[derek73]

Summary

python -m nameparser --locale ja took the pack but had no way to attach a segmenter, so it divided nothing and warned (rules/D1, the segmenterless-activation warning). It now attaches locales.ja_segmenter() when namedivider is installed:

$ python -m nameparser --locale ja --json "山田太郎"
{"title": "", "given": "太郎", "middle": "", "family": "山田", "suffix": "", "nickname": "", "maiden": ""}

• Only a missing package falls back. The CLI tests for namedivider with importlib.util.find_spec; any failure to load an installed one (numpy's ImportError, an OSError) propagates with its own message rather than being reported as "not installed".
• Without the extra the name reads as before, and the CLI prints nameparser: --locale ja divides unspaced names only with namedivider-python installed: pip install 'nameparser[ja]' in place of the parser's warning, which it filters by message: that warning's other remedies are code a command line cannot pass, and a print still shows under PYTHONWARNINGS=ignore.
• CLI only. parser_for(locales.JA) still needs segmenter=locales.ja_segmenter() and still warns without one. decisions/D1's new entry records the library-wide form as declined: the same code would parse 高橋一郎 differently with and without the extra, a Parser holding ja_segmenter() cannot be pickled (local closure), so parser_for(locales.JA) would stop pickling wherever the extra is installed, and the pack-and-segmenter pairing is explicit by design.
• Only the ja pack consults the factory.

Tests (tests/v2/test_cli.py)

In process, with the install stood in for so every branch runs in every environment: the segmenter attaches under ja and JA and survives each --order, with no warning; the missing extra prints the note once and warns nothing, with and without --order; a broken install fails with its own ImportError or OSError; zh never calls the factory. Plus one subprocess run per environment, each skipping where it cannot apply (the extra one runs only in the ja-extra job). Mutations checked against them: a broad except ImportError (3 fail), the segmenter dropped under --order (6), the warning not filtered (3), the factory called for every pack (1). #983's warns-once test is gone: the CLI no longer reaches that warning.

Docs: usage.rst's "has no way to attach one" paragraph rewritten, locales.rst's "equivalent to parser_for(locales.get(...))" qualified for ja, release-log bullet.

No parser behavior changes, so no rules or snapshot moves.

Test plan

• uv run pytest without the extra (34,158 passed)
• uv run --with 'namedivider-python>=0.4' pytest (34,181 passed)
• uv run mypy, uv run ruff check, sphinx-build -b html clean for the edited pages

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