coverage: easy-wins batch across cli, system, paths, vmdns, toolingplan

Pure-Go tests for formatters, layout resolution, and validators — no
fixtures, no external processes. Targets previously-zero functions the
triage scan flagged as low-hanging fruit.

  cli          55% -> 65%
  paths        64% -> 91%
  system       65% -> 75%
  vmdns        72% -> 86%
  toolingplan  73% -> 78%

Total 52.6% -> 54.0%.

internal/vmdns/remove_test.go

@@ -0,0 +1,93 @@
+package vmdns
+
+import (
+	"testing"
+)
+
+func TestServerRemoveDropsRecord(t *testing.T) {
+	server := startTestServer(t)
+	if err := server.Set("devbox.vm", "172.16.0.8"); err != nil {
+		t.Fatalf("Set: %v", err)
+	}
+	if _, ok := server.Lookup("devbox.vm"); !ok {
+		t.Fatal("record missing before remove")
+	}
+
+	if err := server.Remove("devbox.vm"); err != nil {
+		t.Fatalf("Remove: %v", err)
+	}
+	if _, ok := server.Lookup("devbox.vm"); ok {
+		t.Fatal("record still present after Remove")
+	}
+}
+
+func TestServerRemoveInvalidNameIsNoop(t *testing.T) {
+	server := startTestServer(t)
+	// Non-.vm names silently normalize-fail, returning nil.
+	if err := server.Remove("example.com"); err != nil {
+		t.Fatalf("Remove: %v", err)
+	}
+}
+
+func TestServerRemoveNilReceiver(t *testing.T) {
+	var s *Server
+	if err := s.Remove("anything.vm"); err != nil {
+		t.Fatalf("nil Remove: %v", err)
+	}
+}
+
+func TestServerSetRejectsIPv6(t *testing.T) {
+	server := startTestServer(t)
+	if err := server.Set("six.vm", "::1"); err == nil {
+		t.Fatal("expected error for IPv6 address")
+	}
+}
+
+func TestServerSetRejectsBadIP(t *testing.T) {
+	server := startTestServer(t)
+	if err := server.Set("bad.vm", "not-an-ip"); err == nil {
+		t.Fatal("expected parse error for bogus IP")
+	}
+}
+
+func TestServerSetRejectsNonVMName(t *testing.T) {
+	server := startTestServer(t)
+	if err := server.Set("example.com", "172.16.0.1"); err == nil {
+		t.Fatal("expected error for non-.vm name")
+	}
+}
+
+func TestServerReplaceRejectsBadIP(t *testing.T) {
+	server := startTestServer(t)
+	err := server.Replace(map[string]string{"bad.vm": "nope"})
+	if err == nil {
+		t.Fatal("expected parse error")
+	}
+}
+
+func TestServerReplaceRejectsIPv6(t *testing.T) {
+	server := startTestServer(t)
+	err := server.Replace(map[string]string{"six.vm": "::1"})
+	if err == nil {
+		t.Fatal("expected IPv6 rejection")
+	}
+}
+
+func TestServerNilLookupAndAddr(t *testing.T) {
+	var s *Server
+	if _, ok := s.Lookup("x.vm"); ok {
+		t.Fatal("nil Lookup should return false")
+	}
+	if got := s.Addr(); got != "" {
+		t.Fatalf("nil Addr = %q, want empty", got)
+	}
+	if err := s.Close(); err != nil {
+		t.Fatalf("nil Close: %v", err)
+	}
+	if err := s.Set("x.vm", "172.16.0.1"); err != nil {
+		t.Fatalf("nil Set: %v", err)
+	}
+	if err := s.Replace(map[string]string{"x.vm": "172.16.0.1"}); err != nil {
+		t.Fatalf("nil Replace: %v", err)
+	}
+}