BedrockAgentCoreApp crashes with UnicodeDecodeError when session id contains non-ASCII characters

[jesseturner21]

Description

When invoking an agent with a session id containing non-ASCII characters (e.g. sesión-123), the runtime crashes with a UnicodeDecodeError instead of returning a validation error.

Steps to reproduce

1. Create a minimal app with BedrockAgentCoreApp and a single @app.entrypoint.
2. Invoke it with header X-Amzn-Bedrock-AgentCore-Runtime-Session-Id: sesión-123.
3. The request fails with a 500 and the traceback below.

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 3: ordinal not in range(128)

Expected behavior

Either the session id is accepted, or a 400 with a clear validation message is returned.

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Note: test issue filed by @jesseturner21 to validate the issue auto-triage workflow; will be closed after verification.

[jesseturner21]

Triager verified working (correctly labeled this test issue as 'bug') — closing.