Claude Code closes ws MCP messages over 16 MiB: Sume sends URLs

Claude Code 2.1.295 (Oct 8) closes a websocket MCP connection when one message is over 16 MiB. Sume's hosted MCP is an HTTP endpoint at https://mcp.sume.com/mcp, and a finished job points to media on media.sume.com; the video bytes are not inside the tool result.

What is the rule?

The changelog entry is short: ws MCP messages over 16 MiB close the connection.

Where could a Sume result get big?

The result of jobs_result and the asset tools carries metadata and durable URLs on media.sume.com. A client downloads the file itself. Uploads work the other way: hosted MCP cannot read files from your laptop, so the flow is create an upload URL, PUT the bytes from the client, then complete the asset.

What to avoid in your own server

If you build a websocket MCP server alongside Sume:

• Return a URL, not a base64 body, for anything large.
• Use include_results: true on jobs_wait only for a handful of ids, since each completed id returns its result entry.

Does this affect HTTP servers?

The changelog line names websocket messages only. For a remote HTTP server such as Sume, the 16 MiB rule does not apply; the change in that release that does touch a remote HTTP connection is the backoff after drops in headless mode. Details on result shapes are in Jobs and results.