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

PROJECT_KNOWLEDGE.md

@@ -92,6 +92,10 @@ validated work may specify another model explicitly.
 - Gold Standard tests are also a formal specification of meeting semantics.
 - Raw model responses should be preserved when diagnosing parser or truncation
   failures.
+- Responsibility attribution is a critical correctness invariant: people,
+  teams and departments must not be assigned ownership from discussion,
+  expertise, objection, thematic proximity, speaker adjacency, role guesses or
+  world knowledge. Assignment requires explicit evidence.
 
 ## Decision Taxonomy
 
@@ -108,6 +112,19 @@ Accepted decision semantics:
 - "No decision was reached" is different from "the group decided to defer the
   decision."
 
+## Responsibility Attribution
+
+Meeting Lab distinguishes mentioned people, speakers, participants,
+responsible people, departments, owners and assignees. These concepts must not
+be collapsed into one field.
+
+A `responsible` or future `owner` / `assignee` value may be recorded only when
+source evidence explicitly assigns, accepts or confirms responsibility. If the
+evidence is incomplete or ambiguous, the responsible person remains `null` or
+unset and the evidence is preserved. Future schema work may add
+`responsibility_status` values such as `explicit`, `accepted`, `proposed` and
+`unclear`, plus `attribution_evidence`.
+
 Current Prompt Version 2 decision baseline:
 
 - `decision_simple`: passing.