@spec apply_mappings(term(), map(), keyword() | map()) ::
  {:ok, struct() | [struct()]} | {:error, term()}

Applies a v4 normalization mapping to raw response data.

@spec parse(term(), map() | nil, module(), keyword()) ::
  {:ok, struct() | [struct()]} | {:error, term()}

Parses data against a single normalization-slot mapping into target.

This is the runtime entry point for the generated per-exchange parse_* functions (parse_ticker/2, parse_trade/2, …). It applies the Honesty Rule to the upstream Phase 12 field maps before delegating to apply_mappings/3:

• nil slot (upstream never derived a field map) → {:error, :no_field_map}
• non-nil _unresolved_reason (upstream flagged the slot as not safely derivable) → {:error, {:unresolved, reason}} — the partial field map is not applied, so callers never receive a struct silently built from an incomplete mapping
• resolved slot with a non-empty field_map or branches → parsed

opts may carry :market (a market-info map), :symbol, and :currencies (the loaded currency catalog); all are threaded into the parser context.

Examples

iex> Bourse.Parser.parse(%{}, nil, Bourse.Ticker)
{:error, :no_field_map}

iex> Bourse.Parser.parse(%{}, %{"_unresolved_reason" => "identifier_return"}, Bourse.Market)
{:error, {:unresolved, "identifier_return"}}