# ACMS Strategy Coordinator & Fusion Engine

## Overview

The **StrategyCoordinator** and **FusionEngine** are named facades that
provide clean public APIs over the existing ACMS pipeline Phase 1 and
Phase 2 components respectively.

## Architecture

```
┌──────────────────────────────────────────────────────────┐
│                  StrategyCoordinator                     │
│  ┌──────────────────┐ ┌──────────────────┐ ┌──────────┐  │
│  │ Confidence       │ │ Proportional     │ │ Parallel │  │
│  │ Weighted         │ │ Budget           │ │ Strategy │  │
│  │ Selector         │ │ Allocator        │ │ Executor │  │
│  └────────┬─────────┘ └────────┬─────────┘ └────┬─────┘  │
│           │ select             │ allocate       │execute │
│           └────────────────────┴────────────────┘        │
│                         coordinate()                     │
└─────────────────────────┬────────────────────────────────┘
                          │ fragments
                          ▼
┌────────────────────────────────────────────────────────┐
│                     FusionEngine                       │
│  ┌──────────┐ ┌───────────┐ ┌─────────┐ ┌───────────┐  │
│  │ Content  │ │ Max Depth │ │Weighted │ │ Greedy    │  │
│  │ Hash     │ │ Resolver  │ │Composite│ │ Knapsack  │  │
│  │ Dedup    │ │           │ │ Scorer  │ │ Packer    │  │
│  └────┬─────┘ └─────┬─────┘ └────┬────┘ └─────┬─────┘  │
│       │ dedup       │ resolve    │ score      │ pack   │
│       └─────────────┴────────────┴────────────┘        │
│                          fuse()                        │
│  ┌──────────────────────────────────────────────────┐  │
│  │            Budget Overage Guard                  │  │
│  │  Drop lowest-relevance fragments if over budget  │  ││  └──────────────────────────────────────────────────┘  │
└────────────────────────────────────────────────────────┘
```

## StrategyCoordinator

### Public API

```python
coordinator = StrategyCoordinator(config=CoordinatorConfig(
    per_strategy_max_cap=500,
    min_useful_budget=64,
))

result = coordinator.coordinate(
    request={"preferred_strategies": ["relevance"]},
    strategies=[strategy_a, strategy_b],
    budget=ContextBudget(max_tokens=4096),
    fragments=input_fragments,
    backends={"vector": True},
    plan_context={"plan_id": "..."},
)

# Result: CoordinationResult
#   .fragments: list[ContextFragment]
#   .strategies_used: list[str]
#   .allocations: list[tuple[str, float, int]]
#   .circuit_broken: list[str]
```

### Budget Allocation

Budget tokens are allocated **proportionally by strategy confidence**:

- Strategy with confidence 0.8 in a pool of (0.8 + 0.2) = 1.0
  receives 80% of the budget.
- The largest-remainder method ensures no tokens are lost to rounding.
- Strategies whose proportional share falls below `min_useful_budget`
  are excluded and their tokens are redistributed.

### Per-Strategy Max Caps

When `per_strategy_max_cap` is set:

1. Any allocation exceeding the cap is clamped.
2. Excess tokens are redistributed proportionally among uncapped
   strategies.
3. Redistributed tokens are also capped to prevent cascading overflows.

### Error Handling

- **Circuit breaker**: After `circuit_breaker_threshold` consecutive
  failures, a strategy is temporarily disabled. Disabled strategies
  appear in `result.circuit_broken`.
- **Timeouts**: Per-strategy execution timeout of `executor_timeout`
  seconds. Timed-out strategies are treated as failures.
- **Graceful degradation**: Failed strategies are excluded from results
  without failing the entire coordination round.

## FusionEngine

### Public API

```python
engine = FusionEngine(config=FusionConfig(
    overage_guard_enabled=True,
    min_fragment_tokens=10,
))

result = engine.fuse(
    fragments=coordinator_output.fragments,
    budget=ContextBudget(max_tokens=4096),
)

# Result: FusionResult
#   .fragments: list[ContextFragment]
#   .dedup_count: int
#   .depth_resolved_count: int
#   .dropped_by_overage_guard: int
#   .total_tokens: int
#   .budget_utilization: float
```

### Fragment Dedup

Fragments are grouped by **(UKO URI, SHA-256 hash of content)**.
Within each group, the fragment with the highest `relevance_score`
is retained.

### Detail Conflict Resolution

When the same UKO node appears at multiple detail depths:
- The highest-depth rendering is retained.
- Equal depths: prefer higher `relevance_score`.

### Greedy Knapsack Packing

Fragments are sorted with **deterministic tie-breakers**:

1. `relevance_score` descending
2. `detail_depth` descending
3. `token_count` ascending

The greedy algorithm fills the budget top-down. When a high-value
fragment doesn't fit, **depth fallback** attempts lower-depth
renderings of the same UKO node.

### Budget Overage Guard

A post-packing safety net that:

1. Checks if total tokens exceed the available budget.
2. Drops fragments in ascending order of `relevance_score`.
3. Emits structured `WARNING` log messages for each dropped fragment.
4. Continues until total tokens fit within budget.

## Configuration Reference

### CoordinatorConfig

| Field | Type | Default | Description |
|---|---|---|---|
| `min_useful_budget` | `int` | 64 | Min tokens per strategy |
| `executor_timeout` | `float` | 30.0 | Per-strategy timeout (seconds) |
| `executor_max_workers` | `int` | 4 | Max concurrent threads |
| `circuit_breaker_threshold` | `int` | 3 | Failures before circuit opens |
| `preference_boost` | `float` | 1.5 | Confidence multiplier for preferred |
| `per_strategy_max_cap` | `int \| None` | None | Max tokens per strategy |

### FusionConfig

| Field | Type | Default | Description |
|---|---|---|---|
| `scorer_weights` | `ScorerWeights \| None` | None | Composite scoring weights |
| `depth_fallback_steps` | `tuple[int, ...]` | (9,4,2,0) | Depth fallback sequence |
| `min_fragment_tokens` | `int` | 10 | Min tokens for packing |
| `overage_guard_enabled` | `bool` | True | Enable budget overage guard |