Polish multi-file diffs in Agents window

[romalpani]

Summary

• Present each changed file as an inset, rounded card in the Agents Changes view.
• Show secondary file actions on hover or focus and align the collapse control with toolbar actions.
• Highlight only the focused card with subtle, theme-aware active and keyboard-focus states.
• Expand collapsed cards before running full-file expand or collapse actions.
• Add bottom scroll clearance so the final card is not obscured by the horizontal scrollbar.

Before:

After:

CleanShot.2026-07-24.at.20.50.20.mp4

Validation

• Core transpilation and extension build pass.
• Changes action tests pass (7 tests).
• Precommit hygiene and diff checks pass.
• Full typecheck remains blocked by unrelated existing Copilot SDK and Agent Host errors.

[Copilot]

Pull request overview

Polishes multi-file diff cards in the Agents Changes view and improves collapsed-file actions and scrolling.

Changes:

• Adds inset card styling, contextual actions, and focus states.
• Expands collapsed cards before full-file actions.
• Adds configurable bottom scroll clearance.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
sessionChangesEditor.ts	Configures bottom clearance.
multiFileDiffEditor.css	Styles cards, actions, and focus states.
changesActions.ts	Expands cards before file-wide actions.
multiDiffEditorWidgetImpl.ts	Includes bottom padding in scroll height.
multiDiffEditorWidget.ts	Exposes bottom-padding configuration.