Fix agent host worktree metadata timing

[roblourens]

Fix #322529

Summary

• update cached Agent Host session adapters when materialization publishes the final worktree
• defer Git-state refreshes until a session leaves the creating lifecycle
• overlay live workspace metadata on session-list snapshots and persist remote adapter updates
• notify session-list consumers when Git metadata changes

Validation

• npm run typecheck-client
• focused and complete AgentService/Git-state/local-provider/remote-provider unit suites (303 passing, 28 pending)
• npm run valid-layers-check
• hygiene checks
• isolated Agents window validation: final worktree path in SessionAdded, corrected branch metadata 185ms later and before turn completion

(Written by Copilot)

[Copilot]

Pull request overview

This PR fixes a timing problem where Agent Host sessions surfaced stale worktree/branch metadata during session creation and materialization. When a session is created, its provisional working directory is the selected checkout, not the final isolated worktree; the metadata (project, working directory, Git branch) only becomes authoritative once materialization completes. The changes ensure the cached session adapters and the session-list snapshot reflect the final materialized state, and that Git-state refreshes don't run against the transient checkout.

Changes:

• Treat notify/sessionAdded as an authoritative upsert: update an already-cached adapter in place (via a new updateAdapter hook) and report it as changed, instead of ignoring duplicates.
• Defer refreshSessionGitState while a session's lifecycle is Creating, and overlay live workspace metadata (modifiedTime, project, workingDirectory) onto listSessions snapshots.
• Persist remote adapter updates and fire onDidChangeSessions when session _meta (Git state) changes.

Show a summary per file

File	Description
src/vs/platform/agentHost/node/agentHostGitStateService.ts	Skips Git-state refresh while the session is in the Creating lifecycle.
src/vs/platform/agentHost/node/agentService.ts	Overlays live modifiedTime/project/workingDirectory from the state manager summary onto list snapshots.
src/vs/sessions/contrib/providers/agentHost/browser/baseAgentHostSessionsProvider.ts	Makes sessionAdded an upsert, adds the updateAdapter hook, and fires change events on meta changes.
src/vs/sessions/contrib/providers/remoteAgentHost/browser/remoteAgentHostSessionsProvider.ts	Overrides updateAdapter to refresh the persisted metadata cache and mark it dirty.
src/vs/platform/agentHost/test/node/agentHostGitStateService.test.ts	Adds coverage for deferring Git state while creating.
src/vs/platform/agentHost/test/node/agentService.test.ts	Adds coverage for overlaying live metadata over a stale snapshot.
src/vs/sessions/contrib/providers/agentHost/test/browser/localAgentHostSessionsProvider.test.ts	Adds in-place upsert and Git-meta notification tests; renames the dedup test.
src/vs/sessions/contrib/providers/remoteAgentHost/test/browser/remoteAgentHostSessionsProvider.test.ts	Adds a persistence test for materialized workspace metadata.
src/vs/sessions/SESSIONS.md / AGENT_HOST_SESSIONS_PROVIDER.md	Document the authoritative-upsert and deferred Git-state behavior.

Review details

• Files reviewed: 10/10 changed files
• Comments generated: 0
• Review effort level: Medium