fix: count page breaks in overlapping regions once in RecursiveDocumentSplitter

[TimurRakhmatullin86]

Related Issues

No existing issue; found by code inspection.

Proposed Changes:

RecursiveDocumentSplitter counted every \f page-break in each emitted chunk when advancing its running page counter. With split_overlap > 0 the overlapping tail of a chunk is repeated verbatim at the start of the next chunk, so a page break inside that region was counted once per chunk containing it. Every chunk after such a break then carried a page_number shifted upward by one per repetition — sometimes exceeding the number of pages actually present in the document.

The fix advances the page counter only over the characters the next chunk does not repeat (chunk.count("\f", 0, len(chunk) - overlap_char_len)), mirroring how current_position is already advanced. Each chunk's own page_number still reflects the breaks within it, so the observable convention is unchanged. With split_overlap = 0, overlap_char_len is always 0 and behavior is bit-for-bit identical.

How did you test it?

Added test_run_count_page_breaks_once_with_overlap_split_unit_char: a two-page document ("This is page one.\fThis is page two, it is longer.") split with split_overlap=5, asserting the chunk contents and that the chunks following the overlapped break stay on page 2 instead of drifting to page 3+. The test fails without the fix (assert 3 == 2) and passes with it. ruff check and ruff format --check are clean on the changed files.

Notes for the reviewer

The change is orthogonal to the mid-chunk page-number convention discussion (e.g. the earlier #12590); it does not alter any existing test's expected page numbers, it only removes a double-count that could push page numbers past the real page count. This is the same bug class already fixed for MarkdownHeaderSplitter in #12619.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have added unit tests and updated the docstrings.
• I've used a conventional commit type for my PR title (fix:).
• I have added a release note file.

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Coverage report

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

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[bogdankostic]

Thanks for finding and reporting this, @TimurRakhmatullin86! The overlap drift is now fixed on main by #13006, which removed RecursiveDocumentSplitter's running page counter and calculates page_number from the chunk's offset instead, so a page break in an overlapping region can no longer be counted twice. Your reproduction is covered by test_run_page_number_does_not_drift_with_overlap. Closing as superseded.