docs: define traceable availability markers

docs/CONSUMERS.md

@@ -113,12 +113,17 @@ the machinery at all:
    self-hosted runner still wants it: the guard's value is the day
    somebody adds one.
 
-   This guide documents `main`. New machinery is marked **unreleased**
+   This guide documents `main`. New machinery is marked with the lowercase
-   here until a release tag ships it — and the release PR that ships the
+   word `unreleased` in bold, immediately followed by its issue citation
-   machinery clears, in that same PR, every marker its own assembled
+   (for example, `(#238)`); whitespace between them may include a line break.
-   section makes false: the section cites its issues, each marker cites
+   A citation is mandatory, because a marker the guard cannot trace is a
-   the same issue, and the release PR's diff is the one place both
+   marker it cannot prove false. Cross-repo citations such as `(crew#293)`
-   halves are visible at once (#221). If an action does not exist at the
+   satisfy that traceability rule but are not compared with this repository's
+   release section. The ceremony-only `marker-check.sh` guard enforces both
+   rules. The release PR that ships the machinery clears, in that same PR,
+   every marker its own assembled section makes false: the section cites its
+   issues, each marker cites the same issue, and the release PR's diff is the
+   one place both halves are visible at once (#221). If an action does not exist at the
    consumer's pinned tag, adopt it with the pin bump to the first tag that
    carries it; never mix a moving or newer ref into an otherwise exact-pin
    consumer. In particular, `0.1.0` carries `changelog-armed`,