Change the code. Keep the match.

Why it matters

• No minute-or-two reload. The usual loop is stop Play Mode, compile, reload the domain, press Play, replay your way back. On a mid-size project that's a minute or two, and an agent that writes five fixes pays it five times.
• The scene survives. Method bodies are patched into the running Mono domain, so objects and connections stay and the new code runs the next time the method is called.
• Four editors, one patch. The primary's hot-reload reaches every multiplayer clone, so you don't relaunch four players.
• Tune the live game. A jump curve changes in a match that never stopped, and an agent does the same: save the file, call its handle again.

It covers method bodies in Assembly-CSharp, your asmdefs and embedded packages, whether you edit in the editor or an agent writes to disk. Agents arm it with hotReload: true on unity.play, the same toggle the Player panel has. It needs Unity 6 on Mono.

For the rest of the live scene, unity.exec in the Unity MCP server runs C# in the session through Roslyn: spawn objects, change values, call your handles. In the clip above, two prompts recolor the lights and set the monolith spinning while Play Mode keeps running.