Add parameterized test for S3 store access error handling

Tests that both backends report a user-facing error via the error handler
when S3 store access fails. The ZARR_JAVA variant mocks ZarrJavaPyramidBackend
to throw StoreException; the N5 variant relies on N5Exception.N5IOException
being thrown immediately (local failure, no network needed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: stefanhahmann

src/test/java/sc/fiji/ome/zarr/open/ZarrOpenActionsTest.java

@@ -52,6 +52,10 @@
 import org.mockito.MockedConstruction;
 import org.mockito.MockedStatic;
 import org.mockito.Mockito;
+
+import dev.zarr.zarrjava.store.StoreException;
+
+import sc.fiji.ome.zarr.pyramid.backend.zarrjava.ZarrJavaPyramidBackend;
 import org.scijava.Context;
 import org.scijava.display.Display;
 import org.scijava.display.DisplayService;
@@ -678,6 +682,43 @@ void openImageFromS3( final ZarrReaderBackend backend )
 		}
 	}
 
+	@ParameterizedTest
+	@MethodSource( "readerBackends" )
+	@SuppressWarnings( "rawtypes" )
+	void storeAccessErrorIsReportedToErrorHandler( final ZarrReaderBackend backend )
+	{
+		try ( Context context = new Context() )
+		{
+			final URI uri = URI.create( "s3://nonexistent-bucket/some/path" );
+			final AtomicReference< String > capturedError = new AtomicReference<>();
+			final ZarrOpeningSettings settings = new ZarrOpeningSettings();
+			settings.setReaderBackend( backend );
+
+			if ( backend == ZarrReaderBackend.ZARR_JAVA )
+			{
+				try ( MockedConstruction< ZarrJavaPyramidBackend > mock = Mockito.mockConstruction(
+						ZarrJavaPyramidBackend.class,
+						( mockBackend, ctx ) -> Mockito.when( mockBackend.load() )
+								.thenThrow( new StoreException( "Access Denied (403)" ) ) ) )
+				{
+					final ZarrOpenActions actions = new ZarrOpenActions( uri, context, settings, capturedError::set );
+					assertDoesNotThrow( () -> actions.openImage( dataset -> null, img -> null ) );
+					assertEquals( 1, mock.constructed().size(), "Expected exactly one ZarrJavaPyramidBackend to be constructed" );
+				}
+			}
+			else
+			{
+				// N5 backend throws N5Exception.N5IOException immediately (local failure, no network needed)
+				final ZarrOpenActions actions = new ZarrOpenActions( uri, context, settings, capturedError::set );
+				assertDoesNotThrow( () -> actions.openImage( dataset -> null, img -> null ) );
+			}
+
+			assertNotNull( capturedError.get(), "Error handler should have been called for backend " + backend );
+			assertTrue( capturedError.get().contains( uri.toString() ),
+					"Error message should contain the URI for backend " + backend + ", got: " + capturedError.get() );
+		}
+	}
+
 	@Test
 	void testRunScriptWithNoScriptSpecified() throws URISyntaxException, InterruptedException, InvocationTargetException
 	{