Decide who owns each fact, what an event means, and how an uncertain result is resolved before moving data.
Choose the owner of the fact.
An accounting system may own the posted invoice while Helix owns receipt and inspection evidence. Decide which system creates each record, which identifier links the two, and how a correction travels. Without this agreement, two apparently successful integrations can keep overwriting each other.
Map meaning as well as fields. “Approved,” “released,” and “posted” may describe different decisions. A shared text label does not prove the underlying lifecycle states are equivalent.
Use each interface for the right job.
An API supports explicit requests and controlled actions. A webhook announces a change that another service can react to. MCP makes selected resources and tools accessible to an AI client. These surfaces can share the same underlying authority rules while serving different callers.
Avoid using a generic record update to simulate an operational command. Receiving stock or approving a result may need prerequisites, permission checks, side effects, and evidence that a simple field mutation cannot represent.
Design for delivery uncertainty.
A message may arrive more than once. A caller may time out after the server has already committed its action. Persist a stable identity for the request or event, and design the receiver to recognize repeats.
Where a webhook acts as a notification, retrieve authoritative current state before a consequential next step. Define retry, reconciliation, and operator recovery behavior. A visible queue of unresolved items is more useful than silent divergence.
Test the agreement end to end.
Run a normal path, a duplicate, an out-of-order notification, an authorization failure, and a timeout after commit. Follow the result into both systems and their audit histories.
Before production, document the owner of reconciliation and the action taken when the integration is unavailable. The connection is complete when people can explain and recover its behavior, not merely when the first request returns successfully.
- Name the authoritative system for each business fact.
- Map states and commands, not only fields.
- Verify duplicate delivery, timeouts, and reconciliation.
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