Enforce explicit responsibility attribution

- document responsibility attribution as a project-wide invariant
- prevent inferred ownership in protocol rendering
- add negative gold regression for false responsibility assignment
- document future responsibility evidence and attribution model
- record the real-life benchmark finding

docs/data-models.md

@@ -272,6 +272,27 @@ Each item contains at least:
 Action items also preserve deterministic fields such as `responsible` and
 `deadline` when present.
 
+Responsibility attribution is stricter than mention or participation. A
+`responsible` value may be kept only when source evidence explicitly assigns,
+accepts or confirms responsibility. If evidence is incomplete, ambiguous or
+only based on a suggestion, objection, topic expertise or department mention,
+the field remains `null` or unset and the evidence is preserved.
+
+Do not collapse these concepts into one field:
+
+- `speaker`: person who uttered the evidence.
+- `mentioned_person`: person named in the evidence.
+- `participant`: person present in the meeting.
+- `responsible_person`: person explicitly assigned to or accepting an action.
+- `department`: organizational unit discussed or represented.
+- `owner`: durable ownership of a process, system or knowledge object.
+- `assignee`: operational person or team assigned to a concrete task.
+
+Future compatible fields may include:
+
+- `responsibility_status`: `explicit`, `accepted`, `proposed` or `unclear`.
+- `attribution_evidence`: source evidence supporting the assignment status.
+
 Example:
 
 ```json