feat(cli): classify every provisioning failure with stable codes

cmd/cli/hostname_test.go

@@ -33,3 +33,65 @@ func Test_validHostname(t *testing.T) {
 		})
 	}
 }
+
+// TestOffendingHostnameChars pins the characters surfaced in the
+// CUSTOM_HOSTNAME_INVALID message, so the failure names what is actually
+// wrong instead of a bare "invalid hostname".
+func TestOffendingHostnameChars(t *testing.T) {
+	tests := []struct {
+		name     string
+		hostname string
+		want     string
+	}{
+		{"single offender", "foo@bar", "@"},
+		{"space", "foo bar", " "},
+		{"dot is allowed", "foo.bar", ""},
+		{"hyphen is allowed", "foo-bar", ""},
+		{"distinct offenders in order", "a!b!c#d", "!#"},
+		{"structurally invalid but no bad char", strings.Repeat("a", 65), ""},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := offendingHostnameChars(tc.hostname); got != tc.want {
+				t.Errorf("offendingHostnameChars(%q) = %q, want %q", tc.hostname, got, tc.want)
+			}
+		})
+	}
+}
+
+// TestHostnameMayBeFoldedByServer pins the characters ControlD's
+// DevicesTableModel.formatDeviceName folds or strips when it registers a
+// device, so a ctrld-accepted name using one gets a heads-up notice instead
+// of silently registering under a different name.
+func TestHostnameMayBeFoldedByServer(t *testing.T) {
+	tests := []struct {
+		name     string
+		hostname string
+		want     bool
+	}{
+		{"dot", "foo.bar", true},
+		{"space", "foo bar", true},
+		{"plus", "foo+bar", true},
+		{"plain", "foobar", false},
+		{"hyphen only", "foo-bar", false},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := hostnameMayBeFoldedByServer(tc.hostname); got != tc.want {
+				t.Errorf("hostnameMayBeFoldedByServer(%q) = %v, want %v", tc.hostname, got, tc.want)
+			}
+		})
+	}
+}
+
+// TestCustomHostnameFailureMessage pins the message shape the T6 contract
+// requires: the flag/field name, the offending character(s), and the
+// allowed format.
+func TestCustomHostnameFailureMessage(t *testing.T) {
+	msg := customHostnameFailureMessage("foo@bar")
+	for _, want := range []string{"--custom-hostname", "CustomHostname", "@", "allowed format"} {
+		if !strings.Contains(msg, want) {
+			t.Errorf("customHostnameFailureMessage() = %q, want it to contain %q", msg, want)
+		}
+	}
+}