Tasks PR resulting in random crashes of test host

[stephentoub]

The active Test Run was aborted because the host process exited unexpectedly. Please inspect the call stack above, if available, to get more information about where the exception originated from.
The test running when the crash occurred: 
ModelContextProtocol.AspNetCore.Tests.StreamableHttpServerConformanceTests.DeleteRequest_CompletesSession_WhichCancelsLongRunningToolCalls

[stephentoub]

Another similar crash but in a different test:
https://github.com/modelcontextprotocol/csharp-sdk/actions/runs/21459259520/job/61817397132?pr=1191

The active Test Run was aborted because the host process exited unexpectedly. Please inspect the call stack above, if available, to get more information about where the exception originated from.
The test running when the crash occurred: 
ModelContextProtocol.AspNetCore.Tests.StreamableHttpServerConformanceTests.GetRequest_Receives_UnsolicitedNotifications

This test may, or may not be the source of the crash.

I only saw these after the Tasks PR was merged. I suspect that's actually the root cause.

[ericstj]

One of the failures I looked at in https://github.com/modelcontextprotocol/csharp-sdk/actions/runs/21459259520/job/61817397132?pr=1191 was a hang on linux.

Here's the hang that was in that dump - https://gist.github.com/ericstj/e4bd3a3dc79dc42a4576f06908e653fc