Shared x402/EIP-712 platform SDK plumbing — auth, payment, usage, error, and retry handling —
extracted from @agentkv/client for reuse across future agentx402 service SDKs.
@agentkv/client re-exports this package's AgentXError as AgentKVError, so both names refer
to the same class object and instanceof AgentKVError holds across the dependency graph. This relies on
a single resolved copy of @agentx402-ai/core — if a downstream project ever resolves two
incompatible majors of it (e.g. one dependency pinning ^0.1.0 and another ^1.0.0), each copy's
AgentXError is a distinct class, and instanceof checks silently fail across them.
MIT