Don't log named pipe connection failures as errors in BuildServerConnection

[Copilot]

When connecting to the compiler server fails due to a timeout, pipe ownership mismatch, or other exception, the previous LogException/LogError calls emitted messages prefixed with "Error Error:" or "Error:". This matches the canonical error pattern that MSBuild's Exec task detects in process output, causing it to surface a build error — even though these are transient, recoverable conditions where the compiler falls back gracefully to the command-line tool.

Change

In BuildServerConnection.cs, replace LogException/LogError with plain Log for all three recoverable failure paths in TryConnectToServerAsync. Key diagnostic info (exception type + message) is retained; only the "Error:" prefix is dropped.

- logger.LogException(e, $"Connecting to server timed out after {timeoutMs} ms");
+ logger.Log($"Connecting to server timed out after {timeoutMs} ms: '{e.GetType().Name}' '{e.Message}'");

- logger.LogError("Owner of named pipe is incorrect");
+ logger.Log("Owner of named pipe is incorrect");

- logger.LogException(e, "Exception while connecting to process");
+ logger.Log($"Exception while connecting to process: '{e.GetType().Name}' '{e.Message}'");

LogException/LogError are appropriate for unexpected failures. These connection failures are all handled, recoverable conditions — logging them as errors was misleading.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Error Error: 'IOException' 'The semaphore timeout period has expired reported but not really an issue</issue_title>
<issue_description>10.0.103:

During building with Visual Studio 2026 18.3.0 we encounter the following:

EXEC(0,0): Error Error: 'IOException' 'The semaphore timeout period has expired.

It appears that this error is reported, but the build is not failing as a retry is done, but as the error is reported as a canonical error format the exec msbuild task https://learn.microsoft.com/en-us/visualstudio/msbuild/exec-task?view=visualstudio reports an error and stops.

But as this is not really an error as dotnet build is not stopping can the following line be adapted that, it does not report an canonical error

https://github.com/dotnet/roslyn/blob/main/src/Compilers/Shared/BuildServerConnection.cs#L415

</issue_description>

Comments on the Issue (you are @copilot in this section)

@jjonescz > the exec msbuild task https://learn.microsoft.com/en-us/visualstudio/msbuild/exec-task?view=visualstudio reports an error and stops.

I'm not sure what do you mean by this. Where exactly is this Exec task being used? There shouldn't be any Exec task used during normal dotnet build when invoking the C# compiler.</comment_new>

• Fixes Error Error: 'IOException' 'The semaphore timeout period has expired reported but not really an issue #82583

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[jjonescz]

@copilot