Document the exported message.Message.String and message.Message.Usage accessors

message/content.go

@@ -90,7 +90,8 @@ func unmarshalRawContent(data json.RawMessage) (Content, error) {
 	return &raw, nil
 }
 
-// Text returns the first text content in the response, or empty string.
+// Text returns the concatenated text of all TextContent in the response,
+// or empty string if there is none.
 func (cs Contents) Text() string {
 	var sb strings.Builder
 	for _, c := range cs {

message/message.go

@@ -61,10 +61,14 @@ func NewText(text string) *Message {
 	return New(&TextContent{Text: text})
 }
 
+// String implements fmt.Stringer, returning the concatenated text of all
+// TextContent in the message (delegating to Contents.Text).
 func (m *Message) String() string {
 	return m.Contents.Text()
 }
 
+// Usage returns the aggregated UsageDetails carried by the message's
+// UsageContent (delegating to Contents.Usage).
 func (m *Message) Usage() UsageDetails {
 	return m.Contents.Usage()
 }