Space keeps its scans and refreshes them: zfs diff, folder mtimes, resume after cancel

A scan is saved beside the config and read back after a restart. The next scan starts
from it: on a pool with snapshots zfs diff names what changed and only those folders are
read; elsewhere a folder whose mtime is unchanged keeps its list and only its kept files
are stat'ed again. A cancelled scan keeps what it walked and Resume reads the rest.
Forget drops the saved result. The treemap is every file a tile, grouped by folder, with
no nested boxes: the folder chains of a Linux system made a staircase of empty headers.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/api/server.go

@@ -85,11 +85,11 @@ type Server struct {
 func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *metrics.Collector, st *store.Store, svc *services.Manager, cr *cron.Manager, tm *tasks.Manager, up *updates.Manager, sto *storage.Manager, fsLocal, fsSudo files.FS, nm *nodes.Manager, fingerprint string, ui fs.FS, version string) *Server {
 	s := &Server{cfg: cfg, sessions: sessions, mgr: mgr, metrics: col, sensors: sensors.NewRegistry(col), store: st, svc: svc, cron: cr, tasks: tm, updates: up, storage: sto, fsLocal: fsLocal, fsSudo: fsSudo, nodes: nm, fingerprint: fingerprint, ui: ui, version: version,
 		started: time.Now(), user: os.Getenv("USER")}
-	if self, err := os.Executable(); err == nil {
-		s.space = space.New(self)
-	} else {
-		s.space = space.New("hamlab")
+	self, err := os.Executable()
+	if err != nil {
+		self = "hamlab"
 	}
+	s.space = space.New(self, filepath.Join(cfg.DataDir(), "space"))
 	s.hostName() // read it once now so the first request doesn't have to
 	if u, err := user.Current(); err == nil && u.Username != "" {
 		s.user = u.Username
@@ -260,6 +260,7 @@ func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *me
 	m.HandleFunc("GET /api/space/{disk}", s.auth(s.spaceStatus))
 	m.HandleFunc("POST /api/space/{disk}/scan", s.auth(s.spaceScan))
 	m.HandleFunc("POST /api/space/{disk}/cancel", s.auth(s.spaceCancel))
+	m.HandleFunc("DELETE /api/space/{disk}", s.auth(s.spaceForget))
 	m.HandleFunc("GET /api/space/{disk}/tree", s.auth(s.spaceTree))
 	m.HandleFunc("GET /api/space/{disk}/largest", s.auth(s.spaceLargest))
 	m.HandleFunc("GET /api/procs", s.auth(s.procList))