Multiple Sessions or Multi-Agent? I ran 27 agents to answer that
An orchestration study with real experiments: 6 probes to pin down where a subagent's isolation boundary sits, and 13 agents building the same game three different ways, each build verified in a headless browser. The counterintuitive result — multi-agent buys width inside one task, multiple sessions buy length across time and total context; they're orthogonal axes. What actually decides whether parallel development works is an interface contract everyone follows (without one, 2 of 5 assemblies went straight to a blank screen).