Create a network interface (port)

Creates a Network Interface in the active scope from the network interface creation form. The port reserves a fixed IP on the chosen subnet of the chosen network (automatic DHCP assignment or a manually pinned IPv4 address), receives an auto-generated MAC under the fa:16:3e OUI, and enters the build state; once provisioned it becomes down (unattached) or active. On acceptance the resource becomes discoverable in the scoped list. Optional allowedAddressPairs seeds VRRP/VIP IP+MAC entries (the UI "Add pair" flow); standard ports incur no charge and the fixed IP stays reserved until deletion. Validation: name must match ^[a-z0-9-]{1,60}$ (names are NOT unique: Neutron allows duplicate port names and every port operation addresses the port by id); description at most 255 characters; networkId must reference an accessible network and subnetName one of its subnets → ERR_NOT_FOUND when unknown; when ipAssignment=manual, fixedIp is required, must be a valid IPv4 inside the subnet CIDR, not the gateway or a DHCP-agent address, and not already allocated; securityGroups ids must resolve and are only enforced when portSecurity=true; each address pair ip must be a valid IPv4 or CIDR (its mac is optional — omitted or empty means the port's own MAC). Any violation → ERR_VALIDATION (422). Async & state: Asynchronous — 202 with an Operation record. Initial port state build → terminal down (created, unattached) or active; failure leaves no orphaned port. resource.updated SSE frames are emitted on the network-interface resource as the status patch (build → down/active) lands; the Operation transitions queued → running → succeeded|failed. Errors: 401 unauthenticated; 403 when the caller lacks contributor/admin rights on the scope; 404 when the referenced network, subnet or a security group does not exist in scope; 409 QUOTA_EXCEEDED when the port or fixed-IP quota for the subscription is exhausted; 422 on any field validation failure; 500 on provisioning-control failure. Idempotency/Concurrency: Idempotency-Key required; replaying the same key returns the original 202 Operation without creating a duplicate port.