fix(web): support multiline highlight ranges in LightweightCodeHighlighter

[riteshvish02]

Fixes #1698

Summary of Changes

Previously, LightweightCodeHighlighter filtered and mapped highlight ranges using a single-line check:

// @todo: we will need to handle the case where a range spans multiple lines.
const ranges = highlightRanges?.filter(range => {
    return range.start.lineNumber === lineNumber || range.end.lineNumber === lineNumber;
}).map(range => ({
    from: range.start.column - 1,
    to: range.end.column - 1,
}));

This caused issues when a highlight range spanned multiple lines:

• Intermediate lines between start.lineNumber and end.lineNumber were completely dropped, resulting in no highlighting.
• Start and end lines used column indices from different lines, which could produce inverted (from > to) or clipped ranges.

Solution

Introduced computeLineHighlightRanges(highlightRanges, lineNumber, lineLength) to correctly split multi-line 1-based SourceRanges into 0-based character slices for each line.

The new logic handles:

• Start line: Highlights from start.column - 1 to line.length.
• Intermediate lines: Highlights the entire line (0 to line.length).
• End line: Highlights from 0 to end.column - 1.
• Single-line range: Highlights from start.column - 1 to end.column - 1.
• Invalid/inverted ranges: Filters out ranges where to <= from.

Testing

Added comprehensive unit tests in:

packages/web/src/app/(app)/components/lightweightCodeHighlighter.test.ts

The tests cover:

• Single-line range highlighting on target lines.
• Multi-line range splitting across start, intermediate, and end lines.
• End-column clamping when the column exceeds the line length.
• Empty and invalid range filtering.
• Multiple highlight ranges on the same line.

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Note

Low Risk
Search-result UI highlighting only; behavior is covered by new unit tests with no auth or data-path changes.

Overview
Fixes multi-line search/match highlights in LightweightCodeHighlighter by replacing per-line logic that only considered start/end line numbers (and reused columns across lines) with exported computeLineHighlightRanges, which maps 1-based SourceRanges into per-line 0-based slices: partial highlight on the first and last lines, full-line highlight on lines in between, column clamping, and dropping empty ranges.

Adds Vitest coverage for single-line, multi-line, clamping, invalid ranges, and multiple ranges on one line. CHANGELOG notes the fix for highlights not covering every line in a multi-line range.

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Summary by CodeRabbit

• Bug Fixes
  • Code highlights now appear on every line covered by a multi-line range, rather than only on its first and last lines.
  • Highlight character positions stay within each line’s bounds, and empty or invalid ranges are omitted.
  • Multiple separate highlights on the same line remain distinct, while intermediate lines in a range are highlighted in full.

[coderabbitai]

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⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: f93b4ef4-c732-4e0c-a6ec-85dbb58d2f65

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Reviewing files that changed from the base of the PR and between 99962a4 and 61d2be1.

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📒 Files selected for processing (1)

• CHANGELOG.md

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 6042cea9-4056-4c65-995e-960acfdd19cc

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📥 Commits

Reviewing files that changed from the base of the PR and between 390e8b2 and 7fe000c.

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📒 Files selected for processing (2)

• packages/web/src/app/(app)/components/lightweightCodeHighlighter.test.ts
• packages/web/src/app/(app)/components/lightweightCodeHighlighter.tsx

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Walkthrough

LightweightCodeHighlighter now maps source ranges to bounded highlight offsets on each covered line. Intermediate lines are included. New tests cover empty, single-line, and multiline ranges, clamping, and multiple ranges.

Changes

Line highlight mapping

Layer / File(s)	Summary
Calculate and apply line highlight ranges packages/web/src/app/(app)/components/lightweightCodeHighlighter.tsx, packages/web/src/app/(app)/components/lightweightCodeHighlighter.test.ts	The new computeLineHighlightRanges helper converts source columns to bounded, zero-based offsets. The highlighter uses it for all lines covered by a range. Tests cover empty inputs, single-line and multiline ranges, clamping, empty ranges, and separate same-line ranges.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: brendan-kellam

Merge Risk: ⚪ Minimal · up to 7fe00

The change corrects multiline highlighting and adds focused range-mapping tests. No merge-blocking issue is established; merge after normal checks pass.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue [#1698] requires correct highlighting on start, intermediate, and end lines. computeLineHighlightRanges includes every covered line, maps the start line from start.column - 1 to lineLength…
Out of Scope Changes check	✅ Passed	The changes stay within issue [#1698]. The helper implements line-range mapping, and the added tests verify that behavior. No unrelated product behavior or unrelated files appear in the reviewed chang…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding multiline highlight support to LightweightCodeHighlighter.

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🧪 Generate unit tests (beta)

• Create a new PR

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