if the goal is OSS over closed platform, why not try open code + bitrouter (https://github.com/bitrouter/bitrouter)

full disclosure, this is my own project but I truly think it would be a potential fit of what you're looking for:)

OpenCode is a great replacement harness…I use it with deepseek v4 and it is as good as Claude without it trying to sneak in Anthropic specific code