Document Folder APIs and add local Visit Examples.

Co-authored-by: Cursor <cursoragent@cursor.com>

files.go

@@ -24,9 +24,13 @@ type Entry struct {
 
 // Folder is flat storage for one Working Folder (basenames only).
 type Folder interface {
+	// List returns first-level names in the Working Folder.
 	List() ([]Entry, error)
+	// Read returns the contents of a basename in the Working Folder.
 	Read(name string) ([]byte, error)
+	// Write creates or replaces a basename in the Working Folder.
 	Write(name string, data []byte) error
+	// Exists reports whether name is a non-directory file in the Working Folder.
 	Exists(name string) (bool, error)
 }
 
@@ -133,6 +137,7 @@ func LocalFolder(dir string) Folder {
 	return localFolder{dir: dir}
 }
 
+// List implements Folder for a local directory.
 func (f localFolder) List() ([]Entry, error) {
 	entries, err := os.ReadDir(f.dir)
 	if err != nil {
@@ -145,6 +150,7 @@ func (f localFolder) List() ([]Entry, error) {
 	return out, nil
 }
 
+// Read implements Folder for a local directory.
 func (f localFolder) Read(name string) ([]byte, error) {
 	if err := RequireBasename(name); err != nil {
 		return nil, err
@@ -152,6 +158,7 @@ func (f localFolder) Read(name string) ([]byte, error) {
 	return os.ReadFile(filepath.Join(f.dir, name))
 }
 
+// Write implements Folder for a local directory.
 func (f localFolder) Write(name string, data []byte) error {
 	if err := RequireBasename(name); err != nil {
 		return err
@@ -159,6 +166,7 @@ func (f localFolder) Write(name string, data []byte) error {
 	return os.WriteFile(filepath.Join(f.dir, name), data, 0o644)
 }
 
+// Exists implements Folder for a local directory.
 func (f localFolder) Exists(name string) (bool, error) {
 	if err := RequireBasename(name); err != nil {
 		return false, err