Java SDK: Reject byte arrays instead of letting the task hang

[FrankYang0529]

Why

• A Java task that pushes a byte[], for example with client.setXCom("payload", bytes), never finishes. The SDK packed the array as msgpack bin, but the supervisor only accepts JSON values. The supervisor logs Unable to decode message and never replies, so the task waits forever.

How

• packAny throws IllegalArgumentException for a ByteArray before anything is written to the socket. The exception message asks the task author to encode the bytes as a string.

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Was generative AI tooling used to co-author this PR?

• Yes - Claude Code

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