[SandObserver]

Summary

• Count every kept WebSocket fragment as at least 1 KiB toward the message limit in wrapSocket, so a server that streams empty or 1-byte continuation frames ends the session with Response too large instead of exhausting the API heap.
• Keep the byte count used to join the message separate from that budget.

Testing
All green. Added a test that 2,000 empty continuation frames end the session at a 1 MiB limit.

Changelog

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.