train S1: merge #3892 at 13601c0440 v1.94.16.0

docs/ship-policy.md

@@ -53,6 +53,7 @@ refuses the file (`POLICY_GSTACK_TOO_OLD`). `validate` ends with
 | `maintainers` | GitHub logins | `[]` | Maintainer set for `/review` contributor mode; empty means repository push permission. |
 | `stamp_files` | globs | `[]` | The repo's stamp rule: when set, only these files may differ by a stamp (list the version file, manifests, plugin trees and the files holding the PR's own `since:` rows). It applies before every other stamp rule, so a doc `vX` mention outside it is a difference. |
 | `stamp_patterns` | literal templates | `[]` | At most 16 templates of at most 128 characters, each with exactly one `{version}` slot (`"version": "{version}"`, `since: '{version}'`, `<!-- x-stamp: {version} -->`); matched literally at a version boundary, never as a regex. The restamp writer, its mention scanner and the tree receipt use them beside the built-in forms. |
+| `stamp_placeholders` | literal placeholders | `[]` | At most 16 one-line literals of at most 32 characters, never `{version}` and never a version (`["TBD"]`). On a line the branch added itself, a placeholder inside a `stamp_patterns` template (`since: 'TBD'` under `since: '{version}'`) may become that template at the new version, and finish's route, the receipt carry and the tree receipt read the change as a stamp. The built-in forms never take a placeholder, and neither does a base line, even one whose text duplicates a branch line. The writer does not fill placeholders: the repo's `restamp_command` does. A newer key: set `min_gstack_version` to the release `gstack-ship-policy validate` names. Empty accepts no placeholder. |
 | `restamp_command` | command or `null` | `null` | The repo's own restamp, run first in the staging worktree; see [restamp_command](#restamp-command). |
 | `migrations` | `{ dir, id }` or `null` | `null` | The migration directory and a regex with exactly one capture group for the number in a file name (`"^v(\\d+)-"`); `gstack-pregate regate` reports `MIGRATION_COLLISION`. |
 | `gate_command` | command or `null` | `null` | The repo's full pre-merge gate. `gstack-ship-queue gate-ahead` and `ready` print it for the caller to run (in the background or in CI); gstack never executes it. Needs `min_gstack_version`. |