Modal expands its Runtime with VM Sandboxes, Sidecars and generally available multi-node Clusters

What changed

Modal announced a set of Runtime updates on October 1. VM Sandboxes give agents a full Linux environment for Docker stacks, databases, dev servers and graphical tooling. Sandbox Sidecars place credentials, proxies and harness logic in same-host containers isolated from untrusted agent code. Modal Clusters are now generally available through `@modal.clustered` for coordinated multi-node jobs. The roundup also includes Sticky Sessions and Endpoint Candidates for stateful routing and inference-server comparisons.