Rejects requests whose selection expands to too many source identifiers.

Whether the selection comes from a POST body (one line per stream) or from GET query parameters (comma/space separated networks, stations, channels), the resulting set of selected source identifiers must stay within a configurable cap so a single request cannot trigger unbounded database and data-reading work.

The limit is configured via the WSDATASELECT_MAX_SOURCE_IDENTIFIERS environment variable (default 200).