Microsoft just shipped something literally called the Agent Framework Harness, plus a "build your own agent harness" tutorial series. The harness is officially a product category now.

Their harness is the loop around the model: tools, memory, approvals, the plan/execute cycle. Necessary. And still single-player.

The part no SDK ships: where that loop runs and who can see it. A coding agent session your whole team can open, watch, and steer is a different layer entirely.

Disclosure: That is the layer we build at AQ (aq.dev): the multiplayer coding harness. Fun watching the vocabulary catch up.