Review fixes: recorder Flush without panic; unreadable config file is an error

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

internal/config/unreadable_test.go

@@ -0,0 +1,47 @@
+package config_test
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.wntrmute.dev/kyle/crossbar/internal/config"
+)
+
+// A file that exists but cannot be read is an error, and not a validation error: nothing about
+// the configuration has been judged. Only a missing file is "absent" (and that is an error too).
+func TestUnreadableFileIsAnError(t *testing.T) {
+	if os.Geteuid() == 0 {
+		t.Skip("root can read a 000 file")
+	}
+	dir := t.TempDir()
+	path := filepath.Join(dir, "crossbar.toml")
+	good, err := os.ReadFile(filepath.Join("testdata", "good.toml"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, good, 0o000); err != nil {
+		t.Fatal(err)
+	}
+	_, err = config.Load(path)
+	if err == nil {
+		t.Fatal("Load on an unreadable file must fail")
+	}
+	if _, ok := config.IsError(err); ok {
+		t.Errorf("an unreadable file is not a validation *Error: %v", err)
+	}
+	if !strings.HasPrefix(err.Error(), "config: ") {
+		t.Errorf("Error() = %q, want the config: prefix", err.Error())
+	}
+}
+
+func TestDirectoryIsAnError(t *testing.T) {
+	_, err := config.Load(t.TempDir())
+	if err == nil {
+		t.Fatal("Load on a directory must fail")
+	}
+	if _, ok := config.IsError(err); ok {
+		t.Errorf("a directory is not a validation *Error: %v", err)
+	}
+}