fix: keep EmbeddingBasedDocumentSplitter.run_async on the async path

[pcbeingused333]

Related Issues

• No issue; found while reading the component.

Proposed Changes:

EmbeddingBasedDocumentSplitter._split_document_async is only async for the first pass:

splits = await self._split_text_async(text=doc.content)
merged_splits = self._merge_small_splits(splits=splits)
final_splits = self._split_large_splits(splits=merged_splits)   # synchronous

_split_large_splits re-splits every chunk that came out longer than max_length by calling _split_text, which calls _calculate_embeddings, which calls self.document_embedder.run(...). So in run_async the recursion embeds through the blocking path, on the event loop, once per over-long chunk and again at every level of the recursion.

This is not an edge case — max_length is the setting whose whole purpose is to trigger that recursion, and the sync path is identical up to that point, so the async version silently behaves like the sync one for the most expensive part of the work.

Added _split_large_splits_async, mirroring the sync version but awaiting _split_text_async, and called it from _split_document_async. The sync path is untouched.

How did you test it?

• New unit test test_recursive_split_of_large_chunks_stays_async: a recording embedder that implements both run and run_async, and a document long enough that the first pass produces a chunk over max_length. The test asserts the async path is used more than once (so the recursion did happen) and that run is never called. On main it fails with sync == 1.
• hatch run test:unit — 6116 passed, 10 skipped.
• hatch run test:types and hatch run fmt clean.

Notes for the reviewer

The two _split_large_splits methods are near-duplicates, which I kept deliberately: the alternative is to thread an "am I async" flag through the recursion, and the sync/async pairs elsewhere in this file (_split_document, _split_text, _calculate_embeddings) are written the same way.

I used an AI assistant while writing this change. I have reviewed it, reproduced the behaviour, and run the tests.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title.
• I have documented my code.
• I have added a release note file.
• I have run pre-commit hooks and fixed any issue.

[vercel]

Someone is attempting to deploy a commit to the deepset Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

All committers have signed the CLA.

[HaystackBot]

Hi @pcbeingused333, thanks a lot for your contribution! 🙏

We noticed that the Contributor License Agreement (CLA) check (license/cla) hasn't passed yet, so we've temporarily moved this PR to draft and paused the review assignment.

To get your PR reviewed, please sign the CLA via the link in the license/cla check below (or in the CLA bot comment). As soon as the check turns green, this PR will automatically be marked ready for review again and a reviewer will be re-assigned.

[pcbeingused333]

recheck

[HaystackBot]

Thanks for signing the CLA, @pcbeingused333! 🎉 This PR is now ready for review again and the reviewer has been re-assigned.