Use this first, before any generation or validation call, to discover the
exact ``message_type`` strings this server accepts (e.g.
``acmt.001.001.08`` Account Opening Instruction). Do not use it to fetch a
type's fields or schema -- call ``get_required_fields`` or
``get_input_schema`` for that.

Returns a list of ``{"message_type": ..., "name": ...}`` dictionaries, one
per supported message type (e.g. ``acmt.001.001.08``).

Use this for a quick checklist of the mandatory columns before building
account records. When you need full type/format constraints (not just
which fields are required), call ``get_input_schema`` instead.

Args:
    message_type: A supported ISO 20022 acmt message type.

Use this to learn every field, its type, and its constraints before
assembling records, or to drive a form/UI. For just the required-field
names use ``get_required_fields``; to actually check records against this
schema use ``validate_records``.

Args:
    message_type: A supported ISO 20022 acmt message type.

Use this before ``generate_message`` to catch structural/type errors per
record and get a row-by-row error report. This checks JSON-Schema shape
only; to validate a single financial identifier in isolation use
``validate_identifier``.

Returns a report ``{"valid": bool, "total": int, "valid_count": int,
"errors": [...]}``.

Args:
    message_type: A supported ISO 20022 acmt message type.
    records: One or more flat account records to validate.

Use this for a one-off identifier check with a clear pass/fail. To
validate identifiers embedded across a whole batch of account records,
prefer ``validate_records`` rather than calling this per field.

Returns ``{"kind": str, "value": str, "valid": bool}``.

Args:
    kind: One of ``"iban"``, ``"bic"``, or ``"lei"`` (case-insensitive).
    value: The identifier value to check.

This is the primary generation tool: pass account records you already
hold in memory and receive an XSD-validated XML document; no file is
written. Run ``validate_records`` first to surface record-level errors,
and ``list_message_types`` to confirm the ``message_type`` string.

Returns the validated XML document as a string, or an ``{"error": ...}``
payload (serialized) if generation fails.

Args:
    message_type: A supported ISO 20022 acmt message type.
    records: One or more flat account records.