Aegra: Cross-user run injection in /threads/{thread_id}/runs (IDOR)

Aegra is a drop-in replacement for LangSmith Deployments. Prior to 0.9.7, with multiple authenticated users on a shared instance are vulnerable to a cross-tenant IDOR. Any authenticated attacker, given another user's thread_id, can execute graph runs against the user's thread, read the user's full checkpoint state, and inject arbitrary messages into the user's conversation history. This vulnerability is fixed in 0.9.7.