Which Webull this package is talking to — production, or the UAT environment.

This venue's demo story is only half a story, and that half matters

Gemini's demo environment is a complete parallel exchange: REST and streaming both. This one is not.

The prior adapter records the measurement that establishes it: mqtt-uat.webullbroker.com → NXDOMAIN. There is no UAT broker to connect to, and no amount of configuration produces one.

So environment: :uat gives a consumer authenticated REST against test data and no live stream at all. That is a genuinely useful thing — order placement and account calls can be exercised without money — and it is also a trap if a package pretends otherwise. subscribe/2 in UAT does not silently fall back to production, because a consumer testing against UAT who received production prices would be reading real market data while believing it was fake. It refuses.

streaming?/1 exists so a caller can ask before it commits, rather than discovering the gap from a subscription that never delivers.

Resolution order

1. an explicit :environment in the call's options — wins always
2. DpExchange.Core.Config, which resolves per process, so one async test or one strategy runner can sit in UAT while its neighbours do not
3. :production

Production is the default and an unrecognised value raises. A typo must not quietly resolve to production: the failure is asymmetric, since meaning UAT and getting production sends a real order to a real broker.