fix(web): keep external link labels breakable

Review follow-up on the #8807 port. Routing agent images through the expanded
preview wrapped an anchor's children in MarkdownLinkContext, which made
MarkdownExternalLinkContent's first child an element rather than the leading
text string it splits with <wbr/>. External links mixing leading text with
inline formatting rendered their whole label as one whitespace-nowrap run and
overflowed the chat column. The provider now wraps the result instead of the
children. The defect is upstream's too.

Author: rynfar

apps/web/src/components/ChatMarkdown.test.tsx

@@ -332,4 +332,14 @@ describe("ChatMarkdown Windows file links", () => {
     expect(html).not.toContain("d:alert");
     expect(html).not.toContain("chat-markdown-file-link");
   });
+
+  it("keeps external link labels breakable when they mix text and formatting", () => {
+    const markup = renderToStaticMarkup(
+      <ChatMarkdown text="[a very long external link label that should wrap **bold**](https://example.com/x)" />,
+    );
+
+    // The leading text is split with <wbr/> so a long label wraps inside the
+    // chat column instead of overflowing it.
+    expect(markup).toContain("<wbr");
+  });
 });

apps/web/src/components/ChatMarkdown.tsx

@@ -2229,9 +2229,15 @@ function ChatMarkdown({
               }}
             >
               {faviconHost && hastHasText(node) ? (
-                <MarkdownExternalLinkContent host={faviconHost} plainText={plainHastText(node)}>
-                  {linkChildren}
-                </MarkdownExternalLinkContent>
+                // The provider wraps the result rather than the children:
+                // MarkdownExternalLinkContent inspects its first child for the
+                // leading text it splits with <wbr/>, and an element there
+                // makes the whole label one unbreakable run.
+                <MarkdownLinkContext value>
+                  <MarkdownExternalLinkContent host={faviconHost} plainText={plainHastText(node)}>
+                    {children}
+                  </MarkdownExternalLinkContent>
+                </MarkdownLinkContext>
               ) : (
                 linkChildren
               )}