=========
Why Frame
=========

CHILL, rings, cages, Steinhardt, and SOAP are per-snapshot. The
handle is one configuration: neighbours, a bonded graph, and labels
on that cloud.

One configuration
=================

``Frame`` is that handle. Multi-frame work is explicit:
``read(path, frame=n)`` (1-indexed) or ``frame.load_frame(n)`` on a
path-backed ``Frame``. Arrays-only and ASE-built frames have no path
and cannot ``load_frame``.

``Trajectory`` is an alias
==========================

``Trajectory`` is a compatibility alias of ``Frame``
(``src/pydseams/__init__.py``). It does not iterate a movie and does
not own a campaign. The engine CLI that walks trajectories and
writes ``output/`` lives in seams-core. This package does not grow a
second movie object.