0053: Implementer revision comparison

A device implementer needs to know whether an implementation satisfying the earlier model still satisfies the later model. This differs from whether a later implementation can replace an earlier one. Esdieff adds an explicit implementer perspective while retaining the client perspective of ADR 0039: Client-side revision comparison as the default.

For corresponding data descriptions, widened accepted inputs can require work from an existing implementation. Narrowed permitted outputs can invalidate its existing output. The existing bounded proof and witness machinery assesses these dual obligations with its comparison order reversed internally. Public revision labels, difference kinds, source origins, witness admissions, acknowledgements and version warnings retain chronological order. Unit and content-format added/removed reasons retain that order too.

The client-only exclusion of optional map entries absent from its earlier description does not apply to implementers. An open map’s newly unconstrained entry can widen accepted inputs, and a newly constrained entry can narrow permitted outputs. Both need ordinary whole-description witness checking.

This initial implementer perspective classifies data changes, established meaning changes and documentary changes. Endpoint presence, declaration requiredness, grouping counts, Property capabilities and whole Action/Event input or output additions and removals remain undetermined. Client rules for these changes cannot simply be reversed. In particular, an added optional affordance need not impose a new implementation obligation. Further structural rules need their own acceptance examples. Unknown meaning and exhausted limits keep their scoped undetermined results.

Context changes retain the interaction-only scope of ADR 0049: Context revision comparison. Neither perspective assesses metadata-consumer compatibility.

The library, direct CLI and saved Check plans select the same perspective. Every report records it, including an empty SARIF report. Comparison contract esdieff.revision-comparison/5 supersedes /4. Diff envelope 1.7 adds the required policy.perspective field to 1.6. Acknowledgement file format 1 is unchanged and does not bind entries to a perspective. Authors should export and review acknowledgements using the perspective they intend to assess.