find_tables() default (use_layout=True) misses ruled tables that use_layout=False finds #5225

Description of the bug

With pymupdf-layout installed, Page.find_tables() in PyMuPDF 2.0 defaults to the layout-based finder (use_layout=True). On a set of born-digital service manuals with fully ruled tables (vector cell borders), that finder returns no table, while the line-based finder (use_layout=False, the 1.28.x behaviour) finds the full grid.

Across 36 affected pages from 8 PDFs:

Example page: a 14×4 ruled table at bbox (89, 57, 561, 699). 1.28.2 → 14×4; 2.0 default → none; 2.0 use_layout=False → 14×4. pymupdf4llm.to_markdown(..., table_output="html") still emits the table on all 36 pages, so the layout model does recognise it there.

Bisect on that page under 2.0 default: removing any one of 7 text blocks restores detection (two large rotated watermark blocks in a condensed font, three cell texts that run past a column rule, two multi-line blocks in one column). Replacing all text with same-size x placeholders also restores it. So it looks like a combined or threshold condition, not one bad object.

Not reproduced synthetically: the following all detect correctly in both versions — filled-rect rules (black, grey, even-odd), stroked grid plus one rotated watermark, and a sweep of 0–2 watermarks × 0–10 overflowing cells. The source PDFs are confidential, so I cannot attach them; happy to run diagnostics locally.

How to reproduce the bug

import pymupdf
page = pymupdf.open("affected.pdf")[506]
print(len(page.find_tables().tables))                  # 2.0: 0
print(len(page.find_tables(use_layout=False).tables))  # 2.0: 1 (14x4)

PyMuPDF version

2.0 (pymupdf-layout 2.0, pymupdf4llm 2.0); compared against 1.28.2

Operating system

macOS

Python version

3.13