Function symbol_to_counter_id 

pub fn symbol_to_counter_id(symbol: &str) -> String

Convert a user-supplied symbol (e.g. TSLA.US, 700.HK, .DJI.US, HSI.HK) to a counter_id (e.g. ST/US/TSLA, ST/HK/700, IX/US/.DJI, IX/HK/HSI).

Leading-dot symbols (e.g. .DJI.US) are US market indexes and always map to IX/. All other symbols are checked against the embedded ETF + index + warrant set and the remote-resolved cache; a matching entry is returned as-is. Unmatched symbols default to ST/.