# Phase 4: Feedback Loop

**Purpose:** The core primitive — plan → execute → observe → reflect → refine.
**TS Module:** `src/tier2-primitives/loops/feedback-loop.ts`

## What It Does

Runs the phase machine for N iterations until convergence:

```
plan → execute → observe → reflect → refine
  ↑                                      │
  └──────────────────────────────────────┘
```

Each phase produces structured output stored in the state accumulator.

## PhaseExecutor Interface

Implement this to connect any model:

```typescript
interface PhaseExecutor {
  plan(task: string, previousIteration: LoopIteration | null): Promise<string>;
  execute(plan: string): Promise<string>;
  observe(executed: string): Promise<string>;
  reflect(observation: string, previousIteration: LoopIteration | null): Promise<string>;
  refine(reflection: string): Promise<string>;
}
```

## Usage

```bash
fable-agent run "Your goal" --loop 10
```

## Key Rules

- The executor determines the model — swap it to route phases differently
- Hooks: `onPhase`, `onIteration`, `onConverge` for observability
- The loop converges via rubric criteria, not iteration count