fix: use UTC for Arrow schema timezone in SparkToColumnar conversions

common/src/main/scala/org/apache/comet/CometConf.scala

@@ -222,31 +222,28 @@ object CometConf extends ShimCometConf {
 
   val COMET_CONVERT_FROM_PARQUET_ENABLED: ConfigEntry[Boolean] =
     conf("spark.comet.convert.parquet.enabled")
-      .category(CATEGORY_TESTING)
+      .category(CATEGORY_EXEC)
       .doc(
         "When enabled, data from Spark (non-native) Parquet v1 and v2 scans will be converted to " +
-          "Arrow format.  This is an experimental feature and has known issues with " +
-          "non-UTC timezones.")
+          "Arrow format.")
       .booleanConf
       .createWithDefault(false)
 
   val COMET_CONVERT_FROM_JSON_ENABLED: ConfigEntry[Boolean] =
     conf("spark.comet.convert.json.enabled")
-      .category(CATEGORY_TESTING)
+      .category(CATEGORY_EXEC)
       .doc(
         "When enabled, data from Spark (non-native) JSON v1 and v2 scans will be converted to " +
-          "Arrow format. This is an experimental feature and has known issues with " +
-          "non-UTC timezones.")
+          "Arrow format.")
       .booleanConf
       .createWithDefault(false)
 
   val COMET_CONVERT_FROM_CSV_ENABLED: ConfigEntry[Boolean] =
     conf("spark.comet.convert.csv.enabled")
-      .category(CATEGORY_TESTING)
+      .category(CATEGORY_EXEC)
       .doc(
         "When enabled, data from Spark (non-native) CSV v1 and v2 scans will be converted to " +
-          "Arrow format. This is an experimental feature and has known issues with " +
-          "non-UTC timezones.")
+          "Arrow format.")
       .booleanConf
       .createWithDefault(false)
 
@@ -743,17 +740,17 @@ object CometConf extends ShimCometConf {
 
   val COMET_SPARK_TO_ARROW_ENABLED: ConfigEntry[Boolean] =
     conf("spark.comet.sparkToColumnar.enabled")
-      .category(CATEGORY_TESTING)
+      .category(CATEGORY_EXEC)
       .doc("Whether to enable Spark to Arrow columnar conversion. When this is turned on, " +
         "Comet will convert operators in " +
         "`spark.comet.sparkToColumnar.supportedOperatorList` into Arrow columnar format before " +
-        "processing. This is an experimental feature and has known issues with non-UTC timezones.")
+        "processing.")
       .booleanConf
       .createWithDefault(false)
 
   val COMET_SPARK_TO_ARROW_SUPPORTED_OPERATOR_LIST: ConfigEntry[Seq[String]] =
     conf("spark.comet.sparkToColumnar.supportedOperatorList")
-      .category(CATEGORY_TESTING)
+      .category(CATEGORY_EXEC)
       .doc("A comma-separated list of operators that will be converted to Arrow columnar " +
         s"format when `${COMET_SPARK_TO_ARROW_ENABLED.key}` is true.")
       .stringConf

spark/src/main/scala/org/apache/spark/sql/comet/CometLocalTableScanExec.scala

@@ -66,7 +66,8 @@ case class CometLocalTableScanExec(
   override def doExecuteColumnar(): RDD[ColumnarBatch] = {
     val numInputRows = longMetric("numOutputRows")
     val maxRecordsPerBatch = CometConf.COMET_BATCH_SIZE.get(conf)
-    val timeZoneId = conf.sessionLocalTimeZone
+    // Use UTC to match native side expectations. See CometSparkToColumnarExec.
+    val timeZoneId = "UTC"
     rdd.mapPartitionsInternal { sparkBatches =>
       val context = TaskContext.get()
       val batches = CometArrowConverters.rowToArrowBatchIter(

spark/src/main/scala/org/apache/spark/sql/comet/CometSparkToColumnarExec.scala

@@ -97,7 +97,12 @@ case class CometSparkToColumnarExec(child: SparkPlan)
     val numOutputBatches = longMetric("numOutputBatches")
     val conversionTime = longMetric("conversionTime")
     val maxRecordsPerBatch = CometConf.COMET_BATCH_SIZE.get(conf)
-    val timeZoneId = conf.sessionLocalTimeZone
+    // Use UTC for Arrow schema timezone to match the native side, which always
+    // deserializes Timestamp as Timestamp(Microsecond, Some("UTC")). Spark's internal
+    // timestamp representation is always UTC microseconds, so the timezone here is
+    // purely schema metadata. Using session timezone would cause Arrow RowConverter
+    // schema mismatch errors in non-UTC sessions. See COMET-2720.
+    val timeZoneId = "UTC"
     val schema = child.schema
 
     if (child.supportsColumnar) {

spark/src/test/scala/org/apache/comet/exec/CometExecSuite.scala

@@ -2173,6 +2173,42 @@ class CometExecSuite extends CometTestBase {
     }
   }
 
+  test("LocalTableScanExec with timestamps in non-UTC timezone") {
+    withSQLConf(
+      CometConf.COMET_EXEC_LOCAL_TABLE_SCAN_ENABLED.key -> "true",
+      SESSION_LOCAL_TIMEZONE.key -> "America/Los_Angeles") {
+      val df = Seq(
+        (1, java.sql.Timestamp.valueOf("2024-01-15 10:30:00")),
+        (2, java.sql.Timestamp.valueOf("2024-06-15 14:00:00")),
+        (3, java.sql.Timestamp.valueOf("2024-12-25 08:00:00")))
+        .toDF("id", "ts")
+        .orderBy("ts")
+      checkSparkAnswerAndOperator(df)
+    }
+  }
+
+  test("sort on timestamps with non-UTC timezone via LocalTableScan") {
+    // When session timezone is non-UTC, CometLocalTableScanExec and
+    // CometSparkToColumnarExec must use UTC for the Arrow schema timezone
+    // to match the native side's expectations. Without this, the native
+    // ScanExec sees a timezone mismatch and performs an unnecessary cast.
+    // The cast is currently a no-op (Arrow timestamps with timezone are
+    // always UTC microseconds), but using UTC avoids the overhead and
+    // keeps schemas consistent throughout the native plan.
+    withSQLConf(
+      CometConf.COMET_EXEC_LOCAL_TABLE_SCAN_ENABLED.key -> "true",
+      SESSION_LOCAL_TIMEZONE.key -> "America/Los_Angeles") {
+      val df = Seq(
+        (1, java.sql.Timestamp.valueOf("2024-01-15 10:30:00")),
+        (2, java.sql.Timestamp.valueOf("2024-06-15 14:00:00")),
+        (3, java.sql.Timestamp.valueOf("2024-12-25 08:00:00")))
+        .toDF("id", "ts")
+        .repartition(2)
+        .orderBy("ts")
+      checkSparkAnswer(df)
+    }
+  }
+
 }
 
 case class BucketedTableTestSpec(