Three fixes landing the PDF-slicing set coherently:
- bisect_slice read raw container bytes, so the adaptive-retry path (a lone oversized
slice that still overflows, #2880) searched for the newline cut in binary coordinates
and could cut mid-line for a compressed PDF. Index unit_source_text instead, matching
read_slice_text and expand_oversized_files; any converter failure falls back to None.
- #2900's test asserted a PDF is not splittable, which #2906 overturns; rewrite it to
guard the real invariant (an image has no addressable text and is never sliced). The
unreadable-PDF passthrough case is covered by test_pdf_slicing.
- add a bisect_slice-on-PDF regression test: the cut lands on an extracted-text line
boundary and the halves tile the slice exactly.
An oversized PDF was sliced as raw container bytes, so slice offsets indexed binary data
instead of the extracted text the prompt carries. Introduce unit_source_text so both the
oversized-file expansion and per-slice reads index the same extracted text, and make PDFs
splittable through the converter.
safishamsi