fix: close SSE stream immediately

[paoloricciuti]

Right now, the SSE stream sits basically unused (since it's really only used for list changed notification and logging, both of which we don't even have in the capabilities). But since we are hosting on Vercel, it times out after 300 seconds, leaving a nasty log in the observability panel.

Doing this will immediately close the stream and return an empty string (or the MCP inspector will yell at us) so that we don't waste Vercel resources and we don't have nasty logs.

The downside is obviously that if, in the future, we want to send notifications or logs, we have to remember to re-enable it.

Btw, testing this I:

1. Found a bug in the session manager implementation that I fixed (hence the upgrade dependency)
2. Realised that, given we only support HTTP streaming, we can actually use Elicitation and Sampling since those are sent back on the same stream of the POST request. We might not even need the Redis instance since with Fluid Compute, it should go to the same lambda, but we'll see if we ever go that route.

I would say this is good for the moment, but I want to hear if anybody is against it.

[vercel]

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Project	Deployment	Preview	Comments	Updated (UTC)
mcp	Ready	Preview	Comment	Sep 20, 2025 10:01pm