Add more agenthost integration tests

[roblourens]

Co-authored-by: Copilot copilot@github.com

[Copilot]

Pull request overview

Adds additional end-to-end WebSocket integration tests for the Agent Host protocol to cover more session state behaviors (title changes, reasoning streams, and pending message handling), backed by new scripted behaviors in the mock agent.

Changes:

• Added integration tests for session title changes (client-dispatched and agent-generated) and persistence via listSessions.
• Added integration tests for reasoning events and for queued/steering pending-message flows.
• Extended the scripted mock agent to emit reasoning/title events and to simulate steering consumption.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/vs/platform/agentHost/test/node/protocolWebSocket.integrationTest.ts	Adds new E2E scenarios validating title updates, reasoning events, queued messages, and steering message consumption over the WebSocket protocol.
src/vs/platform/agentHost/test/node/mockAgent.ts	Extends the scripted mock agent to generate reasoning/title progress events and to consume steering messages for the new integration tests.