State Production: Write-Through Current State Cache

[aristidesstaffieri]

Summary

Implement an in-memory write-through cache for protocol current state during live ingestion, enabling efficient computation of additive state after handoff from migration.

Scope

• Per-protocol cache: map[protocolID] -> { currentStateCursor, stateData }
• Empty at start: cache is unpopulated when live ingestion starts
• Populated from DB: on first successful CAS-advance of current_state_cursor (the handoff moment), read current state from protocol state tables (one-time DB read)
• Updated per ledger: on each subsequent ledger, update cache in-memory + write through to DB
• Lost on restart: if live ingestion restarts, cache is repopulated from DB on next current-state production
• Needed because additive state (e.g., token balances) requires knowing state at N-1 to compute state at N

Dependencies

• State Production: Live Ingestion State Production with Per-Protocol Dual CAS Gating #514 (Live Ingestion State Production with Per-Protocol Dual CAS Gating)

Reference

docs/feature-design/data-migrations.md (State Production section, line 619+)