[FanWu-ai]

Problem

HighlightMatchingBracketProcessor compares a transformed display column with the original cursor column, without checking the source row. For (\n), both brackets receive the cursor style when the cursor is on either bracket. When a previous processor inserts a prefix, the bracket under the cursor instead receives the other-bracket style.

Change

Determine whether a bracket is under the cursor using its source row and column, before mapping its column into display coordinates.

Regression coverage

Test the cursor on either bracket of a multiline pair, both without a prefix and with a source-to-display offset. Also preserve the existing other-bracket style when the cursor is immediately after the closing bracket, for single-line and multiline pairs.

AI-assisted implementation; the patch and test results were reviewed.

Validation

• Unmodified base: 156 tests passed; project lint, formatting, spelling, all three strict mypy platform checks and all pre-commit hooks passed.
• Regression against unmodified HighlightMatchingBracketProcessor: 4 failed, 4 passed.
• Fixed tree: 164 tests passed; ruff check, ruff format --check, typos, mypy --strict for win32/linux/darwin, all 12 prek hooks, and git diff --check passed.
• Independently reviewed with additional focused checks.
• Local runtime: Python 3.12.14 on Linux. Hosted CI has not yet run for this PR.

Commands run successfully against the final tree:

.venv/bin/coverage run -m pytest tests/
.venv/bin/ruff check .
.venv/bin/ruff format --check .
.venv/bin/typos .
.venv/bin/mypy --strict src/ --platform win32
.venv/bin/mypy --strict src/ --platform linux
.venv/bin/mypy --strict src/ --platform darwin
PREK_HOME=/tmp/prek-c .venv/bin/prek run --all-files
git diff --check

Packaging validation: .venv/bin/python -m build passed in an isolated build environment and produced both the sdist and wheel. Setuptools emitted deprecation warnings concerning upstream license classifiers; the build completed successfully.