Payload for {:datamodel_init, %__MODULE__{}} - the datamodel's starting map, emitted once per Statifier.Interpreter.initialize/2, before the first <data> value is evaluated (plan decision 1).

datamodel is machine_state.datamodel as it stands after spec 5.3.3's unconditional <data> creation (Statifier.Interpreter.Datamodel.seed/2) and before the binding fold that follows it. That ordering is what makes this payload carry exactly the three contributions no {:datamodel_change, _} effect can ever describe: MachineState.new/2's :datamodel option, SystemVariables.initial/2's four spec 5.10 system variables, and the :undefined seed (ADR-0037's spelling) for every declared id. Taking the baseline after binding would restate values the per-<data> binding effects already carry (decision 1).

Emitted unconditionally, once, even for a chart with no <datamodel> at all (decision 2) - the four system variables mean the map is never empty, so a consumer always has a starting point with nothing to special-case.

Deliberately carries no binding, env_ids, or declared-id list: those are facts about the %Statifier.Machine{}, and docs/observability.md:94-115 constraint 3's model is that tooling resolves machine facts through the machine, not through an effect payload (decision 6). What this payload carries instead is values, which exist nowhere else - the environment's :datamodel option and the session's _sessionid are not recoverable from the machine alone.

datamodel is a term reference, not a deep copy - Elixir maps are immutable, so this struct costs one word, once per session, not O(datamodel size). Neither datamodel nor the :undefined atom inside it commits to a wire format: docs/observability.md:173-179 names "no wire format" as an explicit non-goal for this repo, and per ADR-0025 serialization is statifier-ui's own half of the mirror.