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

examples/markitect-tool-contract/schemas/adr-proxy.schema.md

@@ -0,0 +1,38 @@
+---
+schema-id: "kontextual-engine.markdown-proxy.adr.v1"
+version: "1.0.0"
+status: "example"
+---
+
+# ADR Proxy Document Schema
+
+```json
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "title": "ADR Proxy Document",
+  "type": "object",
+  "required": ["frontmatter", "headings"],
+  "properties": {
+    "frontmatter": {
+      "type": "object",
+      "required": ["document_type", "status", "owner"],
+      "properties": {
+        "document_type": {"const": "adr"},
+        "status": {"enum": ["proposed", "accepted", "deprecated", "superseded"]},
+        "owner": {"type": "string", "minLength": 1}
+      }
+    },
+    "headings": {
+      "type": "array",
+      "minItems": 3,
+      "contains": {
+        "type": "object",
+        "required": ["text"],
+        "properties": {
+          "text": {"const": "Decision"}
+        }
+      }
+    }
+  }
+}
+```