nfs-share and smb-share share an intent, not a contract; one seat would be
a union with every field optional. What the exemplar exposes is that a
seat declared inside one module cannot be implemented by another without
depending on it.
The operator's call: a node-scoped system seat family (node-nfs-share,
node-smb-share, …) defined by the control plane, one per protocol as
package registries are (ADR 0109), so several modules occupy it and a
machine may hold both.
ace exports the operator's media library over NFS and Samba with host
services no module declares: they close at converge, nothing owns their
configuration, and no module elsewhere can require the share. Proposes a
file-sharing module that accesses the paths, holds a node-scoped seat it
defines, and provides file-share to consumers.