fix: align scalar extraction pattern with existing Title convention

Switch from GetPropertyValueFromNode(...) ?? X to the
if (!string.IsNullOrEmpty(...)) pattern used by the existing
Title/annotation extraction, for reviewer consistency.

Also add test for the allOf-based binding variant where $defs
sits inside allOf[0] and the nested schema has $ref +
$dynamicAnchor (the pattern from the blocker analysis).

Ref: #2895

Author: aqeelat

src/Microsoft.OpenApi/Models/JsonSchemaReference.cs

@@ -227,11 +227,35 @@ protected override void SetAdditional31MetadataFromMapNode(JsonObject jsonObject
 
         // JSON Schema 2020-12 keyword siblings ($defs is parsed separately in the deserializer
         // because it requires LoadSchema for nested schema materialization)
-        SchemaId = GetPropertyValueFromNode(jsonObject, OpenApiConstants.Id) ?? SchemaId;
-        Comment = GetPropertyValueFromNode(jsonObject, OpenApiConstants.Comment) ?? Comment;
-        DynamicRef = GetPropertyValueFromNode(jsonObject, OpenApiConstants.DynamicRef) ?? DynamicRef;
-        DynamicAnchor = GetPropertyValueFromNode(jsonObject, OpenApiConstants.DynamicAnchor) ?? DynamicAnchor;
-        Anchor = GetPropertyValueFromNode(jsonObject, OpenApiConstants.Anchor) ?? Anchor;
+        var id = GetPropertyValueFromNode(jsonObject, OpenApiConstants.Id);
+        if (!string.IsNullOrEmpty(id))
+        {
+            SchemaId = id;
+        }
+
+        var comment = GetPropertyValueFromNode(jsonObject, OpenApiConstants.Comment);
+        if (!string.IsNullOrEmpty(comment))
+        {
+            Comment = comment;
+        }
+
+        var dynamicRef = GetPropertyValueFromNode(jsonObject, OpenApiConstants.DynamicRef);
+        if (!string.IsNullOrEmpty(dynamicRef))
+        {
+            DynamicRef = dynamicRef;
+        }
+
+        var dynamicAnchor = GetPropertyValueFromNode(jsonObject, OpenApiConstants.DynamicAnchor);
+        if (!string.IsNullOrEmpty(dynamicAnchor))
+        {
+            DynamicAnchor = dynamicAnchor;
+        }
+
+        var anchor = GetPropertyValueFromNode(jsonObject, OpenApiConstants.Anchor);
+        if (!string.IsNullOrEmpty(anchor))
+        {
+            Anchor = anchor;
+        }
 
         if (jsonObject.TryGetPropertyValue(OpenApiConstants.Vocabulary, out var vocabNode) && vocabNode is JsonObject vocabObj)
         {

test/Microsoft.OpenApi.Readers.Tests/V31Tests/OpenApiSchemaTests.cs

@@ -1090,5 +1090,58 @@ public async Task ParseSchemaReferencePreservesVocabularySibling()
             referencing.Vocabulary["https://json-schema.org/draft/2020-12/vocab/core"].Should().BeTrue();
             referencing.Vocabulary["https://json-schema.org/draft/2020-12/vocab/applicator"].Should().BeFalse();
         }
+
+        [Fact]
+        public async Task ParseSchemaReferencePreservesDynamicAnchorInsideDefsInAllOf()
+        {
+            // Arrange — the allOf-based binding variant: $defs sits inside allOf[0],
+            // and the nested schema has $ref + $dynamicAnchor (the binding entry).
+            // This was called out as a real-world pattern that hits the same root cause
+            // because the inner schema is an OpenApiSchemaReference whose sibling was dropped.
+            var yaml = """
+                openapi: 3.1.0
+                info:
+                  title: allOf binding variant
+                  version: 1.0.0
+                paths: {}
+                components:
+                  schemas:
+                    Asset:
+                      type: object
+                      properties:
+                        id:
+                          type: string
+                    Paged:
+                      type: object
+                      properties:
+                        items:
+                          type: array
+                    AssetPaged:
+                      allOf:
+                        - $defs:
+                            contentType:
+                              $dynamicAnchor: contentType
+                              $ref: '#/components/schemas/Asset'
+                        - $ref: '#/components/schemas/Paged'
+                """;
+
+            // Act
+            using var stream = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(yaml));
+            var result = await OpenApiDocument.LoadAsync(stream, "yaml", SettingsFixture.ReaderSettings);
+            var assetPaged = result.Document.Components!.Schemas["AssetPaged"];
+
+            // Assert — the binding entry inside $defs/allOf[0] is reachable
+            // allOf[0] is a regular OpenApiSchema (no $ref at top level), so $defs is parsed normally.
+            // The nested contentType schema is an OpenApiSchemaReference ($ref: Asset),
+            // and its $dynamicAnchor sibling must be preserved.
+            assetPaged.AllOf.Should().NotBeNull();
+            assetPaged.AllOf!.Count.Should().Be(2);
+            var defsHolder = assetPaged.AllOf[0];
+            defsHolder.Definitions.Should().NotBeNull();
+            defsHolder.Definitions!.Should().ContainKey("contentType");
+            var contentType = defsHolder.Definitions["contentType"];
+            contentType.Should().BeOfType<OpenApiSchemaReference>();
+            contentType.DynamicAnchor.Should().Be("contentType");
+        }
     }
 }