {
+  it("moves dunder identifiers intact across fenced code wrap boundaries", () => {
+    const markdown = new HyperlinkMarkdown(
+      ["```python", 'if __name__ == "__main__":', "```"].join("\n"),
+      0,
+      0,
+      markdownTheme,
+    );
+
+    const rendered = markdown.render(12);
+    const normalized = rendered.map((line) => normalizeTestText(line));
+
+    expect(rendered.every((line) => visibleWidth(line) <= 12)).toBe(true);
+    expect(normalized.some((line) => line.includes("__name__ =="))).toBe(true);
+    expect(normalized.some((line) => line.includes('"__main__":'))).toBe(true);
+  });
+
+  it("preserves underscores in fenced and inline code", () => {
+    const markdown = new HyperlinkMarkdown(
+      ["```python", "is_palindrome", "```", "", "Call `__init__`."].join("\n"),
+      0,
+      0,
+      markdownTheme,
+    );
+
+    const normalized = markdown.render(16).map((line) => normalizeTestText(line));
+
+    expect(normalized.some((line) => line.includes("is_palindrome"))).toBe(true);
+    expect(normalized.some((line) => line.includes("__init__"))).toBe(true);
+  });
+});