fix: close pipe readers before join() to prevent conformance test hang (#259)

assertMatchesParquetOracle streams the vortex-java CSV export and the
parquet oracle through a PipedWriter/PipedReader pair on two virtual
threads, compared line-by-line by the main thread. If assertFilesMatch
stops reading early (oracle abort, line mismatch), nobody drains the
pipe anymore — a producer still writing blocks forever once its 128KB
buffer fills, and the unconditional join() right after hangs forever.

Never surfaced before #257 because every prior repeated/list column
consumer failed fast (VortexException thrown immediately). #257 is
the first case where the Java side succeeds and outruns an
early-exiting reader (confirmed via jstack: main thread parked on
Thread.join() for 18+ minutes, ~4s CPU time).

Close both readers before join() so a producer parked on a full
buffer gets an IOException instead of blocking; the artificial
"Pipe closed" error ranks below the real captured errors in the
existing priority order, so behavior is unchanged on every other path.

Author: dfa1

integration/src/test/java/io/github/dfa1/vortex/integration/RaincloudConformanceIntegrationTest.java

@@ -18,6 +18,7 @@
 import org.opentest4j.TestAbortedException;
 
 import java.io.BufferedReader;
+import java.io.Closeable;
 import java.io.IOException;
 import java.io.PipedReader;
 import java.io.PipedWriter;
@@ -122,6 +123,14 @@ private static void assertMatchesParquetOracle(Path vortex, Path parquet) throws
                 assertFilesMatch(vortexReader, oracleReader);
             } catch (Throwable t) {
                 mainError = t;
+            } finally {
+                // assertFilesMatch may stop reading early (oracle abort, line mismatch) while a
+                // producer is still writing — closing the read end here, rather than relying on
+                // the outer try-with-resources (which only runs after join() below), unblocks a
+                // producer parked on a full PipedWriter buffer with a "Pipe closed" IOException
+                // instead of hanging join() forever (#259).
+                closeQuietly(vortexReader);
+                closeQuietly(oracleReader);
             }
 
             try {
@@ -173,6 +182,18 @@ private static void assertMatchesParquetOracle(Path vortex, Path parquet) throws
         }
     }
 
+    /// Closes a stream ignoring the outcome, used only to unblock a producer thread
+    /// parked writing to the other end of a pipe before joining it.
+    ///
+    /// @param closeable the stream to close
+    private static void closeQuietly(Closeable closeable) {
+        try {
+            closeable.close();
+        } catch (IOException ignored) {
+            // best effort: only used to unblock a producer thread before join()
+        }
+    }
+
     /// Runs the full conformance check but reports the outcome as an aborted test
     /// either way: only triaged matrix entries may count as green or red. The abort
     /// message says which way to flip the entry.