test: add SqlParameter datetime test with custom serializer

Adds queryWithSqlParameterDateTimeAndCustomSerializer test that validates
the end-to-end scenario: when a custom serializer writes Instant as an
ISO-8601 string (not a timestamp), SqlParameter must apply the same
serializer so the query filter matches the stored representation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: xinlian12

sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/CosmosItemSerializerTest.java

@@ -45,6 +45,7 @@
 import org.testng.annotations.Factory;
 import org.testng.annotations.Test;
 
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
@@ -923,6 +924,62 @@ public void queryWithSqlParameterAndCustomSerializer() {
         }
     }
 
+    @Test(groups = { "fast", "emulator" }, timeOut = TIMEOUT * 1000000)
+    public void queryWithSqlParameterDateTimeAndCustomSerializer() {
+        CosmosItemSerializer clientSerializer = this.getClientBuilder().getCustomItemSerializer();
+        if (clientSerializer == null || clientSerializer == CosmosItemSerializer.DEFAULT_SERIALIZER) {
+            return;
+        }
+
+        boolean isEnvelopeWrapper = clientSerializer instanceof EnvelopWrappingItemSerializer;
+        if (isEnvelopeWrapper) {
+            return;
+        }
+
+        // This test validates that when a custom serializer changes how values are
+        // stored (e.g. Instant as ISO-8601 string instead of a timestamp number),
+        // SqlParameter correctly applies the same serializer so that query filters
+        // match the stored representation.
+        String id = UUID.randomUUID().toString();
+        String pkValue = id;
+        Instant createdAt = Instant.parse("2026-03-15T10:30:00Z");
+        TestDocumentWithTimestamp doc = new TestDocumentWithTimestamp();
+        doc.id = id;
+        doc.mypk = pkValue;
+        doc.createdAt = createdAt;
+        doc.description = "test-datetime-serialization";
+
+        try {
+            CosmosItemRequestOptions requestOptions = new CosmosItemRequestOptions()
+                .setCustomItemSerializer(clientSerializer);
+            container.createItem(doc, new PartitionKey(pkValue), requestOptions);
+
+            CosmosQueryRequestOptions queryRequestOptions = new CosmosQueryRequestOptions()
+                .setCustomItemSerializer(clientSerializer);
+
+            // Query using SqlParameter with the same Instant value — the custom serializer
+            // must serialize the parameter the same way as the document field.
+            SqlQuerySpec querySpec = new SqlQuerySpec(
+                "SELECT * FROM c WHERE c.createdAt = @createdAt AND c.id = @id",
+                new SqlParameter("@createdAt", createdAt),
+                new SqlParameter("@id", id));
+
+            List<TestDocumentWithTimestamp> results = container
+                .queryItems(querySpec, queryRequestOptions, TestDocumentWithTimestamp.class)
+                .stream().collect(Collectors.toList());
+
+            assertThat(results).isNotNull();
+            assertThat(results).hasSize(1);
+            assertThat(results.get(0).id).isEqualTo(id);
+            assertThat(results.get(0).createdAt).isEqualTo(createdAt);
+            assertThat(results.get(0).description).isEqualTo("test-datetime-serialization");
+        } finally {
+            try {
+                container.deleteItem(id, new PartitionKey(pkValue), new CosmosItemRequestOptions());
+            } catch (Exception ignored) { }
+        }
+    }
+
     private <T> void runBatchAndChangeFeedTestCase(
         Function<String, T> docGenerator,
         CosmosItemSerializer requestLevelSerializer,
@@ -1153,6 +1210,13 @@ private static class TestDocumentWithNullableField {
         public String nullableField;
     }
 
+    private static class TestDocumentWithTimestamp {
+        public String id;
+        public String mypk;
+        public Instant createdAt;
+        public String description;
+    }
+
     private static class TestDocumentWrappedInEnvelope {
         public String id;