Unprivileged read-only interface for observing active sessions. Sent once when the manager is first created. May be an empty array. Broadcast to all connected clients when any session is created. Broadcast to all connected clients when any session is destroyed. Creates a `session_core_session` object for the given session_id. The daemon immediately pushes all fields, followed by done. If the session does not exist, destroyed is sent instead. Creates a session_core_session object for the session whose leader PID matches the given pid. The daemon immediately pushes all fields, followed by done. If no matching session exists, destroyed is sent instead. Creates a session_core_session object for the session whose user ID matches the given uid. The daemon immediately pushes all fields, followed by done. If no matching session exists, destroyed is sent instead. Creates a session_core_user object for the given uid. The daemon immediately pushes all fields, followed by done. If uid does not correspond to a known user, not_found is sent instead. Provides information about a single session. All fields are pushed immediately on creation and re-sent if they change. Sent when the session is destroyed or if the `session_id` passed to `get_session` was not found. The client should release this object. Provides information about a single user, identified by uid. All fields are pushed immediately on creation, followed by done. Reflects whether the user currently has sessions and whether any of them is in the foreground, combined with the lingering flag. Re-sent whenever it changes. Sent when the uid passed to get_user does not correspond to a known user. The client should release this object. Persists the lingering flag so it survives across sessions. Requires root, or that the caller's uid matches this user's uid.