fix(python-backend): Fix Nova Sonic protocol and SDK v0.1.0 compatibi…

[jimini55]

…lity

• Add role: USER to audio content blocks (required by Nova Sonic)
• Fix response processing timing to start after setup
• Validate first content has SYSTEM role
• Upgrade to aws-sdk-bedrock-runtime v0.1.0
• Update imports to smithy_aws_core.identity module
• Use auth_schemes with SigV4AuthScheme(service=bedrock)
• Reduce logging verbosity (warn only on true silence)

Issue #, if available:

• Nova Sonic Protocol Implementation Issues in Python WebSocket Server #240
• Breaking Change in aws-sdk-bedrock-runtime v0.1.0: SigV4 Authentication Parameter Mismatch #241

Description of changes:

This PR fixes two critical issues preventing the Python backend from working with Amazon Nova Sonic:

1. Nova Sonic Protocol Implementation Issues

• Added required "role": "USER" field to audio content blocks - Nova Sonic requires explicit role specification
• Fixed response processing timing by moving task creation to after session setup (prevents race condition)
• Added validation ensuring first content block has "role": "SYSTEM" (Nova Sonic protocol requirement)
• Enhanced audio validation to detect and log silent audio (helps diagnose frontend issues)
• Reduced log verbosity to warn only on completely silent audio (amplitude = 0) instead of low audio

2. AWS SDK Breaking Changes (v0.1.0)

• Upgraded from aws-sdk-bedrock-runtime==0.0.2 to 0.1.0 (released Sept 29, 2025)
• Fixed imports: credential resolvers moved from smithy_aws_core.credentials_resolvers.* to smithy_aws_core.identity.*
• Updated Config API: replaced http_auth_schemes with auth_schemes parameter
• Updated SigV4AuthScheme to require service="bedrock" parameter
• Maintained secure ContainerCredentialsResolver for ECS deployment

Testing:

• ✅ Tested locally with test script
• ✅ Deployed to ECS and verified working
• ✅ Confirmed Nova Sonic responds to audio input and generates speech output

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