fix(spark): warn that overwrite destructively deletes existing files

The overwrite branch in `VortexBatchWrite.createBatchWriterFactory` already
deletes the existing files before writing new data, but it logged
`overwrite currently does not do anything for vortex format`, which directly
contradicts the delete on the line above and hides a genuinely dangerous
operation: the delete is a pre-delete, and `abort()` only removes the newly
written files, so it cannot restore what was deleted if the write later fails.

Replace the misleading message with a WARN that states how many files under
which path are being deleted and that the operation cannot be undone if the
subsequent write fails. This also folds in the file count previously logged at
INFO, so it is a single, accurate log line. No write/delete behavior changes.

Signed-off-by: jackylee <qcsd2011@gmail.com>

Author: jackylee-ch

java/vortex-spark/src/main/java/dev/vortex/spark/write/VortexBatchWrite.java

@@ -90,9 +90,15 @@ public DataWriterFactory createBatchWriterFactory(PhysicalWriteInfo info) {
         if (overwrite) {
             var session = VortexSparkSession.get(options);
             var uris = NativeFiles.listFiles(session, outputPath, options);
-            log.info("truncating table with {} files", uris.size());
+            // Deleting the existing files is destructive and happens before the new data is written:
+            // if the subsequent write fails, abort() only removes the newly written files and cannot
+            // restore what was deleted here. Log loudly so operators can see what was removed.
+            log.warn(
+                    "Deleting {} existing file(s) under {} because of overwrite, before writing new data; "
+                            + "this cannot be undone if the subsequent write fails",
+                    uris.size(),
+                    outputPath);
             NativeFiles.delete(session, uris.toArray(new String[0]), options);
-            log.warn("overwrite currently does not do anything for vortex format");
         }
 
         return new VortexDataWriterFactory(outputPath, schema, options, resolvedTransforms);