ParamResolution

One declared input, resolved for one client. ``source_category`` (S2-read §3) is the authoritative 4-way classification for FILE inputs (``carried_forward|synced|uploaded|missing``) and ``null`` for scalar inputs (resolved at launch, never client-sourced). ``status`` (``sourced``/``missing``) is a back-compat shim: ``missing`` iff ``source_category`` is ``missing``, else ``sourced``; scalars report ``missing`` with a null ``source``.