Chain-specific protocol fields. Solana SPL tokens carry tokenProgram (+ an
optional mintfx mapping); other chains carry neither. No longer discriminated
on the chain — the chain is now the chain_id FK and validity is enforced at
the FK + service layer.
Chain-specific protocol fields. Solana SPL tokens carry
tokenProgram(+ an optional mintfx mapping); other chains carry neither. No longer discriminated on the chain — the chain is now thechain_idFK and validity is enforced at the FK + service layer.