Remove deprecated empty-session-on-missing behavior from GET working-memory

[abrookins]

Summary

The deprecated behavior in GET /v1/working-memory/{session_id} that returns an empty working memory instead of 404 for missing sessions should be removed.

Current Behavior

When a session doesn't exist, the API returns a new empty WorkingMemory object with new_session: true instead of returning 404. This was kept for backward compatibility with older clients.

Problem

This behavior masks bugs where clients use mismatched parameters between PUT and GET:

1. Client PUTs working memory with namespace=default, user_id=default
2. Client GETs with namespace=default but no user_id
3. Server looks for different key, doesn't find it
4. Instead of 404, returns empty session - client thinks data was lost

The warning log shows:

Client version X using deprecated behavior. GET /v1/working-memory/{session_id} will return 404 for missing sessions in version 1.0.

Proposed Change

Remove the deprecated behavior and return 404 for missing sessions. Clients should use getOrCreateWorkingMemory if they want create-on-read semantics.

Related

This was discovered while investigating a bug where the JS client's getWorkingMemory didn't pass user_id as a query parameter, causing key mismatches.