Platform keeps customization configuration; hosts execute it

Context

Platform handler tests do not substitute for host-owned production execution.

Decision

Keep customization declarations, handlers, bindings, preview resolution and invocation history in Platform. Hosts resolve and invoke through the shared library and save outcomes through the restricted invocation-writer role.

Alternatives Considered

Route every handler invocation through Platform. A central round trip would lengthen the host’s critical path and obscure its responsibility for failure.

Consequences

Single-answer points allow one authoritative binding within each scope.

Platform’s separate preview implementation can diverge from shared host resolution.

External event subscriptions belong to the integrations service; the withdrawn customization subscription facility is not revived.