docs: troubleshooting names the base-written stacked carry (Step 14.5 audit, GST-1199)

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

docs/troubleshooting.md

@@ -5981,7 +5981,10 @@ the reviewed tree but the base moved under it, so the diff a reviewer would see
 is not the reviewed one. For a stacked PR retargeted to the base after its
 parent landed, it means HEAD's product diff against the base is not the range
 reviewed against the parent branch: the parent has not fully landed, or the
-branch changed since. The reviewed verdict does not cover HEAD, so the
+branch changed since. A stacked PR whose receipt was written against the base
+carries from the newest reviewed commit the base already holds
+([ship-policy.md](ship-policy.md#receipt-carry)); it refuses here only when no
+such commit exists or the branch changed since. The reviewed verdict does not cover HEAD, so the
 receipt is not carried. The refusal names the changed product paths, or for a
 retargeted stacked PR the parent branch and the base.