Agent Identity and Durable Workflows: The Two Problems MCP Can't Solve

MCP 2026-07-28 dropped sessions. The initialize handshake is gone. The Mcp-Session-Id header is gone from Streamable HTTP. Protocol version, client info, and capabilities now travel in a _meta field on every request, so any instance can serve any call. The protocol is cleaner for it. This is the largest revision since launch, and it leaves both of the questions that block enterprise agent deployments exactly where they were. MCP standardizes how a model reaches a tool. Neither question lives inside that scope, and no future revision is likely to put them there: Who is the agent acting as, and what is it allowed to do? What happens when a process takes three days and the model context is gone? The spoiler: on AWS the parts already exist. Policy in AgentCore evaluates every Gateway call in Cedar against a principal, an action, and a resource, and writes the allow or deny to an audit log. Temporal policies, added in August 2026, extend that across an agent's trajectory, including human approval ahead of a privileged action. AgentCore Identity distributes the credentials. Step Functions holds anything measured in days. The remaining work is composition: deciding which principal each agent acts as, and what it may commit to. No service ships that decision. What the stateless redesign actually solved The stateless redesign removes real pain. Long-held SSE connections forced sticky routing, which pushed teams into shared session stores and gateway packet inspection just to scale horizontally. The new model provisions for request rate instead of concurrent users. A round-robin load balancer is now enough. Lambda, Cloud Run, and Workers become viable backends. Multi Round-Trip Requests (SEP-2322) handle elicitation without a held connection. The server returns an InputRequiredResult carrying what it still needs plus an opaque requestState blob. The client collects the answers and re-issues the same call with inputResponses and the echoed state. Any instance picks up the retr