Flaky test: StdioServerTransport.DisposeAsync() can hang

[halter73]

The active test run was aborted. Reason: Test host process crashed
Data collector 'Blame' message: The specified inactivity time of 7 minutes has elapsed. Collecting hang dumps from testhost and its child processes.

Test Run Aborted.
Total tests: Unknown
     Passed: 189
    Skipped: 3
 Total time: 7.6249 Minutes
Results File: /home/runner/work/csharp-sdk/csharp-sdk/testresults/_fv-az[221](https://github.com/modelcontextprotocol/csharp-sdk/actions/runs/14150315138/job/39642597376?pr=142#step:10:222)0-804_2025-03-29_23_16_37.trx

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.Tests.Transport.StdioServerTransportTests.Constructor_Should_Initialize_With_Valid_Parameters

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

https://github.com/modelcontextprotocol/csharp-sdk/actions/runs/14150315138/job/39642597376?pr=142

I think there's good reason to believe StdioServerTransportTests.Constructor_Should_Initialize_With_Valid_Parameters is the source of the hang considering Constructor_Should_Initialize_With_Valid_Parameters is the only in-proc test that tries to read from the real stdin and then cancel the read gracefully. I'm pretty sure we're cancelling the ReadLineAsync operation correctly, so we might have to look into the Unix ConsolePal.

[eiriktsarpalis]

Updated the title to reflect that this hands on Windows as well: #160 (comment)

[halter73]

Thanks. I was just about to do the same thing. More context:

• Canceling read from stdin in StdioServerTransport.DisposeAsync is also flaky on Windows
• https://github.com/modelcontextprotocol/csharp-sdk/actions/runs/14161333333/job/39667212874