Add local agent host test

[chrmarti]

#317981

[Copilot]

Pull request overview

Adds coverage for running the Agents Window against a local Agent Host (AHP) in smoke tests, and tightens several Agent Host/session-type synchronization behaviors to reduce UI/session churn during turns.

Changes:

• Add a new smoke test suite that launches the Agents Window and validates a “Local Agent Host” session end-to-end, including verifying AHP JSONL transcript output.
• Make the session-type picker automation resilient to late/async provider registration by polling for a specific label.
• Improve Agent Host session stability by (a) pinning in-flight subscriptions, (b) avoiding redundant “custom agents changed” events on non-agent root deltas, and (c) overlaying state-manager-announced sessions when providers transiently return empty listSessions() results.

Show a summary per file

File	Description
test/smoke/src/areas/agentsWindow/agentsWindow.test.ts	Adds a new smoke suite for local Agent Host sessions and validates AHP JSONL logging.
test/automation/src/agentsWindow.ts	Updates session-type picker automation to wait for a specific provider label to appear.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostSessionHandler.ts	Pins session subscriptions while awaiting first snapshot to avoid hangs if refcounts drop.
src/vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostChatContribution.ts	Adds a smoke-test-only auth token escape hatch gated by the smoke test driver flag.
src/vs/sessions/contrib/providers/agentHost/test/browser/localAgentHostSessionsProvider.test.ts	Extends tests to ensure “custom agents changed” only fires when the agents slice actually changes.
src/vs/sessions/contrib/providers/agentHost/browser/baseAgentHostSessionsProvider.ts	Suppresses custom-agent/customization change events unless the agents reference changes.
src/vs/platform/agentHost/node/agentService.ts	Overlays session summaries announced by the state manager when providers’ listSessions() snapshots transiently omit sessions.
src/vs/platform/agentHost/node/agentHostStateManager.ts	Exposes announced session summaries for AgentService fallback behavior.

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 1