Optimize GraphQL subscription payloads for fractional market feeds

[Fatimasanusi]

Description

Broadcasting full vault objects over GraphQL subscriptions clogs bandwidth and causes rendering lag on mobile clients.

Architecture & Context

As detailed in GRAPHQL_SUBSCRIPTION_OPTIMIZATION.md, subscriptions must strictly utilize delta-payloads. Instead of sending the entire fractional order book, the backend should only publish the specific price diffs and share volume changes.

Technical Requirements

• Refactor subscription resolvers to emit isolated state changes.
• Implement a diffing algorithm between the previous and current block state.
• Ensure payload sizes do not exceed 2KB per tick.

Acceptance Criteria

• Network inspector confirms only delta data is transmitted over WSS.
• GraphQL payload size is reduced by at least 80%.
• Clients successfully reconstruct the full state using the deltas.