Extract Files seam, WebDAV, and Visit from CheckDNS.

Publish go-nc-files v1 with local/WebDAV Root, DefaultPathStore, and
neutral Working Folder language; depends on go-nc-exapp v0.1.0.

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

visit.go

@@ -0,0 +1,93 @@
+package goncfiles
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Visit is one ExApp opening: Working Folder for this request plus the Saved Default.
+type Visit struct {
+	SavedDefault  string
+	WorkingRel    string
+	VisitRelative string
+	FS            Folder
+	defaults      DefaultPathStore
+	root          Root
+}
+
+// Open resolves the Working Folder for this visit.
+// initialFolderName is used when no Saved Default is stored yet (app-icon first launch).
+// visitRelative empty means app-icon launch (Saved Default, creating the initial folder empty if missing).
+// A Files-view folder is used only for this visit and does not change the Saved Default.
+// Missing or forbidden visit paths fail closed (no create, no fallback).
+func Open(root Root, defaults DefaultPathStore, initialFolderName, visitRelative string) (*Visit, error) {
+	saved, err := defaults.GetDefault()
+	if err != nil {
+		return nil, err
+	}
+	if saved == "" {
+		saved = initialFolderName
+	}
+	if CleanRel(saved) == "" {
+		return nil, fmt.Errorf("invalid saved Working Folder path")
+	}
+
+	raw := strings.Trim(strings.ReplaceAll(visitRelative, "\\", "/"), "/")
+	v := &Visit{
+		SavedDefault: saved,
+		defaults:     defaults,
+		root:         root,
+	}
+
+	if raw == "" {
+		fs, err := root.EnsureFolder(saved)
+		if err != nil {
+			return nil, err
+		}
+		v.WorkingRel = saved
+		v.FS = fs
+		return v, nil
+	}
+
+	rel := CleanRel(raw)
+	if rel == "" {
+		return nil, fmt.Errorf("invalid Working Folder path")
+	}
+	v.VisitRelative = rel
+	fs, err := root.OpenFolder(rel)
+	if err != nil {
+		return nil, fmt.Errorf("Working Folder %q: %w", rel, err)
+	}
+	v.WorkingRel = rel
+	v.FS = fs
+	return v, nil
+}
+
+// OpenLocal is the local-adapter convenience: files root + settings JSON.
+func OpenLocal(filesRoot, settingsPath, initialFolderName, visitRelative string) (*Visit, error) {
+	return Open(Local{RootDir: filesRoot}, FileStore{Path: settingsPath}, initialFolderName, visitRelative)
+}
+
+// SetDefault persists a new Saved Default and ensures the folder exists.
+func (v *Visit) SetDefault(relative string) error {
+	rel := CleanRel(relative)
+	if rel == "" {
+		return fmt.Errorf("invalid Saved Default path")
+	}
+	if _, err := v.root.EnsureFolder(rel); err != nil {
+		return err
+	}
+	if err := v.defaults.SetDefault(rel); err != nil {
+		return err
+	}
+	v.SavedDefault = rel
+	return nil
+}
+
+// WorkingDir returns a local absolute path when using the local adapter; otherwise WorkingRel.
+func (v *Visit) WorkingDir() string {
+	if p, ok := LocalPath(v.FS); ok {
+		return p
+	}
+	return v.WorkingRel
+}