Minimal host-facing agent runtime.
AgentEngine intentionally exposes only the narrow surfaces needed by
host applications:
AgentEngine.Agent— load agent config and instruction entriesAgentEngine.Session— functional session state containerAgentEngine.PhaseGates— phased system cue generationAgentEngine.BudgetHints— budget-awareness cue generationAgentEngine.TrendHints— response-quality trend cue generationAgentEngine.Collaboration— shared state for multi-agent work