Document validation architecture and renderer faithfulness findings

- document Entity Registry and Meeting Context V2 architecture
- preserve meeting_context.yaml as the authoritative meeting-specific input
- define immutable authoritative metadata across all pipeline stages
- restrict Constraint Repair to deterministic structured-data operations
- record BUG-003 root cause and deferred entity-verification resolution
- document BUG-005 attendance-consistency design
- add BUG-006 renderer faithfulness root-cause analysis
- distinguish Engineering Readiness from Practical Usability
- update the persistent regression bug tracker

docs/data-models.md

@@ -266,6 +266,90 @@ renderer integration remains planned.
 
 ---
 
+# Entity Registry
+
+Accepted Architecture. Implementation deferred.
+
+The Entity Registry is the persistent cross-meeting knowledge source for
+confirmed entities, aliases and organizational metadata. It is independent from
+individual meetings and is the planned long-term source used to prepare Meeting
+Context V2.
+
+Entity types include:
+
+- people
+- organizations
+- departments
+- products
+- projects
+- locations
+- abbreviations
+
+Each entity has a stable internal identifier. The displayed name may change
+over time, but the internal identifier must remain stable.
+
+Conceptual shape:
+
+```json
+{
+    "entity_id": "person_0001",
+    "entity_type": "person",
+    "display_name": "Jovana",
+    "aliases": [
+        "Jovana",
+        "Giovanna",
+        "Jovanna",
+        "Giovana"
+    ],
+    "status": "confirmed"
+}
+```
+
+The registry never learns automatically. It may propose matches, but only
+confirmed user actions update it. Similarity search may suggest spelling
+variants, Whisper transcription variants, umlaut variants or OCR-like mistakes,
+but suggestions require explicit confirmation.
+
+Previously unseen names should be classified by the user as one of:
+
+- meeting participant
+- mentioned person
+- external person
+- transcription error
+- ignore
+
+The Entity Registry must not infer responsibility, decisions, attendance or
+ownership.
+
+---
+
+# Meeting Context V2
+
+Accepted Architecture. Implementation deferred.
+
+Meeting Context V2 is an authoritative meeting-specific YAML Point of Truth
+generated or assisted from:
+
+- Entity Registry
+- user confirmations
+- meeting metadata
+
+The YAML remains the extraction pipeline interface and the authoritative
+meeting-specific Point of Truth for that meeting run. It is also a reproducible
+input artifact: changes to the Entity Registry after a meeting run must not
+silently change the historical Meeting Context used for that run.
+
+The Entity Registry remains the persistent cross-meeting knowledge source. It
+must not override explicit meeting-specific confirmations.
+
+Meeting Context V2 should reduce manual work, improve alias handling, detect
+transcription errors earlier and make Meeting Context quality scalable across
+many meetings.
+
+See `docs/adr-meeting-context-v2-entity-registry.md`.
+
+---
+
 # Topic Result
 
 After extraction, every topic contains the collected information.