fix(webview): mask reference link definitions before mention rewriting

Address CodeRabbit finding on #1257:

- Add definition to MENTION_MASK_NODE_TYPES so a reference link destination (e.g. [docs]: @/docs/readme.md) is masked before prepareMentions() runs. Without it, the destination was rewritten to a mention placeholder and that placeholder became the reference link's href, corrupting the href with control characters instead of rendering a mention span.

- Regression test: the reference link keeps its original href, the destination never becomes a mention span, a real mention in the body stays actionable, and no placeholder control characters leak into the output.

Author: easonliang28

webview-ui/src/components/common/MarkdownBlock.tsx

@@ -26,9 +26,20 @@ const MENTION_PLACEHOLDER_CHAR = "\u0001"
 const MENTION_PLACEHOLDER_REGEX = new RegExp(`${MENTION_PLACEHOLDER_CHAR}(\\d+)${MENTION_PLACEHOLDER_CHAR}`, "g")
 
 // mdast node types whose raw source regions must never be mention-rewritten:
-// code blocks (fenced or indented), inline code, links, images, raw HTML, and
-// math all render as literal or non-text content.
-const MENTION_MASK_NODE_TYPES = new Set(["code", "inlineCode", "link", "image", "html", "inlineMath", "math"])
+// code blocks (fenced or indented), inline code, links, images, raw HTML, math,
+// and reference link definitions all render as literal or non-text content
+// (rewriting a definition's destination would corrupt the reference link's
+// href instead of producing a mention span).
+const MENTION_MASK_NODE_TYPES = new Set([
+	"code",
+	"inlineCode",
+	"link",
+	"image",
+	"html",
+	"inlineMath",
+	"math",
+	"definition",
+])
 
 /**
  * Rewrite mention patterns in the RAW markdown string before remark tokenizes
@@ -44,10 +55,10 @@ const MENTION_MASK_NODE_TYPES = new Set(["code", "inlineCode", "link", "image",
  * Matching runs on the raw string so the shared regex's boundary rules apply
  * unchanged (replacing literal regions with spaces would turn a preceding `)`
  * or backtick into whitespace and make non-mentions actionable). Literal / non-
- * text regions (code, links, images, HTML, math) are marked via a throwaway
- * mdast parse with the exact positions remark sees, and a match whose range
- * intersects one of them is discarded so mentions inside such regions stay
- * inert.
+ * text regions (code, links, images, HTML, math, reference link definitions)
+ * are marked via a throwaway mdast parse with the exact positions remark sees,
+ * and a match whose range intersects one of them is discarded so mentions
+ * inside such regions stay inert.
  */
 function prepareMentions(markdown: string): { preparedMarkdown: string; mentions: string[] } {
 	if (!markdown) {
@@ -58,8 +69,9 @@ function prepareMentions(markdown: string): { preparedMarkdown: string; mentions
 	// reported positions match what remark will tokenize. Mark literal and
 	// non-text regions (mdast positions carry absolute source offsets): a
 	// mention inside any of them must stay inert, because code and links render
-	// as literal/interactive content, and images, raw HTML, and math keep their
-	// source text unchanged.
+	// as literal/interactive content, images, raw HTML, and math keep their
+	// source text unchanged, and a reference link definition's destination
+	// becomes the link's href (rewriting it would corrupt the href).
 	const tree = unified().use(remarkParse).use(remarkGfm).use(remarkMath).parse(markdown)
 
 	const isMasked = new Array<boolean>(markdown.length).fill(false)

webview-ui/src/components/common/__tests__/MarkdownBlock.spec.tsx

@@ -358,6 +358,33 @@ describe("MarkdownBlock", () => {
 			expect(mockPostMessage).not.toHaveBeenCalledWith(expect.objectContaining({ type: "openMention" }))
 		})
 
+		it("keeps reference link destinations inert and preserves the original href", async () => {
+			// A reference definition's destination renders as the reference link's
+			// href, so rewriting it to a mention placeholder would corrupt the href
+			// (control characters instead of the original path) rather than produce
+			// a mention span. The whole definition region must stay masked.
+			const markdown = "[docs]: @/docs/readme.md\n\nSee [docs] and @problems."
+			const { container } = render(<MarkdownBlock markdown={markdown} mentions />)
+
+			await screen.findByText(/See/, { exact: false })
+
+			// The reference link keeps its original href, untouched by mention
+			// preprocessing, and the destination never becomes a mention span.
+			const anchor = container.querySelector("a")!
+			expect(anchor).toHaveAttribute("href", "@/docs/readme.md")
+			expect(anchor.textContent).toBe("docs")
+			expect(container.querySelectorAll("a span.mention-context-highlight").length).toBe(0)
+
+			// Masking the definition must not affect a real mention in the body.
+			const mentions = container.querySelectorAll("span.mention-context-highlight")
+			expect(mentions.length).toBe(1)
+			expect(mentions[0].textContent).toBe("@problems")
+
+			// No placeholder control characters leak into the rendered output.
+			expect(container.textContent).not.toContain("\u0001")
+			expect(anchor.getAttribute("href")).not.toContain("\u0001")
+		})
+
 		it("keeps the shared regex boundary rules when a mention directly follows a link or inline code", async () => {
 			// Matching must run on the raw string so the shared regex's start boundary
 			// sees the real characters: with no whitespace after a closing `)` or a