Don't show Used n references when opening an old session

[daviddossett]

Fixes "Used n references" buttons appearing on restored agent-mode chats.

Problem

modeInfo was never serialized when saving chat sessions. When restoring old chats, modeInfo was always undefined, so the check modeInfo?.modeId === ChatModeKind.Agent in chatListRenderer.ts always evaluated to false, causing the "Used n references" button to show even for agent-mode sessions.

Fix

1. Persist modeInfo — Added modeInfo to ISerializableChatRequestData, toExport(), _deserializeRequest(), and the operation log schema so it survives across save/restore cycles.

2. Fallback for old sessions — For sessions saved before this change (no modeInfo on the request), fall back to the session-level delegate.currentChatMode() which reflects the persisted inputModel.mode.

[daviddossett]

@roblourens @justschen this went out of my comfort zone pretty quickly. Is this the right approach make sure Used n references doesn't show back up on reload/opening an existing session?

[Copilot]

Pull request overview

Persists per-request chat modeInfo into the chat session serialization/mutation-log format so restored sessions retain the correct mode context (notably to avoid showing “Used n references” for agent-mode history).

Changes:

• Add modeInfo to ISerializableChatRequestData and include it in request export/deserialize paths.
• Extend the chat session operation log schema to track modeInfo mutations.
• Adjust the references-part rendering logic to fall back to session mode when modeInfo is absent (backcompat for older sessions).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/vs/workbench/contrib/chat/common/model/chatSessionOperationLog.ts	Adds modeInfo to the request mutation-log schema so it is persisted in the incremental session log.
src/vs/workbench/contrib/chat/common/model/chatModel.ts	Extends serialized request shape and ensures modeInfo is exported and revived on restore.
src/vs/workbench/contrib/chat/browser/widget/chatListRenderer.ts	Uses modeInfo (or a fallback) to suppress references UI for agent-mode sessions on restore.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/common/model/chatModel.ts:2644

• modeInfo is now part of the persisted request data (toExport() + _deserializeRequest() + operation log). There doesn’t appear to be a unit test that covers a save/restore roundtrip with modeInfo present and missing (backcompat). Adding a test in the existing chat model serialization/normalization test suite would help prevent regressions like the one this PR fixes.

					agent: agentJson,
					timestamp: r.timestamp,
					confirmation: r.confirmation,
					editedFileEvents: r.editedFileEvents,
					modelId: r.modelId,
					modeInfo: r.modeInfo,
					...r.response?.toJSON(),

[roblourens]

This is not quite right because you can send a request to a participant while being "in agent mode". I'm going to do a slightly different fix, it's my fault this is messy

[daviddossett]

Thanks, knew this didn't feel good