diff --git a/ui/src/components/MarkdownBody.test.tsx b/ui/src/components/MarkdownBody.test.tsx
index bdcfd28393b..1a6d8b8fcf2 100644
--- a/ui/src/components/MarkdownBody.test.tsx
+++ b/ui/src/components/MarkdownBody.test.tsx
@@ -241,6 +241,32 @@ describe("MarkdownBody", () => {
     expect(html).not.toContain("paperclip-mention-chip--issue");
   });
 
+  it("holds the quicklook preview until an issue mention is confirmed readable (PAP-16070)", () => {
+    // While the fetch is in flight we don't know if the viewer can read the
+    // issue. The mention stays a clickable link, but the IssueLinkQuicklook
+    // hover preview (a Radix Popover portal) must NOT mount yet: a private
+    // mention 404s straight to the locked chip, and mounting then tearing down
+    // that portal to swap in the chip is the element churn that crashed the
+    // chat transcript renderer.
+    const html = renderMarkdown("Depends on PAP-1271 for the hover state.");
+
+    expect(html).toContain('data-mention-pending="true"');
+    expect(html).toContain('data-mention-kind="issue"');
+    expect(html).toContain("paperclip-markdown-issue-ref");
+    // Clickability is preserved through the loading state.
+    expect(html).toContain('href="/issues/PAP-1271"');
+    expect(html).toContain(">PAP-1271<");
+  });
+
+  it("drops the pending marker once a seeded (readable) issue mention resolves", () => {
+    const html = renderMarkdown("Depends on PAP-1271 for the hover state.", [
+      { identifier: "PAP-1271", status: "done" },
+    ]);
+
+    expect(html).toContain('href="/issues/PAP-1271"');
+    expect(html).not.toContain('data-mention-pending="true"');
+  });
+
   it("uses concise issue aria labels until a distinct title is available", () => {
     const html = renderMarkdown("Depends on PAP-1271 and PAP-1272.", [
       { identifier: "PAP-1271", status: "done" },
diff --git a/ui/src/components/MarkdownBody.tsx b/ui/src/components/MarkdownBody.tsx
index e7e6cecf5e4..56543006a2b 100644
--- a/ui/src/components/MarkdownBody.tsx
+++ b/ui/src/components/MarkdownBody.tsx
@@ -119,10 +119,25 @@ function MarkdownIssueLink({
   const status = data?.status;
   const issueLabel = title !== identifier ? `Issue ${identifier}: ${title}` : `Issue ${identifier}`;
 
+  // Until the fetch settles we don't yet know whether this viewer can read the
+  // issue. Keep the mention a plain link (clickable, styled as today) but hold
+  // off mounting the IssueLinkQuicklook hover preview — a Radix Popover portal —
+  // until `data` confirms the issue is readable.
+  //   - Correctness (PAP-16070): a private mention 404s straight to the locked
+  //     chip. Mounting the quicklook popover during the loading `<Link>` only to
+  //     tear the portal down and swap in a plain `<span>` chip on the 404 is the
+  //     element churn that crashed the chat transcript's primary renderer (it
+  //     fell through to the safe fallback). Loading link → chip stays portal-free.
+  //   - Privacy: don't prefetch / hover-preview an issue of unconfirmed
+  //     readability. `data-mention-pending` marks the transient state for tests.
+  const pending = !data;
+
   return (
     <Link
       to={`/issues/${identifier}`}
       data-mention-kind="issue"
+      disableIssueQuicklook={pending}
+      data-mention-pending={pending ? "true" : undefined}
       // Boxless inline mention: the unified status glyph + a regular-weight
       // underlined link, optically centered with the body text.
       className={cn("paperclip-markdown-issue-ref", "font-normal underline")}