client-presence: Mark disconnected clientId to sessionId mappings

[WillieHabi]

Description

In this change we mark the disconnected clientId to sessionId in the system datastore once they are removed. This information will be useful to newly joined clients, as they can know which connectionIds are not in use anymore.

[Copilot]

Pull Request Overview

This PR adds a mechanism to mark disconnected client–session mappings in the system datastore so that newly joined clients can see which session IDs are no longer in use.

• Introduce an optional disconnected flag on ConnectionValueState
• Fetch and assert the existing session mapping for a client and set its disconnected flag when the client is removed

Comments suppressed due to low confidence (3)

packages/framework/presence/src/systemWorkspace.ts:222

• [nitpick] The variable name knownSessionID suggests it holds an ID string, yet it’s later treated as an object. Consider renaming it to sessionId and fetching the session state object into a separate variable for clarity.

		const knownSessionID = this.datastore.clientToSessionId[clientConnectionId];

packages/framework/presence/src/systemWorkspace.ts:225

• It would be good to add a unit test to verify that the disconnected flag is set correctly on the session state when a client is removed, ensuring this new flag behaves as expected.

		knownSessionID.disconnected = true;

packages/framework/presence/src/systemWorkspace.ts:225

• The value returned by clientToSessionId[clientConnectionId] is likely a primitive session ID (string), so assigning a disconnected property will fail at runtime. You should first retrieve the corresponding ConnectionValueState object from your datastore and then mark its disconnected flag.

		knownSessionID.disconnected = true;