Fix off-by-one in decode_spans boundary check (#44584)
* Fix off-by-one in decode_spans boundary check
When `len(scores_flat) == topk`, `np.argpartition` is called with
`kth=topk` which is out of bounds (0-indexed). Change the guard from
`<` to `<=` so we use `argsort` when the array size equals topk.
Fixes #44327
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
* Revert test addition per reviewer request
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Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
