Enforcing Content-Type header on client requests

Typescript server I'm testing my Java SDK client with streamable HTTP against enforces client requests to server Content-Type header value of application/json, e.g.

      const ct = req.headers["content-type"];
      if (!ct || !ct.includes("application/json")) {
        res.writeHead(415).end(JSON.stringify({
          jsonrpc: "2.0",
          error: {
            code: -32000,
            message: "Unsupported Media Type: Content-Type must be application/json"
          },
          id: null
        }));
        return;
      }

I was fine with adding it, but the spec doesn't call out that requirement. It only dictates Content-Type header rules for the server's responses.

Is this something that should be added to the spec, or removed from the TS SDK server implementation?

Start by comparing the streamable HTTP Content-Type requirements in the protocol spec with the TypeScript SDK server implementation. Determine whether the client-request requirement belongs in the spec or should be removed from the SDK, and consider the issue complete when the decision and resulting behavior are documented consistently.