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

ROADMAP.md

@@ -126,6 +126,67 @@ Out of scope:
 - Export formats beyond those needed to validate the model.
 - Knowledge-system storage design.
 
+## Phase 4A - Meeting Context V2 and Entity Registry
+
+Goal:
+
+- Replace primarily manual Meeting Context authoring with an interactive
+  entity confirmation workflow backed by a persistent Entity Registry.
+
+Accepted architecture:
+
+```text
+Whisper
+    ↓
+Entity Detection
+    ↓
+User Confirmation
+    ↓
+Entity Registry Update
+    ↓
+Meeting Context Builder
+    ↓
+meeting_context.yaml
+    ↓
+Extraction Pipeline
+```
+
+Deliverables:
+
+- Persistent Entity Registry independent from individual meetings as the
+  cross-meeting knowledge source for confirmed entities, aliases and
+  organizational metadata.
+- Stable internal entity IDs for people, organizations, departments, products,
+  projects, locations and abbreviations.
+- First-class aliases, including spelling and transcription variants.
+- User confirmation UI/workflow for unknown names.
+- Meeting Context Builder that produces meeting-specific `meeting_context.yaml`
+  from registry entries, user confirmations and meeting metadata.
+- Generated `meeting_context.yaml` as the authoritative meeting-specific Point
+  of Truth and reproducible input artifact for each meeting run.
+- Similarity suggestions for spelling variants, Whisper variants, umlaut
+  handling and OCR-like mistakes.
+
+Prerequisites:
+
+- Agreement on the Entity Registry data model.
+- Review workflow for confirming unknown entities after Whisper transcription.
+- Meeting Context V1 remains the extraction interface until V2 is implemented.
+
+Current status:
+
+- Accepted Architecture.
+- Implementation deferred.
+
+Out of scope:
+
+- Autonomous learning.
+- Silent registry updates.
+- Registry overrides of explicit meeting-specific confirmations.
+- Silent changes to historical Meeting Context after Registry updates.
+- Inferring responsibility, decisions, ownership or attendance from registry
+  metadata.
+
 ## Phase 5 - Output Views
 
 Goal: