Export agent for runtime

Export a fully-resolved, self-contained agent definition that the @runtypelabs/runtime package can consume directly at boot. Capabilities, flows, and nested sub-agents are inlined recursively (up to 3 levels). MCP credential values and external-agent auth credentials are replaced with secret-name references. The response carries `hostDependencies`: the runtime seams the exported artifact needs a host to wire before it can run everything it describes. A durable-class step (`wait-until` or `crawl`) anywhere in the agent's executable closure declares a `durable-pause-host` dependency; a detached-capable dynamic subagent pool or a detached inline subagent tool declares a `background-run-coordinator` dependency. The array is empty when nothing needs wiring.