Vendored subset of the upstream counter.rs directory:
special counter_ids known at build time (ETFs, US indexes, US warrants).
New listings resolved at runtime go through Longbridge.Symbol.Cache.
Summary
Functions
Looks up a user symbol against the embedded directory. Returns the
counter_id (e.g. "ETF/US/SPY") on hit, nil otherwise.
Functions
Looks up a user symbol against the embedded directory. Returns the
counter_id (e.g. "ETF/US/SPY") on hit, nil otherwise.
Does not apply the default ST/ fallback — callers should do that
themselves so the priority order (ST/, IX/, ETF/, WT/) matches
the upstream.