API Gateway WebSocket body parameters not mapped to integration headers

When configuring API Gateway WebSocket integrations with request parameter mappings like 'integration.request.header.someHeaderParam'='route.request.body.someBodyParam', LocalStack sends the literal parameter path string (e.g., 'route.request.body.someBodyParam') to backend integrations instead of extracting and mapping the actual value from the WebSocket message body. Built-in context values like context.connectionId work correctly, but custom body parameters fail to resolve.

Update LocalStack Pro to latest version (after 2025-03-07). Pull the localstack/localstack-pro:latest Docker image which contains the fix. The corrected implementation works whether or not APIGW_ENABLE_NEXT_GEN_WEBSOCKETS=1 is set. Verify by checking LocalStack logs for the actual parameter values (not literal path strings) being sent to integration endpoints.