Enhance agent merge widget for accessibility and interaction

[Lee Murray (mrleemurray)]

This refreshes the Agent Merge system-initiated chat turn so review feedback, failing checks, and merge status are easier to scan without exposing machine-facing content or persistent secondary chrome.

Changes

• Consolidate review comments, failing checks, conflicts, and branch status into a single severity-led summary.
• Left-align the widget, move the chevron to the trailing edge, use the standard pull request pill, and omit redundant section headings when only one issue type is present.
• Reveal the border, source metadata, and trailing controls together on header hover, keyboard focus, or expansion, without activating from the transparent outer stroke.
• Add a reduced-motion-aware source fade and preserve collapsed widget boundaries in high-contrast themes.
• Add an Agent Message toggle with a stable accessible name, pressed state, keyboard-only focus treatment, and non-sticky pointer focus.
• Attach the full summary hover to the interactive disclosure so truncated status text remains discoverable.
• Add an in-chat fixture using the production chat model, view model, and list widget path, alongside expanded, linked-comment, Markdown, and high-contrast scenarios.
• Update transcript labels, timeline expectations, and focused unit coverage.

Validation

• Focused Agent Merge unit tests passed.
• Targeted ESLint and Stylelint passed.
• VS Code editor diagnostics reported no errors.
• git diff --check passed.
• Component Explorer verified standalone, in-chat, hover, focus, expanded, conditional-section, Agent Message, and dark high-contrast states.

Known unrelated issue: Component Explorer can report duplicate registration of inlineChatWidget.statusPlaceholder during HMR reloads; the Agent Merge fixtures continue to render.

[Copilot]

🟡 Changes recommended

Multi-issue details omit the Review Feedback heading despite the described conditional-heading behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Refreshes the Agent Merge chat widget for clearer status scanning, interaction, and accessibility.

Changes:

• Consolidates merge status and adopts standard PR pills.
• Adds disclosure/toggle interactions, hover behavior, reduced-motion, and high-contrast styling.
• Expands fixtures and focused tests.

File summaries

File	Description
chatWidget.fixture.ts	Supports system-initiated fixture messages.
chatAgentMerge.fixture.ts	Adds interaction, theme, and in-chat scenarios.
chatAgentMergeContentPart.test.ts	Tests summaries, toggle state, and hover targeting.
promptTimelineModel.test.ts	Updates timeline expectations.
chatRequestText.test.ts	Updates transcript label expectations.
chatAgentMergeContent.css	Implements refreshed layout and interaction styling.
chatAgentMergeContentPart.ts	Reworks status, disclosure, message toggle, and PR rendering.

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Balanced

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[github-actions]

Screenshot Changes

Base: 3a01d742 Current: c3f71577

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1 insignificant change(s) omitted (≤20 px, Δ≤2). See CI logs for details.

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