Enforcing Content-Type header on client requests

[ZachGerman]

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?