Core Concepts

Guards and Policy

What guards are

Guards are deterministic policy checks evaluated before state advancement.
In this runtime, a guard is a GuardFunction returning { passed, code?, message?, metadata? }.

Hard vs soft

| | Hard | Soft | |---|---|---| | Blocks transition | Yes | No | | State advances | No | Yes | | Emitted event on failure | loop.guard.failed | Failure warning is attached to _softGuardWarnings evidence | | Typical use | Mandatory policy | Warning and monitoring |

evaluatedBy

GuardSpec.evaluatedBy:

• runtime - evaluated by registered GuardFunction
• module - declared for module-level policy contract
• external - caller provides result context in evidence contract

Built-in guards

actor_has_permission

• Reads: required_role, roles
• Fails when required_role is missing from roles

approval_obtained

• Reads: approved
• Fails when approved !== true

deadline_not_exceeded

• Reads: deadline_iso
• Fails when deadline format is invalid or current time exceeds deadline

duplicate_check_passed

• Reads: duplicate_found
• Fails when duplicate_found === true

field_value_constraint

• Reads: constraint plus referenced field
• Supported operators: eq, gt, lt, in

Add a custom guard

1import { guardId } from '@loop-engine/core'
2import { createGuardRegistry } from '@loop-engine/guards'
3 
4const registry = createGuardRegistry()
5registry.register(guardId('my_custom_guard'), async (context) => {
6  const passed = context.evidence.budget_available === true
7  return {
8    passed,
9    message: passed ? 'Budget available' : 'Insufficient budget'
10  }
11})

Use this registry in createLoopSystem({ loops, guards: registry }).

Related

• Decision Governance
• Human Approval Gates