* fix(xml): preserve DOCTYPE declaration when writing XML files
Pass `doctype=tree.docinfo.doctype` to all `ElementTree.write()` calls
so lxml does not silently drop the DOCTYPE on serialization. Also replace
`etree.tostring()` with BytesIO+write() in the diff and xmlstring paths
for consistency.
Fixes#2762
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
* test(xml): add integration test for DOCTYPE preservation
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
* feat(changelog): add fragment for xml DOCTYPE fix (#12148)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
