DocLang output omits the namespace by default, so save_as_doclang_archive(validate=True) fails on any document

[DavidPivert]

DocLangParams.include_namespace defaults to False, so every DocLang produced by docling-core starts with <doclang version="0.7"> without xmlns="https://www.doclang.ai/ns/v0". The reference toolkit's XSD requires the namespace, which means docling-core's own validated archive export fails on a trivial document:

import tempfile
from docling_core.types.doc import DoclingDocument

d = DoclingDocument(name="t")
d.add_text(label="text", text="Hello")
d.save_as_doclang_archive(filename=tempfile.mkdtemp() + "/t.dclx", validate=True)

doclang.validation.ValidationError: XSD validation failed:
  Line 1: Element 'doclang': No matching global declaration available for the validation root.

Same with the CLI on export_to_doclang() output: doclang validate out.dclg fails (passes only with -n / --allow-empty-namespace), and doclang pack out.dclg --validate fails with no option to allow an empty namespace.

Suggestion: default include_namespace to True, or at least force it in save_as_doclang_archive() (the .dclx format requires a valid DocLang document.xml). Keeping it off for token-lean model input still makes sense, but as an opt-out.

Versions: docling-core 2.97.1 (also checked on main), doclang 0.7.3, Python 3.12, macOS.
Workaround we use: inject xmlns into the root before writing the file.