agentHost: Restore selected model across sessions

[roblourens]

Restores the selected model across agent-host session surfaces by carrying model metadata through backend session summaries, websocket list responses, local/remote session providers, and restored chat history.

Summary:

• Add model metadata to agent-host session list/create/fork/restore paths.
• Remove picker-owned model storage so model state is owned by sessions/providers.
• Propagate restored model ids into chat history so the chat widget model picker restores through existing chat input state.
• Add provider unit coverage and a websocket protocol integration test for model summary propagation.

Validation:

• Focused unit tests: 154 passed.
• Targeted websocket integration: session model flows through create, subscribe, listSessions, and modelChanged passed.
• Core Typecheck latest: 0 errors.
• Direct hygiene on touched files passed.
• npm run valid-layers-check passed.

(Written by Copilot)

[Copilot]

Pull request overview

This PR restores the selected language model across agent-host-backed session surfaces by propagating model metadata end-to-end (agent host session summaries → protocol list responses → sessions providers → restored chat history), and by shifting model selection ownership from the picker to the sessions/providers.

Changes:

• Add model metadata to agent-host session metadata, protocol listSessions output, and session create/fork/restore flows.
• Plumb restored model ids into chat session request history so the chat widget’s model picker can restore selection via existing chat input state mechanisms.
• Add/extend unit and integration tests covering model propagation (local/remote providers + WebSocket protocol integration).

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/test/browser/agentSessions/stateToProgressAdapter.test.ts	Adds coverage ensuring restored request history includes modelId.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/stateToProgressAdapter.ts	Extends history restoration to attach modelId to request items.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionHandler.ts	Threads model id into restored history and into fork creation path; adds helper to normalize model ids.
src/vs/sessions/contrib/remoteAgentHost/test/browser/remoteAgentHostSessionsProvider.test.ts	Adds tests for model metadata on list/notifications and model-change action handling.
src/vs/sessions/contrib/remoteAgentHost/browser/remoteAgentHostSessionsProvider.ts	Surfaces session model as observable state; adds setModel and handles SessionModelChanged.
src/vs/sessions/contrib/localAgentHost/test/browser/localAgentHostSessionsProvider.test.ts	Adds tests for local provider model propagation and SessionModelChanged handling.
src/vs/sessions/contrib/localAgentHost/browser/localAgentHostSessionsProvider.ts	Surfaces session model as observable state; adds setModel and handles SessionModelChanged.
src/vs/sessions/contrib/copilotChatSessions/browser/copilotChatSessionsActions.ts	Removes picker-owned storage and drives picker selection from active session’s modelId.
src/vs/platform/agentHost/test/node/protocol/sessionFeatures.integrationTest.ts	Adds WebSocket integration test asserting model flows through create/subscribe/list/modelChanged.
src/vs/platform/agentHost/node/protocolServerHandler.ts	Includes model in protocol listSessions responses.
src/vs/platform/agentHost/node/copilot/copilotAgent.ts	Adds model persistence/restore into session listing and resume/recreate flows.
src/vs/platform/agentHost/node/agentService.ts	Ensures live session state model is reflected in metadata and session summaries.
src/vs/platform/agentHost/common/agentService.ts	Extends IAgentSessionMetadata to include optional model.

Copilot's findings

• Files reviewed: 13/13 changed files
• Comments generated: 3

[github-actions]

Screenshot Changes

Base: 689454c4 Current: 6eb8fde2

Changed (2)

editor/inlineCompletions/other/JumpToHint/Dark

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agentSessionsViewer/ApprovalRowLongLabel/Dark

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