Bedrock AgentCore runtime V2 flattens cold starts to a P75 of about 2 seconds regardless of image size

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AWS shipped a new AgentCore runtime on 18 September, opted into with platformVersion=V2, that holds P75 cold start near 2 seconds for images from 200MB to 2GB. The old runtime ranged from 5.4 to nearly 30 seconds as image size grew. The new runtime also reclaims memory when a session goes cold instead of billing peak memory for the session's life, charging a higher rate against far fewer GB-hours, which cuts bills for bursty agents that spike then idle.