A fixture bundle's events map (ADR-0003), turned into a sorted list of StatifierUI.EventInjection.Entry.t() a form can render as buttons.

build/1 accepts a StatifierUI.Fixtures.t() or nil. nil (or a bundle with no events at all) yields an empty palette with no diagnostics - the degraded mode StatifierUI.EventInjection turns into its free_form_only? flag.

Every entry's payload is encoded through StatifierUI.Value.encode/1 and then StatifierUI.Trace.Json.encode_to_string/1 - the same canonical, byte-stable JSON encoder the trace wire format uses, reused here because a Value.encode/1 result is exactly the "JSON-ready term" shape that encoder is typed against. Nothing about the trace wire format itself is touched; an injected event is an input, not a trace message.

A fixture event whose payload falls outside predicator's value domain (a tuple, a pid, a struct other than Date/DateTime) does not fail the whole build: the entry is omitted and a diagnostic is appended, in the same StatifierUI.Fixtures.diagnostic() shape a bundle itself already carries. One bad sample takes down one button, not the pane.

Atom-keyed payloads do not round-trip

StatifierUI.Fixtures validates scenario datamodels deeply but leaves event payloads verbatim, so a behaviour source can hand over an atom-keyed payload map. ADR-0005 says atom keys "serializ[e] as their names", which is exactly what StatifierUI.Trace.Json.encode_to_string/1 produces and what StatifierUI.Value.decode/1 reads back as strings. An entry's payload field keeps the atoms; its payload_text, and therefore any event actually sent from it, carries the string-keyed form. This is correct rather than lossy: the engine's datamodel is string-keyed, and a JSON sidecar could never have expressed the atoms in the first place.