fix(overlay): correct padding, ANSI clipping, and Unicode rendering

[frittlechasm]

Pull Request

Description

Fixes overlay rendering issues found while adding test coverage in #71. The fixes address ignored bottom padding, incorrect character alignment, duplicated ANSI escape bytes, and custom whitespace rendering.

Changes Made

• Honor vertical padding for bottom-right overlays.
• Preserve alignment when clipping through double-width characters.
• Prevent duplicate ANSI escape bytes while preserving styles and resets.
• Render custom whitespace without exceeding the available width and handle patterns containing only zero-width characters.
• Add regression tests with exact output assertions.

Testing

• Tests from #71 also pass when combined with these fixes.
• ran locally on macOS
• Tested locally with example workflows
• Added new tests (if applicable)
• Tested with different filters, output, etc...

Checklist

• I have starred the repository
• My code follows the project's code style
• I have updated the documentation (README, cli-flags, etc...)
• My changes generate no new warnings
• I have tested my changes in a real workflow
• All tests pass locally

Greptile Summary

This PR corrects bottom-right overlay placement and strengthens ANSI-aware clipping, Unicode cell-width handling, and custom whitespace rendering. Focused rendering checks confirmed the updated behavior across styled wide glyphs, combining characters, and zero-width whitespace patterns.

Confidence Score: 5/5

Safe to merge: no blocking issues were identified in the changed overlay behavior.

The completed focused rendering checks passed on the PR revision, and no actionable issues remain.

Files Needing Attention: None.

T-Rex Logs

What T-Rex did

• Ran the edge-case validation test for PR72 overlay and captured the before-state results showing two edge-case checks not met.
• Compared the after-state results with the PR head and confirmed all edge-case checks pass.
• Reviewed the authored and executed test source that drives this validation to confirm its scope and intent.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "fix(overlay): preserve padding and unico..." | Re-trigger Greptile}