fix(ship): finish takes a landed stack parent as the reviewed base, fail-closed on metadata and never bounded (GST-1399)

Ported from #4013 onto #4020's route: the stacked-parent path judges every
shipped path's metadata class against main, counts stamp_paths and
release_outputs only while stamp-only, and never feeds the bounded route.
The receipt carry's landed-parent search finds a squash main edited since.

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

docs/ship-policy.md

@@ -1685,7 +1685,37 @@ child made before its receipt brought it in) unless HEAD changed it against the
 base (GST-1214): an equal
 patch-id carries with reason `stack parent <sha12> landed`, base context next
 to the child's unchanged hunks is `RECEIPT_CARRY_SCOPED_REVIEW`, and any other
-difference refuses with `RECEIPT_CARRY_PRODUCT_CHANGED`.
+difference refuses with `RECEIPT_CARRY_PRODUCT_CHANGED`. When merging the commit
+into the current base conflicts because the base edited the landed lines
+afterwards, the base commits since the fork that touched every path of its
+change are tried newest first (at most 200), so the squash itself still counts
+(GST-1399).
+
+**finish after a stack parent lands (GST-1399).** A child reviewed against its
+parent branch passes the parent's head to `gstack-ship-release finish
+--reviewed-base`, even after the parent squash-merged and the child merged the
+base. finish takes it when the branch contains it and a base commit holds its
+change outside release metadata and changelog fragments (a release folds every
+fragment on the base), found as the carry finds a landed parent, and
+prints `REVIEWED_BASE: stack parent <sha12> landed on origin/<base> at <sha12>`.
+The route, a granted fix-check's sides, the scoped-review packet and the docs
+carry then compare each commit's patch from that parent, so the parent's and the
+base's edits route as `base=`. The route also reads every path the branch ships
+against the base, changed since review or not, and judges every shipped path's
+release-metadata class against the base, so a parent change the base never
+received (a `package.json` script, even after the child's version bump) or a
+merge that kept a line the base changed since still stops. Both the landed check
+and this class count a `stamp_paths` or `release_outputs` file as metadata only
+while its edit is a version stamp, as `stamp_files` are; any other edit to one
+must be held by the base or stop. A landed stack parent never takes the bounded
+route: a post-review edit that a child reviewed against the base would send to
+one scoped reader stops for Steps 5–11.5 instead. A path the child no longer changes against the base routes as base only
+when the base already holds the reviewed change to it (a three-way merge of the
+reviewed change into the base leaves the base's bytes, and a reviewed mode change
+is the base's mode); a post-review revert to the base's content or mode still
+stops. Any other commit
+off the base, a parent the base never received included, stops with
+`--reviewed-base <sha> is not on origin/<base>, nor a landed stack parent`.
 
 Since the release that added `review_scope`. A `/ship` receipt names the head it
 reviewed, so a conflict-only merge of the base or a test-only fix used to