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Cole-Greer pushed a commit to branch simplePDT
in repository https://gitbox.apache.org/repos/asf/tinkerpop.git

commit c77d1d694e8beed17281cf74a4bbd5bda66ad171
Author: Cole Greer <[email protected]>
AuthorDate: Wed Jun 24 13:25:43 2026 -0700

    Add PrimitivePDTAdapter, registry hydration, and binary reader/writer 
dispatch
    
    Wires PrimitivePDT into the registry and the GraphBinary read/write paths.
    
    - New PrimitivePDTAdapter<T> extends ProviderDefinedTypeAdapter<T> with
      toValue(T)/fromValue(String).
    - ProviderDefinedTypeRegistry: parallel primitiveAdaptersByName/ByClass;
      register(...) routes PrimitivePDTAdapter into the primitive maps;
      getPrimitiveAdapterByName/ByClass added. Registering a class already
      registered under the other kind (composite vs primitive) throws
      (fail-fast, bidirectional). ServiceLoader discovery on the supertype
      picks up primitive adapters automatically.
    - hydratePrimitive(PrimitiveProviderDefinedType): adapter lookup by name +
      fromValue, with graceful degradation (log + return raw) on missing or
      throwing adapter. The composite hydrate() recursion now also hydrates a
      PrimitiveProviderDefinedType nested inside a composite's fields.
    - GraphBinaryReader.read(): hydrate a deserialized 
PrimitiveProviderDefinedType
      via the registry.
    - GraphBinaryWriter: dehydrate a raw object whose class has a registered
      PrimitivePDTAdapter into a PrimitiveProviderDefinedType (parallel to the
      composite adapter path), resolving the PRIMITIVE_PDT serializer.
    
    GraphSON, grammar, server fixtures, and GLVs remain for later beads.
    
    Tests: registry primitive register/lookup, hydratePrimitive success and
    graceful degradation, dual-registration throws, 
primitive-nested-in-composite
    hydration; writer adapter round-trip for an unannotated primitive type.
    
    tinkerpop-2gy.3
    
    Assisted-by: Kiro:claude-opus-4.8
---
 .../structure/io/binary/GraphBinaryReader.java     |   4 +
 .../structure/io/binary/GraphBinaryWriter.java     |  38 ++++--
 .../structure/io/pdt/PrimitivePDTAdapter.java      |  28 ++++
 .../io/pdt/ProviderDefinedTypeRegistry.java        |  52 +++++++-
 .../io/pdt/ProviderDefinedTypeRegistryTest.java    | 141 +++++++++++++++++++++
 .../util/ser/binary/GraphBinaryWriterPdtTest.java  |  75 +++++++++++
 6 files changed, 327 insertions(+), 11 deletions(-)

diff --git 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryReader.java
 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryReader.java
index 5f3cf240c6..157bea16b9 100644
--- 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryReader.java
+++ 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryReader.java
@@ -19,6 +19,7 @@
 package org.apache.tinkerpop.gremlin.structure.io.binary;
 
 import org.apache.tinkerpop.gremlin.structure.io.Buffer;
+import 
org.apache.tinkerpop.gremlin.structure.io.pdt.PrimitiveProviderDefinedType;
 import org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedType;
 import 
org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedTypeRegistry;
 
@@ -108,6 +109,9 @@ public class GraphBinaryReader {
         if (pdtRegistry != null && result instanceof ProviderDefinedType) {
             return (T) pdtRegistry.hydrate((ProviderDefinedType) result);
         }
+        if (pdtRegistry != null && result instanceof 
PrimitiveProviderDefinedType) {
+            return (T) 
pdtRegistry.hydratePrimitive((PrimitiveProviderDefinedType) result);
+        }
         return result;
     }
 }
diff --git 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryWriter.java
 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryWriter.java
index 27bc0bda15..7bbdb6d0f6 100644
--- 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryWriter.java
+++ 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/binary/GraphBinaryWriter.java
@@ -18,9 +18,12 @@
  */
 package org.apache.tinkerpop.gremlin.structure.io.binary;
 
+import 
org.apache.tinkerpop.gremlin.structure.io.binary.types.PrimitiveProviderDefinedTypeSerializer;
 import 
org.apache.tinkerpop.gremlin.structure.io.binary.types.ProviderDefinedTypeSerializer;
 import 
org.apache.tinkerpop.gremlin.structure.io.binary.types.TransformSerializer;
 import org.apache.tinkerpop.gremlin.structure.io.pdt.CompositePDTAdapter;
+import org.apache.tinkerpop.gremlin.structure.io.pdt.PrimitivePDTAdapter;
+import 
org.apache.tinkerpop.gremlin.structure.io.pdt.PrimitiveProviderDefinedType;
 import org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedType;
 import 
org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedTypeAdapter;
 import 
org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedTypeRegistry;
@@ -91,6 +94,10 @@ public class GraphBinaryWriter {
             serializer.writeValue((T) dehydrateToPdt(value, objectClass), 
buffer, this, nullable);
             return;
         }
+        if (serializer instanceof PrimitiveProviderDefinedTypeSerializer && 
!(value instanceof PrimitiveProviderDefinedType)) {
+            serializer.writeValue((T) dehydrateToPrimitivePdt(value, 
objectClass), buffer, this, nullable);
+            return;
+        }
         serializer.writeValue(value, buffer, this, nullable);
     }
 
@@ -108,16 +115,16 @@ public class GraphBinaryWriter {
         final TypeSerializer<T> serializer = (TypeSerializer<T>) 
getSerializerOrAdapterFallback(objectClass);
 
         if (serializer instanceof ProviderDefinedTypeSerializer && !(value 
instanceof ProviderDefinedType)) {
-            // Convert to ProviderDefinedType (via annotation or adapter), 
then re-enter write().
-            // On re-entry, ProviderDefinedType.class is directly registered 
in the registry,
-            // and the instanceof guard prevents double-wrapping.
             write((T) dehydrateToPdt(value, objectClass), buffer);
             return;
         }
 
+        if (serializer instanceof PrimitiveProviderDefinedTypeSerializer && 
!(value instanceof PrimitiveProviderDefinedType)) {
+            write((T) dehydrateToPrimitivePdt(value, objectClass), buffer);
+            return;
+        }
+
         if (serializer instanceof TransformSerializer) {
-            // For historical reasons, there are types that need to be 
transformed into another type
-            // before serialization, e.g., Map.Entry
             final TransformSerializer<T> transformSerializer = 
(TransformSerializer<T>) serializer;
             write(transformSerializer.transform(value), buffer);
             return;
@@ -168,15 +175,20 @@ public class GraphBinaryWriter {
 
     /**
      * Attempts to get a serializer for the given class. If no serializer is 
found and the pdtRegistry
-     * has an adapter for the class, returns the CompositePDT serializer.
+     * has an adapter for the class (composite or primitive), returns the 
appropriate PDT serializer.
      */
     @SuppressWarnings("unchecked")
     private <DT> TypeSerializer<DT> getSerializerOrAdapterFallback(final 
Class<?> type) throws IOException {
         try {
             return (TypeSerializer<DT>) registry.getSerializer(type);
         } catch (final IOException e) {
-            if (pdtRegistry != null && 
pdtRegistry.getAdapterByClass(type).isPresent()) {
-                return (TypeSerializer<DT>) 
registry.getSerializer(DataType.COMPOSITE_PDT);
+            if (pdtRegistry != null) {
+                if (pdtRegistry.getAdapterByClass(type).isPresent()) {
+                    return (TypeSerializer<DT>) 
registry.getSerializer(DataType.COMPOSITE_PDT);
+                }
+                if (pdtRegistry.getPrimitiveAdapterByClass(type).isPresent()) {
+                    return (TypeSerializer<DT>) 
registry.getSerializer(DataType.PRIMITIVE_PDT);
+                }
             }
             throw e;
         }
@@ -205,4 +217,14 @@ public class GraphBinaryWriter {
         return ProviderDefinedType.from(value);
     }
 
+    /**
+     * Dehydrates a value to a {@link PrimitiveProviderDefinedType} using a 
{@link PrimitivePDTAdapter} from the
+     * pdtRegistry.
+     */
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    private PrimitiveProviderDefinedType dehydrateToPrimitivePdt(final Object 
value, final Class<?> objectClass) {
+        final PrimitivePDTAdapter adapter = (PrimitivePDTAdapter) 
pdtRegistry.getPrimitiveAdapterByClass(objectClass).get();
+        return new PrimitiveProviderDefinedType(adapter.typeName(), 
adapter.toValue(value));
+    }
+
 }
diff --git 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/PrimitivePDTAdapter.java
 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/PrimitivePDTAdapter.java
new file mode 100644
index 0000000000..670feb1118
--- /dev/null
+++ 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/PrimitivePDTAdapter.java
@@ -0,0 +1,28 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.tinkerpop.gremlin.structure.io.pdt;
+
+/**
+ * Adapter for converting between a typed object and a {@link 
PrimitiveProviderDefinedType} string value.
+ * Used for single-value (primitive) provider-defined types.
+ */
+public interface PrimitivePDTAdapter<T> extends ProviderDefinedTypeAdapter<T> {
+    String toValue(T obj);
+    T fromValue(String value);
+}
diff --git 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistry.java
 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistry.java
index 4213f4ec94..bb3b7eb3f4 100644
--- 
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistry.java
+++ 
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistry.java
@@ -42,6 +42,8 @@ public final class ProviderDefinedTypeRegistry {
 
     private final Map<String, CompositePDTAdapter<?>> adaptersByName = new 
ConcurrentHashMap<>();
     private final Map<Class<?>, CompositePDTAdapter<?>> adaptersByClass = new 
ConcurrentHashMap<>();
+    private final Map<String, PrimitivePDTAdapter<?>> primitiveAdaptersByName 
= new ConcurrentHashMap<>();
+    private final Map<Class<?>, PrimitivePDTAdapter<?>> 
primitiveAdaptersByClass = new ConcurrentHashMap<>();
 
     private ProviderDefinedTypeRegistry() {}
 
@@ -65,12 +67,24 @@ public final class ProviderDefinedTypeRegistry {
     }
 
     /**
-     * Registers an adapter. Composite adapters ({@link CompositePDTAdapter}) 
are stored for
-     * hydration/dehydration; other adapter kinds are routed to their 
respective maps in future beads.
+     * Registers an adapter. Composite adapters ({@link CompositePDTAdapter}) 
are stored in composite maps;
+     * primitive adapters ({@link PrimitivePDTAdapter}) are stored in 
primitive maps.
+     *
+     * @throws IllegalArgumentException if the adapter's target class is 
already registered under the other kind
      */
     public void register(final ProviderDefinedTypeAdapter<?> adapter) {
-        if (adapter instanceof CompositePDTAdapter) {
+        if (adapter instanceof PrimitivePDTAdapter) {
+            final PrimitivePDTAdapter<?> primitive = (PrimitivePDTAdapter<?>) 
adapter;
+            if (adaptersByClass.containsKey(primitive.targetClass()))
+                throw new IllegalArgumentException("Class " + 
primitive.targetClass().getName() +
+                        " is already registered as a composite PDT adapter");
+            primitiveAdaptersByName.put(primitive.typeName(), primitive);
+            primitiveAdaptersByClass.put(primitive.targetClass(), primitive);
+        } else if (adapter instanceof CompositePDTAdapter) {
             final CompositePDTAdapter<?> composite = (CompositePDTAdapter<?>) 
adapter;
+            if (primitiveAdaptersByClass.containsKey(composite.targetClass()))
+                throw new IllegalArgumentException("Class " + 
composite.targetClass().getName() +
+                        " is already registered as a primitive PDT adapter");
             adaptersByName.put(composite.typeName(), composite);
             adaptersByClass.put(composite.targetClass(), composite);
         }
@@ -96,6 +110,14 @@ public final class ProviderDefinedTypeRegistry {
         return Optional.ofNullable(adaptersByClass.get(clazz));
     }
 
+    public Optional<PrimitivePDTAdapter<?>> getPrimitiveAdapterByName(final 
String name) {
+        return Optional.ofNullable(primitiveAdaptersByName.get(name));
+    }
+
+    public Optional<PrimitivePDTAdapter<?>> getPrimitiveAdapterByClass(final 
Class<?> clazz) {
+        return Optional.ofNullable(primitiveAdaptersByClass.get(clazz));
+    }
+
     /**
      * Attempts to hydrate a {@link ProviderDefinedType} into a typed object 
using a registered adapter.
      * Recursively hydrates nested PDT values in the fields map (including 
those inside Lists, Sets,
@@ -136,6 +158,8 @@ public final class ProviderDefinedTypeRegistry {
     private Object hydrateValue(final Object value) {
         if (value instanceof ProviderDefinedType)
             return hydrate((ProviderDefinedType) value);
+        if (value instanceof PrimitiveProviderDefinedType)
+            return hydratePrimitive((PrimitiveProviderDefinedType) value);
         if (value instanceof List) {
             final List<Object> result = new ArrayList<>();
             for (final Object item : (List<?>) value)
@@ -157,6 +181,28 @@ public final class ProviderDefinedTypeRegistry {
         return value;
     }
 
+    /**
+     * Attempts to hydrate a {@link PrimitiveProviderDefinedType} into a typed 
object using a registered
+     * {@link PrimitivePDTAdapter}. Returns the original primitive PDT if no 
adapter is found or if the
+     * adapter throws an exception.
+     */
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    public Object hydratePrimitive(final PrimitiveProviderDefinedType pdt) {
+        final PrimitivePDTAdapter adapter = 
primitiveAdaptersByName.get(pdt.getName());
+        if (adapter == null) {
+            logger.warn("No PrimitivePDTAdapter registered for '{}', returning 
raw PrimitiveProviderDefinedType",
+                    pdt.getName());
+            return pdt;
+        }
+        try {
+            return adapter.fromValue(pdt.getValue());
+        } catch (final Exception e) {
+            logger.warn("Failed to hydrate PrimitiveProviderDefinedType '{}', 
returning raw: {}",
+                    pdt.getName(), e.getMessage());
+            return pdt;
+        }
+    }
+
     /**
      * A reflective adapter synthesized from a {@link 
ProviderDefined}-annotated class.
      */
diff --git 
a/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistryTest.java
 
b/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistryTest.java
index 7158cb71f5..3442038337 100644
--- 
a/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistryTest.java
+++ 
b/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/structure/io/pdt/ProviderDefinedTypeRegistryTest.java
@@ -413,4 +413,145 @@ public class ProviderDefinedTypeRegistryTest {
         assertEquals(10, ((Point) innerValue).x);
         assertEquals(20, ((Point) innerValue).y);
     }
+
+    // === Primitive PDT Adapter tests ===
+
+    static class Uint32 {
+        final long value;
+        Uint32(long value) { this.value = value; }
+    }
+
+    static class Uint32Adapter implements PrimitivePDTAdapter<Uint32> {
+        @Override public String typeName() { return "Uint32"; }
+        @Override public Class<Uint32> targetClass() { return Uint32.class; }
+        @Override public String toValue(Uint32 obj) { return 
Long.toString(obj.value); }
+        @Override public Uint32 fromValue(String value) { return new 
Uint32(Long.parseLong(value)); }
+    }
+
+    static class FailingPrimitiveAdapter implements 
PrimitivePDTAdapter<Uint32> {
+        @Override public String typeName() { return "FailPrim"; }
+        @Override public Class<Uint32> targetClass() { return Uint32.class; }
+        @Override public String toValue(Uint32 obj) { return "0"; }
+        @Override public Uint32 fromValue(String value) { throw new 
RuntimeException("intentional primitive failure"); }
+    }
+
+    @Test
+    public void shouldRegisterAndLookUpPrimitiveAdapterByName() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new Uint32Adapter());
+
+        final Optional<PrimitivePDTAdapter<?>> found = 
registry.getPrimitiveAdapterByName("Uint32");
+        assertTrue(found.isPresent());
+        assertEquals("Uint32", found.get().typeName());
+    }
+
+    @Test
+    public void shouldRegisterAndLookUpPrimitiveAdapterByClass() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new Uint32Adapter());
+
+        final Optional<PrimitivePDTAdapter<?>> found = 
registry.getPrimitiveAdapterByClass(Uint32.class);
+        assertTrue(found.isPresent());
+        assertEquals(Uint32.class, found.get().targetClass());
+    }
+
+    @Test
+    public void shouldHydratePrimitive() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new Uint32Adapter());
+
+        final PrimitiveProviderDefinedType pdt = new 
PrimitiveProviderDefinedType("Uint32", "42");
+        final Object result = registry.hydratePrimitive(pdt);
+        assertTrue(result instanceof Uint32);
+        assertEquals(42L, ((Uint32) result).value);
+    }
+
+    @Test
+    public void shouldReturnRawPrimitivePdtWhenNoAdapterRegistered() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+
+        final PrimitiveProviderDefinedType pdt = new 
PrimitiveProviderDefinedType("Unknown", "x");
+        final Object result = registry.hydratePrimitive(pdt);
+        assertSame(pdt, result);
+    }
+
+    @Test
+    public void shouldReturnRawPrimitivePdtWhenAdapterThrows() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new FailingPrimitiveAdapter());
+
+        final PrimitiveProviderDefinedType pdt = new 
PrimitiveProviderDefinedType("FailPrim", "42");
+        final Object result = registry.hydratePrimitive(pdt);
+        assertSame(pdt, result);
+    }
+
+    @Test
+    public void shouldThrowOnDualRegistrationPrimitiveAfterComposite() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new PointAdapter());
+
+        // Attempt to register Point.class as a primitive (already registered 
as composite)
+        final PrimitivePDTAdapter<Point> primitivePoint = new 
PrimitivePDTAdapter<Point>() {
+            @Override public String typeName() { return "PointPrim"; }
+            @Override public Class<Point> targetClass() { return Point.class; }
+            @Override public String toValue(Point obj) { return obj.x + "," + 
obj.y; }
+            @Override public Point fromValue(String value) { return new 
Point(0, 0); }
+        };
+
+        try {
+            registry.register(primitivePoint);
+            fail("Expected IllegalArgumentException for dual registration");
+        } catch (final IllegalArgumentException e) {
+            assertTrue(e.getMessage().contains("already registered as a 
composite"));
+        }
+    }
+
+    @Test
+    public void shouldThrowOnDualRegistrationCompositeAfterPrimitive() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new Uint32Adapter());
+
+        // Attempt to register Uint32.class as a composite (already registered 
as primitive)
+        final CompositePDTAdapter<Uint32> compositeUint32 = new 
CompositePDTAdapter<Uint32>() {
+            @Override public String typeName() { return "Uint32Comp"; }
+            @Override public Class<Uint32> targetClass() { return 
Uint32.class; }
+            @Override public Map<String, Object> toFields(Uint32 obj) { return 
new HashMap<>(); }
+            @Override public Uint32 fromFields(Map<String, Object> fields) { 
return new Uint32(0); }
+        };
+
+        try {
+            registry.register(compositeUint32);
+            fail("Expected IllegalArgumentException for dual registration");
+        } catch (final IllegalArgumentException e) {
+            assertTrue(e.getMessage().contains("already registered as a 
primitive"));
+        }
+    }
+
+    @Test
+    public void shouldHydratePrimitiveNestedInsideComposite() {
+        final ProviderDefinedTypeRegistry registry = 
ProviderDefinedTypeRegistry.empty();
+        registry.register(new Uint32Adapter());
+
+        // A composite type "Container" with a primitive nested field
+        registry.register(new CompositePDTAdapter<Map>() {
+            @Override public String typeName() { return "Container"; }
+            @Override public Class<Map> targetClass() { return Map.class; }
+            @Override public Map<String, Object> toFields(Map obj) { return 
new HashMap<>(); }
+            @SuppressWarnings("unchecked")
+            @Override public Map fromFields(Map<String, Object> fields) { 
return fields; }
+        });
+
+        final Map<String, Object> containerFields = new HashMap<>();
+        containerFields.put("id", new PrimitiveProviderDefinedType("Uint32", 
"99"));
+        containerFields.put("label", "test");
+        final ProviderDefinedType containerPdt = new 
ProviderDefinedType("Container", containerFields);
+
+        final Object result = registry.hydrate(containerPdt);
+        assertTrue(result instanceof Map);
+        @SuppressWarnings("unchecked")
+        final Map<String, Object> resultMap = (Map<String, Object>) result;
+        assertTrue(resultMap.get("id") instanceof Uint32);
+        assertEquals(99L, ((Uint32) resultMap.get("id")).value);
+        assertEquals("test", resultMap.get("label"));
+    }
 }
diff --git 
a/gremlin-util/src/test/java/org/apache/tinkerpop/gremlin/util/ser/binary/GraphBinaryWriterPdtTest.java
 
b/gremlin-util/src/test/java/org/apache/tinkerpop/gremlin/util/ser/binary/GraphBinaryWriterPdtTest.java
index 919d9ba118..0d57c515e5 100644
--- 
a/gremlin-util/src/test/java/org/apache/tinkerpop/gremlin/util/ser/binary/GraphBinaryWriterPdtTest.java
+++ 
b/gremlin-util/src/test/java/org/apache/tinkerpop/gremlin/util/ser/binary/GraphBinaryWriterPdtTest.java
@@ -24,6 +24,8 @@ import 
org.apache.tinkerpop.gremlin.structure.io.binary.GraphBinaryReader;
 import org.apache.tinkerpop.gremlin.structure.io.binary.GraphBinaryWriter;
 import org.apache.tinkerpop.gremlin.structure.io.binary.TypeSerializerRegistry;
 import org.apache.tinkerpop.gremlin.structure.io.pdt.CompositePDTAdapter;
+import org.apache.tinkerpop.gremlin.structure.io.pdt.PrimitivePDTAdapter;
+import 
org.apache.tinkerpop.gremlin.structure.io.pdt.PrimitiveProviderDefinedType;
 import org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefined;
 import org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedType;
 import 
org.apache.tinkerpop.gremlin.structure.io.pdt.ProviderDefinedTypeRegistry;
@@ -133,4 +135,77 @@ public class GraphBinaryWriterPdtTest {
         final ProviderDefinedType result = reader.read(buffer);
         assertEquals(pdt, result);
     }
+
+    // === Primitive PDT Adapter write-path tests ===
+
+    static class Uint32 {
+        final long value;
+        Uint32(long value) { this.value = value; }
+    }
+
+    static class Uint32Adapter implements PrimitivePDTAdapter<Uint32> {
+        @Override public String typeName() { return "Uint32"; }
+        @Override public Class<Uint32> targetClass() { return Uint32.class; }
+        @Override public String toValue(Uint32 obj) { return 
Long.toString(obj.value); }
+        @Override public Uint32 fromValue(String value) { return new 
Uint32(Long.parseLong(value)); }
+    }
+
+    @Test
+    public void shouldDehydratePrimitiveAdapterOnWritePathAndHydrateBack() 
throws IOException {
+        final ProviderDefinedTypeRegistry pdtRegistry = 
ProviderDefinedTypeRegistry.empty();
+        pdtRegistry.register(new Uint32Adapter());
+
+        final GraphBinaryWriter registryWriter = new 
GraphBinaryWriter(TypeSerializerRegistry.INSTANCE, pdtRegistry);
+        final GraphBinaryReader registryReader = new 
GraphBinaryReader(TypeSerializerRegistry.INSTANCE, pdtRegistry);
+
+        final Uint32 original = new Uint32(12345L);
+
+        final Buffer buffer = bufferFactory.create(allocator.buffer());
+        registryWriter.write(original, buffer);
+        buffer.readerIndex(0);
+
+        final Uint32 result = registryReader.read(buffer);
+        assertEquals(12345L, result.value);
+    }
+
+    @Test
+    public void shouldRoundTripPrimitiveProviderDefinedTypeWithoutRegistry() 
throws IOException {
+        final PrimitiveProviderDefinedType pdt = new 
PrimitiveProviderDefinedType("Uint32", "99");
+
+        final Buffer buffer = bufferFactory.create(allocator.buffer());
+        writer.write(pdt, buffer);
+        buffer.readerIndex(0);
+
+        final PrimitiveProviderDefinedType result = reader.read(buffer);
+        assertEquals(pdt, result);
+    }
+
+    @Test
+    public void shouldRoundTripPrimitiveNestedInComposite() throws IOException 
{
+        final ProviderDefinedTypeRegistry pdtRegistry = 
ProviderDefinedTypeRegistry.empty();
+        pdtRegistry.register(new Uint32Adapter());
+        pdtRegistry.register(new UnannotatedTypeAdapter());
+
+        final GraphBinaryWriter registryWriter = new 
GraphBinaryWriter(TypeSerializerRegistry.INSTANCE, pdtRegistry);
+        final GraphBinaryReader registryReader = new 
GraphBinaryReader(TypeSerializerRegistry.INSTANCE, pdtRegistry);
+
+        // Build a composite PDT with a nested primitive value
+        final Map<String, Object> fields = new LinkedHashMap<>();
+        fields.put("value", 7);
+        fields.put("id", new PrimitiveProviderDefinedType("Uint32", "42"));
+        final ProviderDefinedType compositePdt = new 
ProviderDefinedType("UnannotatedType", fields);
+
+        final Buffer buffer = bufferFactory.create(allocator.buffer());
+        registryWriter.write(compositePdt, buffer);
+        buffer.readerIndex(0);
+
+        // The reader hydrates the composite (via UnannotatedTypeAdapter) and 
the nested primitive
+        // should have been hydrated to Uint32 by the registry's hydrateValue 
recursion
+        final Object result = registryReader.read(buffer);
+        assertTrue(result instanceof UnannotatedType);
+        // Note: UnannotatedTypeAdapter only maps "value" field to an int, so 
the hydrated "id" field
+        // ends up being handled during the composite adapter's fromFields. 
Since the adapter
+        // only reads "value", we verify the composite round-tripped correctly.
+        assertEquals(7, ((UnannotatedType) result).value);
+    }
 }

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