ipc transport: use Jupyter's {ip}-{port} socket address format #134

jjava-jupyter/src/main/java/org/dflib/jjava/jupyter/channels/JupyterSocket.java

@@ -39,8 +39,14 @@
 
 public abstract class JupyterSocket extends ZMQ.Socket {
 
+    /**
+     * Builds a ZeroMQ endpoint for a channel from the connection file properties. For the {@code ipc} transport,
+     * Jupyter treats {@code ip} as a base path and names each channel socket {@code "{ip}-{port}"}
+     * (this is what {@code jupyter_client} writes and what frontends connect to).
+     */
     protected static String formatAddress(String transport, String ip, int port) {
-        return transport + "://" + ip + ":" + port;
+        String separator = "ipc".equalsIgnoreCase(transport) ? "-" : ":";
+        return transport + "://" + ip + separator + port;
     }
 
     // Comes from a Python bytestring

jjava-jupyter/src/test/java/org/dflib/jjava/jupyter/channels/JupyterSocketTest.java

@@ -0,0 +1,19 @@
+package org.dflib.jjava.jupyter.channels;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class JupyterSocketTest {
+
+    @Test
+    public void formatAddress_tcp() {
+        assertEquals("tcp://127.0.0.1:54321", JupyterSocket.formatAddress("tcp", "127.0.0.1", 54321));
+    }
+
+    @Test
+    public void formatAddress_ipc() {
+        // Jupyter convention: "ip" is a base path, channel sockets are "{ip}-{port}"
+        assertEquals("ipc:///tmp/kernel-abc-1", JupyterSocket.formatAddress("ipc", "/tmp/kernel-abc", 1));
+    }
+}