feat: Implement Autonomy Gate Engine (T1/T2/T3 classifier)

[dcplatforms]

Overview

Implement the Autonomy Gate Engine — classifies every proposed agent action by risk tier and routes accordingly.

Spec: docs/ARCHITECTURE.md §3

Implementation

• AutonomyGate class in src/orchestrator/autonomy_gate/
• Risk classifier: LOW → T3, MEDIUM → T2, HIGH → T1
• T3: execute + log
• T2: push to Human Approval Queue, block until approved or timeout
• T1: return advisory text only, never execute
• Confidence score threshold enforcement (T3 requires >= 0.92)

Tests Required

• LOW risk + high confidence → T3 execute
• MEDIUM risk → T2 queue + await approval
• HIGH risk → T1 advisory only, verify no tool execution
• T1 tool invocation attempt → block + alert