copilotAgentSession: avoid leaking subscriptions when disposed during init

[roblourens]

Problem

Error: Trying to add a disposable to a DisposableStore that has already been disposed of. The added object will be leaked!
    at DisposableStore.add (lifecycle.js:327)
    at CopilotAgentSession._register (lifecycle.js:391)
    at CopilotAgentSession._subscribeForLogging (copilotAgentSession.js:1714)
    at CopilotAgentSession.initializeSession (copilotAgentSession.js:582)
    ...
    at async CopilotAgent._resumeSession
    at async CopilotAgent.getSessionMessages
    at async AgentService.restoreSession
    at async ChangesetSessionCoordinator.restoreSessionIfChangesetSubscription

CopilotAgentSession.initializeSession() is async. Between await this._wrapperFactory(...) resolving and the subsequent _subscribeToEvents() / _subscribeForLogging() calls, the session can be disposed (e.g. via _destroyAndDisposeSession). The subscribe methods then call _register on an already-disposed DisposableStore, producing the warning and leaking the freshly-created SDK session wrapper.

Fix

After the wrapper factory resolves, check this._store.isDisposed. If disposed:

• dispose the freshly-created wrapper (otherwise the disposed store warns and drops it on _register, leaking it), and
• throw CancellationError so callers (_materializeProvisional / _resumeSession) treat it as a cancellation rather than producing a half-initialized session.

(Written by Copilot)

[Copilot]

Pull request overview

This PR fixes a disposal race in CopilotAgentSession.initializeSession() where the session can be disposed while awaiting the SDK wrapper factory, causing _register() to be called on an already-disposed DisposableStore (warning + leaked wrapper/subscriptions). The change disposes the newly-created wrapper when this happens and throws CancellationError so callers treat the outcome as a cancellation rather than a partially-initialized session.

Changes:

• Create the SDK wrapper without immediately registering it, allowing a disposal check right after factory resolution.
• If the session was disposed during the await, dispose the wrapper and throw CancellationError.
• Otherwise register the wrapper and proceed to subscribe to events/logging as before.

Show a summary per file

File	Description
src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts	Adds a post-factory disposal check to prevent registering/subscribing on a disposed store; disposes wrapper and throws CancellationError on late disposal.

Copilot's findings

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

[DonJayamanne]

thanks was getting a model to look into this issue myself