SupplyChainNode.hp: payment responsibility references the preceding hp=1 node

[fgranata]

The hp description states that when hp=1, the seller in sid is "responsible for paying the previous node in the chain." With SupplyChain 1.1, an hp=0 node can precede the first payment node — the Supply Chain Validation Implementation Guidance notes implementers should expect one or more hp=0 nodes in front of the first payment handling node — and in that arrangement the previous node is not paid by the seller, so the description is incorrect as written.

The Implementation Guidance validation methods (section 4.6) already use the correct formulation: the payment linkage runs between hp=1 nodes ("should match the advertising system in the preceding hp=1 node"). This change aligns the field description to it and adds that hp=0 nodes are not part of the payment linkage. For version 1.0 chains, where all nodes are payment handling, the preceding hp=1 node is the previous node, so nothing changes.

Part of the public comment feedback for InteractiveAdvertisingBureau/Supply-Chain-Validation#1.

[simontrasler]

Please make the equivalent edits to openrtb.proto to keep the two files in sync.

[fgranata]

Done — mirrored the change in proto/src/main/com/iabtechlab/openrtb/v2/openrtb.proto (the hp field comment on SupplyChainNode), same wording as 2.6.md. The surrounding note that hp should always be 1 for version 1.0 is untouched.