docs(pregate, ship-policy): the fragment fold's two receipt rules, and clear applies them too

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

docs/pregate.md

@@ -447,7 +447,8 @@ receipt for H when the two trees differ only as a stamp does:
   stamps, each hunk in them must be the exact old → new rewrite under
   `stamp_patterns` (literal `{version}` templates) or the built-in forms
   (`(was X)`, `since: X`, `vX`), and the version file, `package.json`'s
-  `version`, a lockfile's root version keys and a CHANGELOG re-heading have
+  `version`, a lockfile's root version keys and a CHANGELOG re-heading (under
+  `changelog_fragments`, also the fold of the fragments the head deletes) have
   their own built-in rules. There is no second list and no looser rule here:
   the file verdicts `clear` reaches on a pair are the verdicts
   `gstack-tree-receipt --gated G --current H` reaches, and its gate rule holds
@@ -466,7 +467,9 @@ receipt for H when the two trees differ only as a stamp does:
   the policy label (`origin/<base>@<sha>:.gstack/ship-policy.json`) and every
   differing path with the rule that classed it (`version-file`,
   `version-manifest`, `manifest-version`, `lockfile-root-version`,
-  `changelog-heading`, `stamp_files`, `stamp_paths`, `release_outputs`). `clear` prints the same
+  `changelog-heading`, `changelog-fragments` for the CHANGELOG under the fold,
+  `changelog_fragments` for a folded fragment's deletion, `stamp_files`,
+  `stamp_paths`, `release_outputs`). `clear` prints the same
   as `PREGATE_RECEIPT_SUBSTITUTED: …`, `verify` repeats it on its ok line, and
   the ship receipt carries the receipt string. The receipt's own tests and
   failed checks apply as before (its exit status is checked only when

docs/ship-policy.md

@@ -1198,10 +1198,12 @@ writes no version in Step 12 and writes Step 13's entry as
 **The fold.** `gstack-restamp` (and so `land`) concatenates the fragment
 bodies in path order above any legacy `[Unreleased]` section, re-heads both as
 one `## [<version>] - <date>` section at the top, and deletes the fragment
-files, in one stamp. The tree receipt's `changelog-fragments` rule calls a
-deleted fragment a stamp only when its body appears verbatim, in order, among
-the lines added under the new heading; an edited fold, or a fragment deleted
-without its text, is a change.
+files, in one stamp. The tree receipt, and so `gstack-pregate clear`'s
+stamp-only substitution, calls a deleted fragment a stamp (rule
+`changelog_fragments`) only when the new CHANGELOG section is exactly the
+deleted fragments' bodies in path order above any legacy `[Unreleased]` text
+(rule `changelog-fragments`); an edited fold, or a fragment deleted without
+its text, is a change.
 
 **Version Gate.** The workflow runs on every PR (no path filter), so a PR
 that touches no release file still has to prove its entry. Under the key, an