fix: raise ValueError for reversed page ranges in expand_page_range

[basilalshukaili]

Related Issues

No issue filed; found while reviewing the code.

Proposed Changes

expand_page_range silently drops pages when a reversed range (e.g. '7-5') appears alongside valid entries.

For example:

expand_page_range(["1-3", "7-5", "8"])
# Returns [1, 2, 3, 8]  — pages 5, 6, 7 silently lost, no error raised

When the reversed range is the only entry, the error message is misleading:

expand_page_range(["5-3"])
# Raises: ValueError: No valid page numbers or ranges found in the input list
# (says nothing about which range caused the problem or why)

The fix adds an explicit start <= end check immediately after parsing the two parts, raising a clear ValueError that identifies the offending range. All other code paths are unchanged.

How did you test it?

Added three new unit tests to TestExpandPageRange:

• test_reversed_range_alone_raises_value_error — single reversed range raises a clear, specific error
• test_reversed_range_mixed_raises_value_error — reversed range mixed with valid entries now raises instead of silently dropping pages
• test_equal_start_end_is_valid — confirms '3-3' (valid single-page range notation) still returns [3]

All existing tests continue to pass.

Notes for the reviewer

Change is limited to haystack/utils/misc.py (3 lines added, 2 refactored) and the corresponding test file. No behaviour change for valid inputs.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have added unit tests and updated the docstring is not needed (the docstring already says it raises ValueError for invalid ranges).
• I have added a release note.
• I used a conventional commit type (fix:) for the PR title.

AI-generated contribution: This PR was prepared with AI assistance. The bug was identified by code inspection and verified by running the function with the affected inputs.

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