Fix Windows path split in orphan-tail drainer test

testPreAdoptionSetupFailureDoesNotQuarantineTheSlot derived the slot's
parent directory with slotPath.substring(0, slotPath.lastIndexOf('/')).
File.getAbsolutePath() yields '\' separators on Windows, so lastIndexOf
returned -1 and substring threw StringIndexOutOfBoundsException before
the test reached a single assertion. It was the only failure in the
Windows CI run (2684 tests, 1 error).

Paths.get(slotPath).getParent() derives the parent portably. The join
stays a forward slash on purpose: SlotLock.resolveLogicalLock builds the
lock directory as parentPath + "/" + ".slot-locks", and the blocking
file this test plants must land on the exact string acquireLogical will
mkdir. Deriving the whole path through Paths.get would yield
'\.slot-locks' on Windows, putting the file where acquireLogical never
looks, so the test would pass while exercising nothing. SlotLockTest
already documents that trap for its sibling.

Verified both ways on macOS: the test passes with this change, and still
fails with "a slot this drainer never adopted must not be quarantined"
when the BackgroundDrainer engine != null guard it pins is reverted.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: glasstiger

core/src/test/java/io/questdb/client/test/cutlass/qwp/client/sf/cursor/BackgroundDrainerOrphanTailTest.java

@@ -35,6 +35,7 @@
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 
+import java.nio.file.Paths;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.junit.Assert.assertEquals;
@@ -108,7 +109,12 @@ public void testPreAdoptionSetupFailureDoesNotQuarantineTheSlot() throws Excepti
             try (CursorSendEngine engine = new CursorSendEngine(slotPath, SEGMENT_SIZE_BYTES)) {
                 appendDeferredFrame(engine);
             }
-            String parent = slotPath.substring(0, slotPath.lastIndexOf('/'));
+            // Derive the parent with Paths.get (portable: getAbsolutePath yields '\'
+            // separators on Windows, so lastIndexOf('/') returns -1 and substring
+            // throws), then join with a FORWARD slash -- SlotLock.resolveLogicalLock
+            // builds `parentPath + "/" + ".slot-locks"` exactly that way, and the
+            // blocking file must land on the same string acquireLogical will mkdir.
+            String parent = Paths.get(slotPath).getParent().toString();
             String lockDirPath = parent + "/.slot-locks";
             int fd = Files.openRW(lockDirPath);
             assertTrue("could not plant the blocking file", fd > -1);