The symbol-normalisation contract every venue package must satisfy.

A venue's SymbolFormat module @behaviours this so the contract is obligatory: a package that ships without both directions of the conversion fails the compiler's missing-callback check. This is what makes the multi-exchange promise safe — one caller's canonical BASE-QUOTE pairs mean the same thing on every venue, because every venue is forced to round-trip them through the shared DpExchange.Core.CanonicalPair normaliser with its own mapping.

Two directions, both total (never raise — malformed input degrades to "UNKNOWN" for the inbound direction so a bad feed message can't crash a parser):

• to_canonical_symbol/1 — exchange-native → canonical BASE-QUOTE (uppercase, dash). The form the rest of the system stores and reasons about.
• to_exchange_symbol/1 — canonical BASE-QUOTE → exchange-native. The form a connector puts on the wire (orders, subscriptions).

Venues with more than one native channel — a WebSocket vocabulary differing from the REST one is common — implement these two against their account/REST form — the authoritative native form for orders and balances — and expose channel-specific helpers alongside.