fix(client): close stdio read sources during shutdown

[jstar0]

Summary

Fixes StdioClientTransport.close() so shutdown does not hang when the stdin read loop is blocked waiting for input.

Root Cause / Context

StdioClientTransport.closeResources() stopped the transport coroutine scope and then waited for the scope job to finish. On the JVM, a Source.readAtMostTo() call backed by a blocking Java stream does not necessarily return when the coroutine is cancelled. If the read loop stayed blocked, close() could wait indefinitely.

Changes

• Close the stdin source during stdio client shutdown before waiting for transport coroutines to finish.
• Also close the optional stderr source during shutdown.
• Keep source-close failures non-fatal and log them at debug level.
• Add a JVM regression test with a RawSource that blocks in readAtMostTo() until close() is called.
• Assert the close path completes, emits onClose, and does not invoke onError.

Scope / Risk

This is limited to StdioClientTransport shutdown behavior. It does not change the public API or server transports. The regression coverage is JVM-focused because the reported hang is caused by a blocking Java stream read.

Verification

./gradlew :integration-test:jvmTest --tests 'io.modelcontextprotocol.kotlin.sdk.client.StdioClientTransportTest'
./gradlew :kotlin-sdk-client:jvmTest
./gradlew :kotlin-sdk-client:ktlintCheck :integration-test:ktlintCheck :kotlin-sdk-client:detekt :integration-test:detekt :kotlin-sdk-client:apiCheck

Closes #514

[Copilot]

Pull request overview

Fixes a JVM shutdown hang in StdioClientTransport.close() by explicitly closing the read-side sources so a blocking readAtMostTo() can unblock and the transport’s coroutine scope can finish cleanly.

Changes:

• Close stdin Source during shutdown before waiting for transport coroutines to complete.
• Also close the optional stderr Source during shutdown; failures to close are non-fatal and logged at debug level.
• Add a JVM regression test using a RawSource that blocks in readAtMostTo() until close() is called, asserting close() completes and triggers onClose without onError.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
kotlin-sdk-client/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/client/StdioClientTransport.kt	Close stdin/stderr Sources during shutdown to prevent blocked read loops from hanging close().
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/StdioClientTransportTest.kt	Add JVM regression test covering blocked stdin read shutdown behavior.

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[devcrocod]

lgtm!