Support multi-root Agent Host session metadata

[DonJayamanne]

Summary

• send and persist the originating multi-root workspace URI and name in Agent Host session metadata
• use workspace-file identity for Editor-window multi-root session filtering
• cover direct, provisional, rebound, fork, restore, and startup-cache paths
• remove the temporary workspace-scoped membership memento

The corresponding Agent Host Protocol request metadata change was merged in microsoft/agent-host-protocol#379. This PR intentionally does not update .ahp-version: a full sync from current AHP main also includes unrelated protocol 0.8 changes that require a separate referenced ToolInput adoption.

Out of scope

Agents Window workspace grouping and disabling the workspace-section + action will be handled in a separate PR.

Validation

• npm run typecheck-client
• npm run valid-layers-check
• npm run precommit
• focused Agent Host transport, lifecycle, persistence, filtering, and cache unit tests
• AHP npm test, Rust clippy, and cargo test --workspace

[Copilot]

Pull request overview

Replaces the temporary workspace membership memento with durable Agent Host multi-root workspace metadata.

Changes:

• Forwards and validates _meta.multiRoot during session creation.
• Persists metadata across forks, restoration, and startup caching.
• Filters Editor sessions by workspace-file identity.

Show a summary per file

File	Description
.github/skills/sessions/SKILL.md	Documents metadata-based filtering.
src/vs/platform/agentHost/browser/remoteAgentHostProtocolClient.ts	Sends creation metadata.
src/vs/platform/agentHost/common/agentService.ts	Adds creation metadata API.
src/vs/platform/agentHost/common/state/protocol/common/commands.ts	Adds protocol request metadata.
src/vs/platform/agentHost/common/state/sessionState.ts	Defines validated multi-root metadata helpers.
src/vs/platform/agentHost/node/agentService.ts	Persists, restores, and inherits metadata.
src/vs/platform/agentHost/node/protocolServerHandler.ts	Forwards protocol metadata.
src/vs/platform/agentHost/test/common/sessionWorkspacelessMeta.test.ts	Tests metadata validation.
src/vs/platform/agentHost/test/electron-browser/remoteAgentHostProtocolClient.test.ts	Tests client forwarding.
src/vs/platform/agentHost/test/node/agentService.test.ts	Tests persistence and restoration.
src/vs/platform/agentHost/test/node/protocolServerHandler.test.ts	Tests server forwarding.
src/vs/sessions/contrib/providers/agentHost/AGENT_HOST_SESSIONS_PROVIDER.md	Documents persistence behavior.
src/vs/sessions/contrib/providers/agentHost/browser/baseAgentHostSessionsProvider.ts	Preserves metadata in startup cache.
src/vs/sessions/contrib/providers/agentHost/test/browser/localAgentHostSessionsProvider.test.ts	Adds cache coverage.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionHandler.ts	Adds metadata to direct creation.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionListStore.ts	Uses workspace-file filtering.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostUntitledProvisionalSessionService.ts	Creates Editor workspace metadata.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostWorkspaceSessionMembershipStore.ts	Removes the membership memento.
src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostChatContribution.test.ts	Updates filtering and creation tests.
src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostUntitledProvisionalSessionService.test.ts	Tests provisional metadata paths.
src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostWorkspaceSessionMembershipStore.test.ts	Removes obsolete memento tests.

Review details

• Files reviewed: 21/21 changed files
• Comments generated: 3
• Review effort level: Balanced

[Copilot]

Review details

Suppressed comments (2)

src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostUntitledProvisionalSessionService.ts:306

• This folder-count gate drops provenance for sessions created after a .code-workspace is reduced to one (or zero) folders. WorkbenchState.WORKSPACE is determined by the presence of workspace.configuration, not by folder count (configurationService.ts:184-192), so those are still workspace-file sessions; unlike sessions created before the folder change, they fall back to path filtering and can disappear when folders change again. Remove the folder-count condition and key this metadata solely on the workspace-file identity.

			|| workspace.folders.length < 2

src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionListStore.ts:377

• extUriBiasedIgnorePathCase treats every non-file scheme as case-insensitive (resources.ts:340-343). For the remote workspace URIs this feature explicitly supports, two distinct case-sensitive paths such as /work/Demo.code-workspace and /work/demo.code-workspace therefore compare equal and expose the wrong workspace's sessions. Inject IUriIdentityService and compare with its provider-aware extUri.isEqual instead.

				&& extUriBiasedIgnorePathCase.isEqual(URI.parse(multiRoot.workspaceFile), workspace.configuration);

• Files reviewed: 21/21 changed files
• Comments generated: 0 new
• Review effort level: Balanced