demand-control-dynamic-max-cost.md

@graphql-hive/gateway-runtime	minor

Allow maxCost in DemandControlPluginOptions to accept a function for dynamic cost limiting.

Previously, maxCost only accepted a static number. It now also accepts a synchronous or asynchronous function (payload: DemandControlMaxCostPayload) => MaybePromise<number>, where payload contains:

• operationCost – the estimated cost of the current subgraph operation
• totalCost – the accumulated cost for the whole request context so far
• subgraphName – the name of the subgraph being executed
• executionRequest – the full execution request object

This lets you implement per-user rate limits, per-subgraph budgets, or any other context-aware cost policy. The DemandControlMaxCostPayload interface is exported from the package for use when typing your maxCost function.