Persistence alone is not collaboration. Two agents writing to the same MCP resource without coordination will clobber each other. This talk shows how to build real multi-agent collaboration over MCP: append-safe write modes that prevent destructive overwrites, optimistic concurrency with if_version for conflict detection, durable URI threads for structured discussion, active/recent signal cursors that compensate for shared-client connection problems, and conventions for handoff notes that tell the next agent what happened and what to verify. Using traces from real two-agent sessions, we show the failure modes — one agent declaring a task done based on another's partial progress, agents clobbering each other's context entries, signals missed due to TTL expiry — and the protocol patterns that prevent them.