refactor(agent-loop): simplify observable state machine

examples/headless-agent/tests/fixtures/goal-domain/seed-goal.ts

@@ -7,7 +7,7 @@ export const name = 'seed-goal'
 export const inject = ['goals']
 
 export function apply(ctx: Context): void {
-  ctx.on('agent/pre-step', (agent) => {
+  ctx.on('agent/step', (agent) => {
     if (ctx.goals.get(agent) !== undefined) return
     ctx.goals.create(agent, {
       objective: 'Prove the composed goal survives in the session log',