chore: release main - #135

* ci(release): accept only merge commits on main

A squashed promote collapses the week's commits into one hidden `ci:`
subject, so release-please reports no user-facing commits and the
entries vanish from the notes; it also collapses authorship onto whoever
merged. A rebase breaks the merge base the back-merge relies on.

The ruleset file now allows only merge commits on main. A bypass in
pull_request mode does not lift that restriction (proven in a sandbox),
so the Release PR moves from --squash --admin to --merge --admin, which
this repository already released from once (#135). The live ruleset is
left unchanged: it must be applied only after one release has merged
with --merge.

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

* feat(release): credit each release line's commit author

Generated GitHub releases never named the people behind a change.
release-please's own include-commit-authors option is a no-op in every
17.x release so far: parseConventionalCommits drops the author before
the changelog notes see it (googleapis/release-please#2761, fix pending
in #2892).

After release-please creates the cycle's releases, a CI step appends
each line's commit author as (@login), or the name when no account
resolves, resolved from the line's commit SHA. Lines already credited
are left alone, so a re-run changes nothing, and a crediting failure
never blocks the build and publish jobs. Delete the step once a fixed
release-please is pinned.

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

* docs(release): state the merge-only rule as declared, not live

The live main ruleset still allows squash and rebase until a maintainer
applies .github/rulesets/main.json, which must wait for one release to
merge with --merge. The docs now describe the rule the file declares
instead of claiming it is enforced today.

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

* fix(release): make release crediting fail loudly and never block publishing

A missing RELEASE_OUTPUTS made the script credit nothing and exit 0, and
a failing checkout before the credit step would fail the release-please
job and skip every build and publish job. The script now exits non-zero
on missing outputs, both crediting steps carry continue-on-error, and
tests pin the wiring. A second pass no longer re-appends an author name
containing parentheses, and a release is written back only when its
body changed.

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

* fix(release): merge into main with an empty commit body

The repository fills a merge commit's body with the PR title, and
release-please splits a message on each conventional line, so a PR
merged into main as a merge commit is parsed twice: the change appears
twice in the notes, the copy credited to whoever merged. No repository
setting yields an empty body with the "Merge pull request" subject.

The Release PR and promote merges now pass --body "", and hotfixes are
documented to merge with an empty description. Proven in a sandbox: a
default-body merge duplicated the line, an empty-body merge did not.

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

* fix(release): drop merge-commit duplicates when crediting releases

A hotfix merged with the default body still reaches release-please
twice. When crediting, a line whose commit is a merge commit is removed
if a non-merge line in the same release carries the same text; a lone
merge-commit line is credited to its pull request's author instead of
whoever merged it. CHANGELOG.md keeps the duplicate.

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

* refactor(release): shorten the release crediting comments

Refs #911

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
AIDD-Session-Id: 3adb1fb2-3894-4e52-afab-424803c7fcad

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Co-authored-by: Claude Opus 5.5 (1M context) <[email protected]>