# OpenSpec Change: enterprise-network-failover

- **Change ID**: enterprise-network-failover
- **Package**: `@suaveplan/network-failover`
- **Category**: universal/network
- **Target path**: `universal/network/network-failover`
- **Status**: SUPERSEDED-BY-GENESIS-WAVE
- **Date**: 2026-04-24
- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/network-failover.md`

---

## Summary

Deliver `@suaveplan/network-failover` on the genesis branch from scratch at enterprise quality. The package provides network failover and recovery: health-checked connection groups, automatic failover on primary failure, configurable failover strategies (round-robin, fastest, weighted), recovery detection and fail-back, and in-flight request replay after failover. Genesis adds structured errors via `@suaveplan/error`, Zod schemas for all failover configuration, OTel instrumentation on failover events, `AbortSignal` on recovery operations, injectable `Clock` for health-check intervals, event-bus integration for failover state changes, and property-based tests for strategy correctness.

---

## Current-state audit (genesis)

The package does not exist on genesis yet — this is a fresh build.

---

## Available workspace deps on genesis

| Package | Role |
|---|---|
| `@suaveplan/error` (`workspace:^`) | Base class for `NetworkFailoverError`; stable error codes |
| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock`, `EventBusLike` |
| `@suaveplan/events` (`workspace:^`) | Event bus for failover events |
| `@suaveplan/logger` (`workspace:^`) | Structured logging |
| `@suaveplan/retry` (`workspace:^`) | Retry wired into health checks and recovery probes |
| `@suaveplan/timing` (`workspace:^`) | Interval timer for health checks |
| `zod` (`catalog:forms`) | Zod schemas |
| `@opentelemetry/api` (`catalog:observability`) | Spans + counters on failover |
| `tslib` (`catalog:build`) | Runtime helpers |

Dev deps: `vitest`, `@vitest/coverage-istanbul`, `fast-check` (all `catalog:testing`).

---

## Public API surface

### Core

```ts
function createFailoverGroup(options: FailoverGroupOptions): FailoverGroup

interface FailoverGroup {
  readonly primary: FailoverTarget | null
  readonly targets: ReadonlyArray<FailoverTarget>
  readonly state: FailoverState
  addTarget(target: FailoverTarget): void
  removeTarget(targetId: string): void
  execute<T>(fn: (target: FailoverTarget, signal?: AbortSignal) => Promise<T>, signal?: AbortSignal): Promise<T>
  probe(targetId: string, signal?: AbortSignal): Promise<HealthStatus>
  on(event: FailoverEvent, handler: (data: FailoverEventData) => void): () => void
}
```

### Target types

```ts
interface FailoverTarget {
  id: string
  address: string
  port?: number
  weight?: number
  priority?: number
  tags?: string[]
  healthCheck?: HealthCheckConfig
}

interface HealthCheckConfig {
  intervalMs?: number
  timeoutMs?: number
  successThreshold?: number
  failureThreshold?: number
  probe?: (target: FailoverTarget, signal?: AbortSignal) => Promise<boolean>
}

type HealthStatus = {
  healthy: boolean
  latencyMs?: number
  checkedAt: number
  consecutiveFailures: number
  consecutiveSuccesses: number
}
```

### Failover types

```ts
type FailoverState = 'healthy' | 'failing-over' | 'degraded' | 'recovering' | 'no-targets'
type FailoverStrategy = 'round-robin' | 'fastest' | 'weighted' | 'priority'
type FailoverEvent = 'failover' | 'recovery' | 'target-failed' | 'target-recovered' | 'state-change'

interface FailoverEventData {
  previousPrimary?: FailoverTarget
  newPrimary?: FailoverTarget
  target?: FailoverTarget
  reason?: string
}

interface FailoverGroupOptions {
  strategy?: FailoverStrategy
  failoverDelayMs?: number
  failBackDelayMs?: number
  maxRetries?: number
  logger?: LoggerLike
  clock?: Clock
  eventBus?: EventBusLike
}
```

### Error codes

```ts
type NetworkFailoverErrorCode =
  | 'FAILOVER_NO_TARGETS'
  | 'FAILOVER_ALL_UNHEALTHY'
  | 'FAILOVER_EXECUTE_FAILED'
  | 'FAILOVER_PROBE_FAILED'
  | 'FAILOVER_ABORT'

function registerNetworkFailoverErrorCodes(): void
```

---

## Genesis additions

1. **Structured `NetworkFailoverError`** with stable `FAILOVER.*` codes
2. **Zod schemas** for `FailoverGroupOptions`, `FailoverTarget`, `HealthCheckConfig`
3. **Four failover strategies**: round-robin, fastest (lowest latency), weighted, priority
4. **Automatic health checking** via injectable interval timer and `@suaveplan/timing`
5. **Fail-back with delay** — prevents oscillation; configurable `failBackDelayMs`
6. **In-flight request retry** on failover — `execute()` replays on new primary with `AbortSignal`
7. **Injectable `Clock`** for health-check interval testing
8. **OTel instrumentation** — span `failover.execute`, counter `failover.events_total`, histogram `failover.latency_ms`
9. **Property-based tests** — failover always selects a healthy target when available; strategy returns consistent ordering

---

## File layout

```text
universal/network/network-failover/
  package.json
  tsconfig.json
  vitest.config.ts
  src/
    index.ts
    error-codes.ts
    constants/
      index.ts
    types/
      common.ts
      common.md
    core/
      failover-group/
        failover-group.ts
        failover-group.md
        failover-group.types.ts
        failover-group.test.ts
        index.ts
      health-checker/
        health-checker.ts
        health-checker.md
        health-checker.test.ts
        index.ts
    strategies/
      round-robin.ts
      round-robin.md
      round-robin.test.ts
      fastest.ts
      fastest.md
      fastest.test.ts
      weighted.ts
      weighted.md
      weighted.test.ts
      priority.ts
      priority.md
      priority.test.ts
  tests/
    integration.test.ts
    property.test.ts
```

---

## Impact

**Workspace dep prerequisites**: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/events`, `@suaveplan/logger`, `@suaveplan/retry`, `@suaveplan/timing` must be published.