chat: allow collapsing queued chat requests

[lakshaykhattar (LakshayKhattar)]

Long queued prompts take up chat space without a way to collapse them. Add a keyboard-accessible chevron that collapses each queued or steering message into a single-line preview. Each message keeps its own expansion state across rendering updates, queue reordering, and the transition into the transcript. Collapsed messages are excluded from sticky-scroll headers.

The local queue processor preserves request identity. When steering messages merge, the combined prompt inherits an explicit collapse choice from any source message; users can then expand or collapse the combined prompt normally. The collapsed hover exposes the full preview, and Chat Accessibility Help documents the keyboard controls.

Fixes #326123.

Validation:

• Browser renderer suite: 70 passing, 1 pre-existing skipped test, including 13 collapse regressions covering independent state, keyboard interaction, both chat layouts, merged steering, attachment visibility, and full-preview hover text.
• ChatService suite: 101 passing, covering real queue/dequeue paths, merged steering identities, slash-command retries, and blocked troubleshoot requests.
• Client transpilation, scoped ESLint, hygiene, and git diff --check passed.

To test:

1. Start a chat request that keeps streaming, then add two long follow-up messages using Add to Queue.
2. Collapse the first queued message with its Message chevron. It should become a single-line preview while the second stays expanded.
3. Use Enter and Space on the toggle, then leave the first message collapsed. Scroll and resize the chat while the response streams; its state should remain unchanged.
4. Let the first queued message begin processing. It should stay collapsed, and expanding it should restore the complete prompt.

Runtime evidence:

Watch the contributor's recording (MP4, 64 seconds). At approximately 0:48, one queued prompt is collapsed while the other remains expanded; at 0:55, both are collapsed independently while the current response continues streaming. The original recording is hosted as an evidence asset on the contributor's fork.

The recording shows the disclosure UI at commit 53e4074. The dequeue and merged-steering fixes in 49af945 are covered by the automated tests above.

[Copilot]

🟡 Changes recommended

The dequeue path loses collapsed state, with additional accessibility, URI comparison, hover, and CSS issues unresolved.

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

Pull request overview

Adds keyboard-accessible collapsing for queued and steering chat requests with per-message state preservation.

Changes:

• Adds collapse controls and single-line previews.
• Excludes collapsed messages from sticky-scroll headers.
• Adds renderer regression tests.

Review findings:

• Critical: The real dequeue path does not preserve request IDs, so collapsed state is lost when processing begins. Preserve/transfer state and test the actual path, including merged steering.
• Moderate: Compare session URIs using isEqual, not serialized strings.
• Moderate: Include the full truncated preview in the collapsed hover.
• Moderate: Remove the new prohibited !important styling.
• Nit: Document keyboard interaction in Chat Accessibility Help.

File summaries

File	Description
src/vs/workbench/contrib/chat/test/browser/widget/chatListRenderer.test.ts	Tests collapse state, layouts, keyboard use, and transitions.
src/vs/workbench/contrib/chat/browser/widget/media/chat.css	Styles collapsed request previews.
src/vs/workbench/contrib/chat/browser/widget/chatListRenderer.ts	Implements collapse state, controls, and sticky-scroll handling.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 5
• Review effort level: Balanced

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[lakshaykhattar (LakshayKhattar)]

Fixed in 49af945. The real dequeue path now preserves the pending request ID. Merged steering requests also carry their source IDs into the model/view model, so a collapse choice from any source transfers to the combined prompt; later expansion survives rerenders.

Added service regressions using the public queue/dequeue APIs, including automatic queued/steering dispatch, merged steering, slash commands and retries, and blocked troubleshoot requests. The renderer tests now complement those service tests instead of being the only evidence for the transition. All 101 ChatService tests and 70 renderer tests pass (one existing renderer test remains skipped).

[lakshaykhattar (LakshayKhattar)]

Fixed in 49af945: updateViewModel now uses the existing isEqual helper for session resources. The session-switch regression still passes as part of the renderer suite.

[lakshaykhattar (LakshayKhattar)]

Fixed in 49af945: the collapsed managed hover now includes the full normalized preview, using the localized "Expand Message: {0}" text. Added a regression that verifies the expanded hover and complete collapsed hover content.

[lakshaykhattar (LakshayKhattar)]

Fixed in 49af945. Removed the new !important rule and moved visibility handling into the renderer. It saves each request child's original display value, hides it on collapse, and restores that value on expansion.

The regression uses a real file attachment and verifies flex -> none -> flex, while the existing height and template-recycling tests continue to pass.

[lakshaykhattar (LakshayKhattar)]

Fixed in 49af945: added a localized paragraph to the existing Chat Accessibility Help explaining Tab/Shift+Tab navigation, Enter/Space activation, and independent queued-message collapse states. Scoped ESLint and hygiene checks pass.

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