`gitea dump -f backup.tar.gz` without `--type` wrote a zip archive under
that name. Detecting the type from the file name was requested in
https://github.com/go-gitea/gitea/issues/24622 and intended in
https://github.com/go-gitea/gitea/pull/30240, but the check read the
still-empty result instead of `--file`, so every name fell back to zip.
A supported extension now selects the type, other names like `backup` or
`gitea.bak` still default to zip. An explicit `--type` still wins, and
its help text now mentions the detection.
AI disclosure: written with Claude Code (claude-opus-5-5).
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Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: silverwind <me@silverwind.io>