fix session.All/Get to use rootState.sessions map

All() and Get() were looking at root.Children() (mounted child trees)
but sessions are stored in rootState.sessions. They were never mounted
as children, so All() always returned empty — breaking D-Bus ListSessions
and WatchExisting, causing the KDE GUI to see no restored sessions.

session/session.go

@@ -1,31 +1,25 @@
 // Package session builds the session/ file tree for the 9P namespace.
-// The tree IS the session collection — sessions are mounted children.
-// No manager, no store. Package functions for lifecycle.
+// The tree IS the session collection — rootState holds the sessions map.
+// Package functions for lifecycle, lookup, and enumeration.
 package session
 
 import (
 	"olliesrv/fs"
 )
 
-// Get returns the Session mounted at id, or nil.
+// Get returns the Session for id, or nil.
 func Get(root *fs.Tree, id string) *Session {
-	child := root.Child(id)
-	if child == nil {
-		return nil
-	}
-	if sess, ok := child.Data.(*Session); ok {
-		return sess
-	}
-	return nil
+	return Lookup(root, id)
 }
 
-// All returns all mounted sessions.
+// All returns all active sessions.
 func All(root *fs.Tree) []*Session {
-	var sessions []*Session
-	for _, child := range root.Children() {
-		if sess, ok := child.Data.(*Session); ok {
+	rs := state(root)
+	rs.mu.RLock()
+	defer rs.mu.RUnlock()
+	sessions := make([]*Session, 0, len(rs.sessions))
+	for _, sess := range rs.sessions {
 		sessions = append(sessions, sess)
 	}
-	}
 	return sessions
 }