Markitect schema-validation integration use case and fixture for Markdown proxy documents

docs/asset-registry-implementation.md

@@ -35,6 +35,8 @@ and SQLite repositories are adapters behind those ports.
 - `MetadataRecord` persistence with inferred/confirmed semantics preserved.
 - Custom metadata schema primitives with structured validation issues.
 - Metadata schema validation before asset create and metadata update writes.
+- Durable metadata schema registry and assignment rules for policy-selected
+  validation.
 - Actor and `OperationContext` required for material mutations.
 - Policy gateway authorization before asset mutations.
 - Fail-closed policy denial through `AuthorizationError`.
@@ -59,6 +61,8 @@ and SQLite repositories are adapters behind those ports.
 - `assets`
 - `representations`
 - `metadata_records`
+- `metadata_schemas`
+- `metadata_schema_assignments`
 - `context_entities`
 - `core_relationships`
 - `asset_versions`
@@ -72,7 +76,6 @@ idempotency key.
 
 ## Not Yet Implemented
 
-- Schema registry persistence and policy-assigned schema selection.
 - Standard metadata filtering beyond lifecycle and asset type.
 - Policy assignment storage and enterprise policy adapters.
 - Conflict detection beyond version-sequence uniqueness.
@@ -90,9 +93,10 @@ These remain in scope for later `KONT-WP-0005` tasks or adjacent workplans.
 - lifecycle denial with fail-closed policy and denied audit event,
 - SQLite reload preserving asset lifecycle, representation, metadata, versions,
   and audit history,
-- SQLite referential integrity for representation asset references.
+- SQLite referential integrity for representation asset references,
 - idempotent asset creation and conflicting idempotency-key reuse,
 - relationship creation with source-asset versioning and audit,
 - SQLite reload preserving context entities, relationships, and idempotency
   records,
-- custom metadata schema validation before registry writes.
+- custom metadata schema validation before registry writes,
+- persistent metadata schema registry and assignment reload behavior.