Routing pattern not included in /message endpoint when using SSE Server

[anibal-acosta]

When you set a routing pattern like ...

app.MapMcp("mymcpserver")

The endpoint works with /mymcpserver/sse but this return

event: endpoint
data: /message?sessionId=XXX

should be

event: endpoint
data: {routing_pattern}/message?sessionId=XXX

In my example should be

event: endpoint
data: /mymcpserver/message?sessionId=XXX

[halter73]

@anibal-acosta Should we close this issue now that we emit root-relative message endpoint URLs as of #323? As I noted on the PR, I'm not sure we even need to emit a root-relative URL now that the sse endpoint always ends in /sse.

I do wonder if this change is necessary now that MapMcp only routes SSE requests to $"{groupPrefix}/sse" and not just $"{groupPrefix)" since that's now used for the "Streamable HTTP" transport". After all, "messages" should be a valid relative reference.

Regarding this,

The endpoint works with /mymcpserver/sse but this return

event: endpoint
data: /message?sessionId=XXX

As of preview.9 which included the changes in #291 (preview.10 is currently on nuget.org), the endpoint was emitted as follows without the root-relative "/" prefix so it should be a normal root-relative URL which should work with any endpoint ending in "/sse" :

event: endpoint
data: message?sessionId=XXX

I wonder if we should just go back to that behavior instead of using the root-relative URL since it's simpler.