Webull's symbol mapping.

Native form is concatenated, no separator: BTCUSD. Canonical is BASE-QUOTE. So both directions do real work, and the same overlapping-quote hazard applies as on any sep: "" venue — the quote list is consulted in order, and a shorter quote that is also the tail of a longer one wins if checked first.

USDT and USDC therefore precede USD. Without that, BTCUSDT splits as BTCUS/DT or BTCUSD/T depending on the list, and neither is an asset.

Why both directions run through CanonicalPair

So they cannot drift. The adapter this came from records why that matters: an audit found build_order_body sending the canonical symbol to the venue un-converted, so reads worked and writes silently did not. Running every path — read and write — through one mapping is the fix, and it only works if there is exactly one mapping.