necro-posting here, but that's kinda what we're working on! We're focused on creating cloud workspaces for sandboxed coding agents and it's built to support any agent harness. https://www.amika.dev/
I've been using the OpenAI Agents SDK for a while now and am largely happy with the abstractions - handoffs/sub-agents, tools, guardrails, structured output, etc. Building the infra and observability, and having it scale reliably, was a bigger pain for me. So I do get Anthropic's move into managed agents.
Framework is simply way too rigid for a non-deterministic technology.
We may see libraries that provide tools for managing agents, but then again, there's nothing that tmux can't do already.