Fix highlight priority handling and add consistency test

[nikhil2004-blip]

Fix highlight priority handling and add consistency test

Fixes: #6011

Overview

This PR fixes an issue where overlapping syntax highlight captures did not respect priority ordering, causing inconsistent styling for identical tokens depending on surrounding context.

A new deterministic priority system has been implemented so that when multiple highlight captures overlap on the same region, the correct one now consistently wins.

Additionally, a test has been added to ensure long-term correctness of this behavior.

Changes Included

1. Priority-based highlight conflict resolution

A new HIGHLIGHT_PRIORITY map defines stable ordering:

• Lower number = higher priority
• Specific captures (e.g., keyword.control) override generic ones (e.g., variable)

The new logic:

• Groups highlights by their (start, end) span
• Selects only the highest-priority highlight per span
• Applies highlight styles using the theme's syntax_styles
• This eliminates nondeterministic overwrites

2. New test: test_range_highlighting_priority_consistency

Added under:

tests/text_area/test_highlight_priority.py

This test verifies:

• The token range receives the same final highlight whether it appears alone or after another expression
• Conflicting captures produce identical resolved highlight output
• The priority rules work correctly and deterministically
• This protects against regressions

Checklist

• Docstrings on all new or modified functions / classes
• Updated documentation
• Updated CHANGELOG.md (where appropriate)

Note: Documentation and changelog can be updated after review.

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[TomJGooding]

It's been a while since I looked at the tree-sitter code, but I'm not convinced this is the correct fix.

Can I ask just for transparency: did you generate this PR with AI?

[nikhil2004-blip]

I used AI assistant to help me with wording and structuring the PR description, but the logic, debugging, and final code changes were done by me after understanding the issue.

I based the fix on reading through the text area, highlighting the area and verifying where priority resolution was happening
I also wrote a test for he issue

If something looks incorrect or could be better I
Am happy to work through it .

[TomJGooding]

From a quick test it doesn't look like this fixes anything:

I'm also pretty sure your test will pass even without your changes?

[nikhil2004-blip]

Can you guide me through it like what should I improve in it ..