fix: validate top_k in HuggingFaceTEIRanker

[Kunal-Somani]

Related Issues

• No related issue (discovered via code review and found a validation-parity gap across the rankers component family)

Proposed Changes:

HuggingFaceTEIRanker had no validation on its top_k parameter, unlike five of its six sibling ranker components (LLMRanker, LostInTheMiddleRanker, MetaFieldRanker, SentenceTransformersDiversityRanker, SentenceTransformersSimilarityRanker, TransformersSimilarityRanker), all of which raise ValueError(f"top_k must be > 0, but got {top_k}") for invalid values.

Confirmed via reproduction that HuggingFaceTEIRanker(url=..., top_k=0) and HuggingFaceTEIRanker(url=..., top_k=-5) both construct without error, and the invalid value silently flows into ranking logic via min(top_k or self.top_k, len(result)).

This PR adds the same validation pattern at:

• __init__ time (for the default top_k)
• run()'s optional top_k override
• run_async()'s optional top_k override

using the exact same validation logic and error message already used by the sibling components.

How did you test it?

• Reproduced the gap manually before writing the fix
• Ran the full test suite locally: PYTHONPATH="" hatch run test:unit test/components/rankers/test_hugging_face_tei.py — 16 passed
• Ran type checks: hatch run test:types — no issues in 365 source files
• Ran formatter: hatch run fmt — all checks passed
• Confirmed via git diff that the change is purely additive (+9 lines, 0 removed), with zero unrelated formatting changes to the existing file

Notes for the reviewer

Not a breaking change — no previously-valid top_k value is affected by this fix; only inputs that were already invalid (zero or negative) now fail clearly instead of silently producing broken behavior. Note that HuggingFaceTEIRanker is deprecated (moving to huggingface-api-haystack in 3.0), but its equally-deprecated siblings SentenceTransformersDiversityRanker and SentenceTransformersSimilarityRanker already maintain this same validation, so I kept it consistent here too.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/components/rankers
hugging_face_tei.py
Project Total

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[sjrl]

Hey @Kunal-Somani thanks for opening the PR! I do want to let you know that this component will be soon deprecated since we moved it to core integrations here https://github.com/deepset-ai/haystack-core-integrations/blob/a9aa83f1122a1e3ea3085b1d3c05090366ec700b/integrations/huggingface_api/src/haystack_integrations/components/rankers/huggingface_api/ranker.py#L31

So I'd recommend moving your PR to that repo with your fix.

[Kunal-Somani]

Hey @Kunal-Somani thanks for opening the PR! I do want to let you know that this component will be soon deprecated since we moved it to core integrations here https://github.com/deepset-ai/haystack-core-integrations/blob/a9aa83f1122a1e3ea3085b1d3c05090366ec700b/integrations/huggingface_api/src/haystack_integrations/components/rankers/huggingface_api/ranker.py#L31

So I'd recommend moving your PR to that repo with your fix.

Thanks for the advice, moving this to haystack-core-integrations with the same fix. Will close this PR.