Review API reference and requirements for Blockchain and LEZ integration

[fryorcraken]

Write RFPs defining how third parties integrate the two chains — wallets,
centralised exchanges, custodians, payment gateways, data and price
aggregators, node and RPC providers, fiat on/off ramps, bridges, and tax and
accounting providers. The CEX is the reference integrator profile.

Split per chain, because the two expose different shapes.

logos-blockchain (L1)

• Blockchain API as FFI bindings — one surface covering both read and
  signing, with enterprise integration in mind, expected to be documented.
  See https://github.com/logos-co/logos-api-sdk-research. (internal) — [Internal RFP] Blockchain API — FFI Bindings #219
• JSON-RPC proxy module + SDK (TypeScript? TBC) to expose and consume that
  API. Merged into one RFP: no reason to award them to separate teams.
  (internal) — [Internal RFP] JSON-RPC Proxy Module & TypeScript SDK for Blockchain API #220

LEZ

Unlike L1, LEZ splits the read surface (indexer) from key handling and signing
(wallet), so there is no single combined API surface. Per
logos-co/rfp#200 this is a six-deliverable suite, five
of them LEZ-specific:

• Indexer FFI — the node API, in the sense the eth namespace is on
  Ethereum's JSON-RPC. Answers what happened and what the current state is;
  signs nothing. RFP-027. (internal) — [Internal RFP] LEZ Node API #235
• Wallet FFI — key handling, derivation, and signing. Also owns
  transaction simulation, which the indexer cannot provide. (internal) — [Internal RFP] LEZ Wallet API: key handling, derivation, proving, and signing #236
• JSON-RPC proxy module over both FFI surfaces. (external) — [RFP] LEZ JSON-RPC Proxy Module & Client Library #237
• Wallet SDK — the per-language library a wallet is built from,
  BDK-shaped. Not the Provider SDK a dApp calls to ask a wallet to sign.
  (external) — [RFP] LEZ-DK: The LEZ Development Kit #238
• Indexer SDK — client library for the indexer's JSON-RPC surface.
  (external) — [RFP] LEZ Indexer Client Library #239

Both chains

• Other interface modules and external SDKs — gRPC, GraphQL, Mesh/Rosetta
  adapter; SDKs beyond TypeScript (Rust? TBC). Cross-chain work, scoped once
  rather than duplicated per chain. (external) — [RFP] Additional Interface Modules & External SDKs (gRPC, GraphQL, Mesh, Rust) #222