cli: simplify option model per pike review

- appendList: one home for the List newline-join rule (was duplicated
  across accumulate and set)
- fold the redundant Int64 getter into Int; drop the truthy helper for
  the shared boolWord vocabulary
- add Opt.Metavar so help derives the value placeholder from data
  instead of branching on the option name (seed-time)

No behavior change; --help output is byte-identical.

cli/parse.go

@@ -41,7 +41,7 @@ func Parse(args []string) (*Result, error) {
 	opts := newOptions()
 	applyDefaults(opts)
 
-	if !truthy(cmdVals["no-conf"]) {
+	if noConf, _ := boolWord(cmdVals["no-conf"]); !noConf {
 		explicit := cmdVals["conf-path"]
 		path, fromUser := confPath(explicit)
 		if err := applyConfig(opts, path, fromUser); err != nil {
@@ -138,14 +138,23 @@ func parseArgs(args []string) (vals map[string]string, uris []string, action Act
 // accumulate stores a value, joining repeatable List options with newlines.
 func accumulate(vals map[string]string, o *Opt, val string) {
 	if o.Kind == List {
-		if prev, ok := vals[o.Long]; ok {
-			vals[o.Long] = prev + "\n" + val
-			return
-		}
+		vals[o.Long] = appendList(vals[o.Long], val)
+		return
 	}
 	vals[o.Long] = val
 }
 
+// appendList is the single home of the List newline-join rule, shared by the
+// raw-parse layer (accumulate) and the resolved layer (set). An empty prev (the
+// option not yet seen) yields val unchanged, so the first value carries no
+// leading newline.
+func appendList(prev, val string) string {
+	if prev == "" {
+		return val
+	}
+	return prev + "\n" + val
+}
+
 func applyDefaults(o *Options) {
 	for i := range options {
 		opt := &options[i]
@@ -215,10 +224,8 @@ func set(o *Options, name, val string) error {
 	if err := validate(opt, val); err != nil {
 		return err
 	}
-	if opt.Kind == List {
-		if prev, ok := o.vals[name]; ok && o.set[name] {
-			val = prev + "\n" + val
-		}
+	if opt.Kind == List && o.set[name] {
+		val = appendList(o.vals[name], val)
 	}
 	o.vals[name] = val
 	o.set[name] = true
@@ -304,8 +311,3 @@ func confPath(explicit string) (path string, fromUser bool) {
 	}
 	return filepath.Join(home, ".config", "got", "got.conf"), false
 }
-
-func truthy(s string) bool {
-	val, _ := boolWord(s)
-	return val
-}