fix(language-web): try to avoid leaking websockets

subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java

@@ -146,7 +146,6 @@ public void onSubscribeToPrecomputationEvents(String resourceId, PushWebDocument
 	/**
 	 * Get the injector to satisfy the request in the {@code serviceContext}.
 	 *
-	 *
 	 * @param context the Xtext service context of the request
 	 * @return the injector for the Xtext language in the request
 	 * @throws UnknownLanguageException if the Xtext language cannot be determined

subprojects/language-web/src/main/java/tools/refinery/language/web/xtext/servlet/XtextWebSocket.java

@@ -79,6 +79,9 @@ public void onClose(int statusCode, String reason) {
 			LOG.warn("{} closed connection with status code {}: {}", webSocketSession.getRemoteSocketAddress(),
 					statusCode, reason);
 		}
+		if (!webSocketSession.isOpen()) {
+			webSocketSession.close();
+		}
 		webSocketSession = null;
 	}
 
@@ -91,10 +94,10 @@ public void onError(Throwable error) {
 		switch (error) {
 		case WebSocketTimeoutException ignored -> LOG.warn("Websocket connection timed out", error);
 		case EofException ignored -> LOG.warn("Websocket connection already closed", error);
-		default ->
-				LOG.error("Internal websocket error in connection from " + webSocketSession.getRemoteSocketAddress(),
-						error);
+		default -> LOG.error("Internal websocket error in connection from " + webSocketSession.getRemoteSocketAddress(),
+				error);
 		}
+		webSocketSession.close();
 	}
 
 	@OnWebSocketMessage
@@ -148,5 +151,6 @@ public void writeFailed(Throwable x) {
 			return;
 		}
 		LOG.warn("Cannot complete async write to websocket " + webSocketSession.getRemoteSocketAddress(), x);
+		webSocketSession.close();
 	}
 }