Multi-agent calendar collision.

A multi-agent calendar collision is the failure mode that occurs when two or more independent scheduling agents — operated by different vendors, principals, or processes — each commit a booking to the same calendar slot without coordinating with one another. The underlying calendar API accepts both writes because it has no notion of "the other agent that was about to write here," and the human ends up with overlapping events that each system believes is canonical.

• Multi-agent scheduling collision
• Multi-agent booking collision
• Agent-vs-agent calendar race
• "Logic collision" (industry-press framing, 2026)

Calendar APIs were designed for one writer at a time. None of the consumer or enterprise calendar APIs in production today expose a compare-and-swap primitive at the slot level. An agent's "check availability" and an agent's "commit booking" are two separate network calls, and other agents can complete their own check-and-write between them. The collision is the predictable consequence of two rational systems operating on a shared resource without a coordination layer between them.

1. Hold-vs-hold. Two agents place a tentative hold on the same slot; both ask the human to confirm.
2. Hold-vs-commit-inside-bump. One agent holds; another commits seconds later; the calendar reflects whichever wrote last.
3. Commit-vs-frozen. Both agents commit successfully and the calendar accepts both events.
4. External-event-overlap. The human types a manual event over an agent's hold; the agent learns about it only on its next poll.

Each pattern is illustrated with timing diagrams in the agents-collide post.

• Cal.com and Calendly are the gateway through which agents reach calendars. They check availability at booking time but do not coordinate between multiple racing agents — their AI-agents documentation recommends best-effort slot-checking by the agent itself (cal.com/docs/agents).
• Motion, Reclaim, and Clockwise are single-user AI calendar planners. They solve "the human can't decide what to focus on" — not "two agents are racing." Two of them installed on the same calendar collide.
• Academic prior art such as ScheduleMe (arxiv 2509.25693) addresses internal coordination inside a single multi-agent system, not cross-principal arbitration.
• MCP servers for calendars are a transport for exposing tools to agents — not a coordination protocol. An agent connected over MCP races against any other agent doing the same.

1. Atomic compare-and-swap at the slot level. Check and write are one indivisible operation, enforced at the storage layer.
2. Explicit priority, configured by the calendar owner. Conflicts resolve to a deterministic winner by a per-user policy.
3. An append-only audit log readable by both parties. Every collision has an answer; both winning and losing agents can read it.

• What is a multi-agent calendar collision? — extended FAQ.
• Why AI scheduling agents collide — the longer narrative manifesto.
• How a deterministic conflict engine resolves 8,217 collisions — engine-level implementation.
• The protocol spec — the wire surface of a coordination layer.