The commit page built its "co-authored by" list from
`AllParticipantIdentities()[1:]`, which only drops the author and leaves
the committer in the list even though the committer is already shown
separately as "committed by". This caused the committer to be wrongly
rendered as a co-author (issue #38384): a commit authored by
`silverwind`, committed by `bircni`, with a `Co-authored-by: silverwind`
trailer displayed "co-authored by bircni" instead of the actual trailer
identity. This adds a `Commit.CoAuthorIdentities()` method that excludes
both the author and the committer, uses it on the commit page, and
covers the fix with a regression test.
Closes#38384
Parse `Co-authored-by:` trailers from commit messages and surface
contributors as an avatar stack across the commit page, commits list, PR
commits tab, latest-commit row, blame, graph, and dashboard feed.
- Up to 10 visible 20px avatars, GitHub-style overlap (6px first stride,
4px between subsequent), `+N` chip for the rest.
- Label: 1 → name; 2 → `<a> and <b>`; 3+ → `<N> people` opens a Tippy
popup with all participants.
- Names and avatars link to the repo's commits-by-author search; fall
back to profile or `mailto:`.
- Trailer parsing uses `net/mail.ParseAddress`, scans only the trailing
paragraph, filters out the commit's own author/committer.
- Drops the non-standard `Co-committed-by:` emission on squash merge and
web edits.
Devtest: `/devtest/coauthor-avatars`.
Fixes#25521
----
<img width="353" height="277" alt="image"
src="https://github.com/user-attachments/assets/72092ceb-97ca-4b09-9557-0b72d3c5458e"
/>
<img width="533" height="328"
src="https://github.com/user-attachments/assets/11d0c8f8-8b3f-4f2e-9993-879f1c06bcc5"
/>
---------
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>
