docs: troubleshooting names the stacked-retarget carry refusals

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

docs/troubleshooting.md

@@ -4698,14 +4698,18 @@ to HEAD: the PR body has no valid receipt, the working tree has uncommitted or
 untracked changes (a carry certifies a commit, never a tree that differs from
 it), the receipt's head left HEAD's history and the receipt records no tree to
 compare (a receipt written before `head_tree`, whose head is not in this
-clone), or git could not compare the two product diffs or read the working
-tree's status. The receipt in the body is unchanged and still names the old
-head, so `gstack-ship-queue ready` refuses `QUEUE_RECEIPT_STALE`.
+clone), the PR was retargeted to the base after its stack parent landed but
+the receipt records no `product_patch_id` and `origin/<parent>` no longer
+resolves, so the reviewed range cannot be recomputed, or git could not
+compare the two product diffs or read the working tree's status. The receipt
+in the body is unchanged and still names the old head, so
+`gstack-ship-queue ready` refuses `QUEUE_RECEIPT_STALE`.
 
 **Fix.** Commit or stash every working-tree change, then rerun
 `gstack-ship-receipt carry --pr <n>` at the new head. When the history is
 already rewritten and the receipt predates `head_tree`, run /ship on the new
-head; next time merge the base in instead of rebasing.
+head; next time merge the base in instead of rebasing. For a retargeted stacked
+PR whose older receipt lost its parent branch, run /ship on the new head.
 
 <a id="receipt-carry-tree-mismatch"></a>
 ### `RECEIPT_CARRY_TREE_MISMATCH`
@@ -4734,12 +4738,14 @@ 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
-receipt is not carried. The refusal names the changed product paths.
+receipt is not carried. The refusal names the changed product paths, or for a
+retargeted stacked PR the parent branch and the base.
 
 **Fix.** Run /ship on the new head. The receipt carries only across a
 conflict-only base merge, a test-only change, release metadata, a registered
-output the pregate's regen check proved, or a rebase onto a covered tree with
-the recorded product diff, which the
+output the pregate's regen check proved, a rebase onto a covered tree with
+the recorded product diff, or a stacked PR's retarget once its parent fully
+landed on the base, which the
 `carry` object in the carried receipt records with the product patch-id and
 the range-diff evidence ([unattended.md](unattended.md#the-terminal-line)).