fix: keep a CSV column named row_number in CSVToDocument row mode

[burakeyler]

Related Issues

Fixes #12787

Proposed Changes

_build_document_from_row merged the CSV columns into the metadata first and wrote the generated row_number afterwards, so a CSV column of that name was silently dropped:

ByteStream(data=b"text,row_number\nhello,record-42\n")
# meta before: {'row_number': 0}
# meta after:  {'row_number': 0, 'csv_row_number': 'record-42'}

The generated row number is now reserved before the merge, so the existing collision handling gives the CSV column the csv_ prefix like any other clashing column. Choosing row_number as the content column is unaffected, since the content column is skipped during the merge.

How did you test it?

Three tests added: the ordinary case, a case where csv_row_number and csv_row_number_1 are already taken (so the next suffix is used), and a control with content_column="row_number". The first two fail on main. pytest test/components/converters/test_csv_to_document.py → 20 passed.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title
• I documented my code
• I ran pre-commit hooks and fixed any issue

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[github-actions]

Hi @burakeyler, thanks for your interest in contributing to Haystack! 🙏

⛔ First-time contributors can have at most 1 open pull request in this repository until it has been approved, so this PR was closed automatically. Your open pull request #12879 is unaffected. Once it has been approved by a maintainer, you are welcome to open more PRs. Feel free to reopen this one at that point.

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[github-actions]

Hi @burakeyler, thanks for your interest in contributing to Haystack! 🙏

⚠️ Issue #12787 is already being addressed by open pull request(s) #12788. Before opening a PR for an issue, please check whether a PR is already linked to it, and consider contributing to the existing PR instead. We may close duplicate PRs to keep the review queue manageable.

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