Fix truncation of degree-one vertex labels

[sjh9714]

Resolves #105.

Type of change

• Bug fix (non-breaking change which fixes an issue)

A degree-one vertex has identical start and end coordinates, but its rounded rectangle still has padding. The truncation check used the zero-width interval and replaced even a single digit with .... Measure the actual rectangle bounds, including padding, so labels that fit are retained. This leaves the vertex geometry and truncation algorithm unchanged.

Changes

Added

• tests/test_draw_labels.py: path and single-edge regressions through both draw entry points at the default and reported figure sizes, plus long-label truncation coverage.

Updated

• planarity/express/planarity.pyx: use the rounded rectangle's bounds for label width.

Testing

• .venv/bin/python -m pip install .
• .venv/bin/pytest -vv — 58 passed; the 10 new cases failed before the fix.
• .venv/bin/python -m build --outdir /tmp/creator-planarity-dist — sdist and wheel built.
• Inspected Agg-rendered PNGs for the path, single edge and long-label cases.

PATH="$PWD/.venv/bin:$PATH" .venv/bin/cython-lint planarity/express/planarity.pyx reports the same 10 pre-existing style violations before and after this change. Verified locally on macOS with Python 3.14.6; the other CI platforms/Python versions were not run locally.

[john-boyer-phd]

The difference between the right line of code and the almost right line of code can be like the difference between lightning and the lightning bug.
Good work, thank you!