feat: show total lines added/removed in task header

[roomote]

Related GitHub Issue

Closes: #11213

Description

This PR attempts to address Issue #11213 by adding aggregated line change stats (+added / -removed) to the TaskHeader component.

How it works:

• A new useDiffStats hook (webview-ui/src/components/chat/hooks/useDiffStats.ts) iterates through clineMessages, parses tool messages (ask="tool" and say="tool"), and extracts diffStats from file-editing tools (editedExistingFile, appliedDiff, newFileCreated). It also handles batchDiffs per-file stats. The result is memoized.

• Compact view (collapsed header): Shows +N / -N with green/red coloring next to the cost display, separated by a dot divider. Only shown when there are actual file changes.

• Expanded view (expanded header): Adds a "Lines Changed" row in the details table showing the same +N / -N stats, matching the existing visual pattern of the Tokens, Cache, and API Cost rows.

• Uses the existing text-vscode-charts-green and text-vscode-charts-red Tailwind classes, matching the CodeAccordian per-file diff display pattern already in use.

Test Procedure

• Unit tests for aggregateDiffStats (14 tests): Covers undefined/empty messages, ask/say tool messages, all file-edit tool types, batch diffs, malformed JSON, null text, and mixed message types.

  • Run: cd webview-ui && npx vitest run src/components/chat/hooks/__tests__/useDiffStats.spec.ts

• Integration tests for TaskHeader (6 new tests added to existing spec): Covers no diff stats shown when no edits, compact view display, expanded view display, aggregation across multiple messages, and zero-stat edge case.

  • Run: cd webview-ui && npx vitest run src/components/chat/__tests__/TaskHeader.spec.tsx

All 40 tests pass (14 hook + 26 TaskHeader including 6 new).

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue.
• Scope: Changes are focused on the linked issue.
• Self-Review: Self-reviewed.
• Testing: New tests added (14 unit + 6 integration).
• Documentation Impact: No documentation updates required.
• Contribution Guidelines: Read and agreed.

Documentation Updates

• No documentation updates are required.

Additional Notes

Feedback and guidance are welcome. This is an initial implementation covering the core feature. Future enhancements could include per-file breakdown in expanded view and an opt-out toggle setting.

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Important

Adds line change stats to TaskHeader with new useDiffStats hook and updates UI for compact and expanded views.

• Behavior:
  • Adds useDiffStats hook in useDiffStats.ts to calculate total lines added/removed from clineMessages.
  • Updates TaskHeader.tsx to display +N / -N in compact view and "Lines Changed" in expanded view.
  • Uses text-vscode-charts-green and text-vscode-charts-red for styling.
• Tests:
  • Adds 14 unit tests for aggregateDiffStats in useDiffStats.spec.ts.
  • Adds 6 integration tests for TaskHeader in TaskHeader.spec.tsx to cover various display scenarios.
• Localization:
  • Adds "Lines Changed" label to chat.json for i18n support.

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