feat(policy): add ValidWhitelistAddress

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/policy/policy_test.go

@@ -0,0 +1,18 @@
+package policy
+
+import "testing"
+
+func TestValidWhitelistAddress(t *testing.T) {
+	good := []string{"tk555@protonmail.com", "a.b@sub.example.co.uk", "@example.com", "@sub.example.com"}
+	for _, s := range good {
+		if err := ValidWhitelistAddress(s); err != nil {
+			t.Errorf("ValidWhitelistAddress(%q) = %v, want nil", s, err)
+		}
+	}
+	bad := []string{"", "   ", "notanaddress", "@", "@nodot", "a@nodot", "Bob <b@x.com>", "a@b@c.com"}
+	for _, s := range bad {
+		if err := ValidWhitelistAddress(s); err == nil {
+			t.Errorf("ValidWhitelistAddress(%q) = nil, want error", s)
+		}
+	}
+}