Provide notification of server connection loss

[AArnott]

Is your feature request related to a problem? Please describe.

A client should be notified when a STDIO server unexpectedly terminates (e.g. a crash) so that tool lists can be updated and optionally restart the server.

Describe the solution you'd like

Add an Exited event to StdioClientTransport. It should provide the exit code and at least the tail of the STDERR from the process as well, similar to what you did for #362. The idea being we can include any crash data in the logs for user inspection to resolve whatever issue led to the crash.

[prasethu]

@stephentoub can this be scheduled sometime soon?

[stephentoub]

I will try to get to it soon.

[AArnott]

We now have a customer report that leads us to need notification when SSE transports terminate as well.

Can you design a notification within the transport abstraction so that it works regardless of individual transport? And the transport implementation can decide what details to report on.

[stephentoub]

With a remote HTTP transport, we generally won't know about disconnect until we actually try to interact with it, which is when you try to issue commands. What kind of notification are you hoping for separate from that?

[AArnott]

Well, even if you don't realize connection loss till you try to transmit, at least an event would give us one common place to put our code to re-establish the connection.
Or perhaps alternatively, if there were a standard exception type we could catch around all use of the MCP server, we might put our recovery logic in our catch handler, such that we don't aggressively re-establish the connection just because it dropped, but rather only when we actually try to transmit to the server.

[stephentoub]

@AArnott, I realize your request was months ago and may no longer be needed, but does #1368 address the concern?