Document every exported symbol and how callers use the library.

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

webdav.go

@@ -14,6 +14,8 @@ import (
 )
 
 // WebDAVRoot is a User Files Root at /remote.php/dav/files/{user}/.
+// Cred supplies the user id and AppAPI auth headers.
+// A nil Client uses http.DefaultClient.
 type WebDAVRoot struct {
 	Cred   gonexapp.Credentials
 	Client *http.Client
@@ -48,6 +50,10 @@ func (r WebDAVRoot) urlFor(rel string) (string, error) {
 }
 
 // OpenFolder opens an existing folder via WebDAV PROPFIND.
+// It does not create the folder.
+// It returns an error wrapping ErrNotExist when the server responds 404,
+// ErrForbidden on 401 or 403, and ErrNotDir when the resource is not a collection.
+// An invalid rel returns a plain error and does not call the server.
 func (r WebDAVRoot) OpenFolder(rel string) (Folder, error) {
 	clean := CleanRel(rel)
 	if clean == "" {
@@ -63,7 +69,9 @@ func (r WebDAVRoot) OpenFolder(rel string) (Folder, error) {
 	return webdavFolder{root: r, rel: clean}, nil
 }
 
-// EnsureFolder creates the folder (and parents) with MKCOL, then opens it.
+// EnsureFolder creates the folder and missing parents with MKCOL, then opens it.
+// It returns an error wrapping ErrForbidden on 401 or 403, or a plain error
+// when rel is invalid or MKCOL fails for another status.
 func (r WebDAVRoot) EnsureFolder(rel string) (Folder, error) {
 	clean := CleanRel(rel)
 	if clean == "" {