[relay] Phase 4 — SageBot integration: payload schemas, Dexter MCP, x402 auth

[Dipraise1]

Context

Relay core (Phases 1–2) and reliability (DLQ, status reporting) are shipped. The consumer side — SageBot on XERIS — is not wired up yet.

Tasks

• Define XERIS payload schema for each Engram output type (memory, inference, ranking)
• Wire Dexter MCP tool calls into the relay flow
• x402 auth on relay submissions so XERIS knows who is paying for compute
• SageBot receives Engram outputs as external_intelligence context

From TASKS.md — Relay Phase 4.