test(cli): add comprehensive tests for multi-target resolution and output

Add unit tests for target normalization and address family filtering, and expand integration tests to verify column rendering and CSV output for multiple targets. Update subscriber config to drop oldest events under backpressure for better CLI stability.

crates/irtt-cli/tests/client_multi_target.rs

@@ -28,6 +28,101 @@ impl FakeServer {
     }
 }
 
+#[test]
+fn list_columns_succeeds_without_target() {
+    let output = Command::new(env!("CARGO_BIN_EXE_irtt-cli"))
+        .arg("--list-columns")
+        .output()
+        .unwrap();
+
+    assert!(
+        output.status.success(),
+        "status={:?}\nstderr={}",
+        output.status.code(),
+        String::from_utf8_lossy(&output.stderr)
+    );
+    let stdout = String::from_utf8(output.stdout).unwrap();
+    assert!(stdout.contains("Available event columns:"), "{stdout}");
+    assert!(stdout.contains("target"), "{stdout}");
+}
+
+#[test]
+fn single_target_default_table_omits_target_and_accepts_pacing() {
+    let server = start_echo_server(test_params(
+        Some(Duration::from_millis(30)),
+        Duration::from_millis(10),
+    ));
+
+    let output = Command::new(env!("CARGO_BIN_EXE_irtt-cli"))
+        .args([
+            "--duration",
+            "30ms",
+            "--interval",
+            "10ms",
+            "--pacing",
+            "burst",
+            "--header",
+            "always",
+            &server.addr.to_string(),
+        ])
+        .output()
+        .unwrap();
+
+    server.join();
+
+    assert!(
+        output.status.success(),
+        "status={:?}\nstderr={}",
+        output.status.code(),
+        String::from_utf8_lossy(&output.stderr)
+    );
+    let stdout = String::from_utf8(output.stdout).unwrap();
+    let header = stdout.lines().next().unwrap_or_default();
+    assert!(!header.split_whitespace().any(|column| column == "target"));
+}
+
+#[test]
+fn single_target_custom_target_column_renders_positional_label() {
+    let server = start_echo_server(test_params(
+        Some(Duration::from_millis(30)),
+        Duration::from_millis(10),
+    ));
+    let target = server.addr.to_string();
+
+    let output = Command::new(env!("CARGO_BIN_EXE_irtt-cli"))
+        .args([
+            "--duration",
+            "30ms",
+            "--interval",
+            "10ms",
+            "--format",
+            "csv",
+            "--columns",
+            "target,seq",
+            "--header",
+            "never",
+            &target,
+        ])
+        .output()
+        .unwrap();
+
+    server.join();
+
+    assert!(
+        output.status.success(),
+        "status={:?}\nstderr={}",
+        output.status.code(),
+        String::from_utf8_lossy(&output.stderr)
+    );
+    let stdout = String::from_utf8(output.stdout).unwrap();
+    assert!(
+        stdout
+            .lines()
+            .any(|line| line.starts_with(&format!("{target},"))),
+        "{stdout}"
+    );
+}
+
 #[test]
 fn multi_target_csv_emits_rows_for_both_labels() {
     let params = test_params(Some(Duration::from_millis(40)), Duration::from_millis(10));