Backend Control Plane

Brain's backend functions as a control plane that orchestrates all system components while never custodying user funds or private keys. It normalizes actions, enforces policy, routes execution, and indexes trust and payment data.

Core Services

Service	Responsibility
Auth Service	SIWX session management for users and agents
Agent Service	ERC-8004 agent lifecycle and configuration
Policy Engine	Evaluation and approval of actions and payments
Payment Orchestrator	x402 payment handling and UserOperation assembly
Execution Router	Routing calls to on-chain contracts or off-chain services
Trust Indexer	Aggregation and indexing of validation records and reputation

Full Execution Pipeline

1. Request received (from client, agent, or partner system)

2. Action normalized into a canonical representation

3. Authentication via SIWX and agent resolution via ERC-8004

4. Policy evaluation for the action and any associated PaymentIntent

5. If required, x402 payment handling is triggered

6. Execution router dispatches to the appropriate on-chain or off-chain target

7. UserOperation is submitted on-chain via ERC-4337 infrastructure

8. Results and receipts are recorded by the Trust Indexer and associated with agentId and policies

Core Data Objects

A consistent schema is maintained across all services:

• User — identity and session state

• Agent — agentId, execution address, metadata, status

• Account — smart account address, global policy hash

• Policy — structured constraint definitions

• PaymentIntent — x402 payment request state

• ValidationRecord — immutable action audit trail

The backend normalizes actions, enforces policy, routes execution, and indexes trust and payment data — but never holds private keys or funds. Custody remains entirely with user-controlled smart accounts.

Non-Custodial Design

The control plane is explicitly designed to be non-custodial:

• Private keys are never transmitted to or stored by the backend

• All signing happens client-side or within the agent's execution environment

• The backend issues policy approvals (signed proofs) but cannot unilaterally move funds

• Smart accounts enforce all constraints independently on-chain