fleetd#222: fix currentUserGroup() to resolve the real primary group (fleetd#225)

The helper I copied from OpenCodeLauncherTest read the CWD's owning
group instead of the process's real primary group, so it silently
picked up whatever group owns the directory Maven was started from
(staff in a home checkout, wheel under /private/tmp on macOS) rather
than a group the operator is actually in. Replaced with the id -gn
based resolution that landed on #230 for the other two copies of this
helper, same shape and skip wording.

fleetd/src/test/java/dev/ltms/fleet/member/ClaudeCodeLauncherTest.java

@@ -23,7 +23,6 @@ import org.slf4j.LoggerFactory;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.nio.file.attribute.PosixFileAttributeView;
 import java.nio.file.attribute.PosixFilePermissions;
 import java.util.List;
 import java.util.Map;
@@ -1802,11 +1801,37 @@ class ClaudeCodeLauncherTest {
                 0, System::currentTimeMillis, () -> { }, null, null, null, config);
     }
 
-    /** The current process's own primary group — resolvable on whatever host runs this test. */
-    private static String currentUserGroup() throws IOException {
-        PosixFileAttributeView view = Files.getFileAttributeView(Path.of("."), PosixFileAttributeView.class);
-        assumeTrue(view != null, "this host's filesystem does not support POSIX group ownership");
-        return view.readAttributes().group().getName();
+    /**
+     * The current process's REAL primary group — resolved via {@code id -gn}, never by reading a
+     * directory's owning group (fleetd #225). Those two coincide only by accident: a directory's
+     * group is whichever group happened to own the path Maven was started from — {@code staff} in
+     * a home checkout, {@code wheel} under {@code /private/tmp} on macOS — and the fix-up this test
+     * exercises then fails for real when the operator is not a member of that borrowed group,
+     * exactly the case {@code assumeTrue(view != null, ...)} never covered (it only detects a
+     * filesystem with no POSIX groups at all, not a resolvable-but-wrong one). Skips (never fails)
+     * when {@code id} is unavailable or its primary group cannot be resolved on this host.
+     */
+    private static String currentUserGroup() {
+        String out;
+        boolean ok;
+        try {
+            Process p = new ProcessBuilder("id", "-gn").redirectErrorStream(true).start();
+            try (java.io.BufferedReader r = new java.io.BufferedReader(
+                    new java.io.InputStreamReader(p.getInputStream(), java.nio.charset.StandardCharsets.UTF_8))) {
+                out = r.lines().collect(java.util.stream.Collectors.joining("\n")).trim();
+            }
+            ok = p.waitFor(5, java.util.concurrent.TimeUnit.SECONDS) && p.exitValue() == 0 && !out.isBlank();
+        } catch (IOException e) {
+            out = null;
+            ok = false;
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            out = null;
+            ok = false;
+        }
+        assumeTrue(ok, "cannot resolve this process's real primary group via `id -gn` on this host "
+                + "— skipping a POSIX-group-dependent test rather than failing it");
+        return out;
     }
 
     /**