# @suaveplan/i18n-backend-storage - Universal translation backend backed by any AbstractStorage from @suaveplan/storage. Three wire layouts: single-key-per-namespace (default), single-key-per-locale, flat-keys. Pluggable codec, AbortSignal cancellation, OpenTelemetry instrumentation under i18n.backend.storage.*. Zero runtime dependencies on @suaveplan/i18n core.

## Summary

Universal translation backend for the `@suaveplan/i18n` family,
backed by any `AbstractStorage` implementation from
`@suaveplan/storage`. Implements the full `Backend` contract
(`read`, `readMulti`, `save`, `lastModified`) over three wire
layouts: `single-key-per-namespace` (default),
`single-key-per-locale`, and `flat-keys`. Pluggable codec, optional
`AbortSignal` cancellation, OpenTelemetry instrumentation under the
`i18n.backend.storage.*` prefix. Zero runtime dependencies on
`@suaveplan/i18n` core.

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## Documentation tree

- [backend](./src/backend/backend.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
  - [backend](./src/backend/backend.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
  - [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
  - [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
<!-- end:auto-docs -->  - [backend](./src/backend/backend.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_- [backend](./src/backend/backend.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_- [backend](./src/backend/backend.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_- [backend](./src/backend/backend.md) — <!-- begin:auto-docs --> _(no submodules)_- [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_  - [factory](./src/factory/factory.md) — <!-- begin:auto-docs --> _(no submodules)_- [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_  - [observability](./src/observability/observability.md) — <!-- begin:auto-docs --> _(no submodules)_
## Why this exists

The Wave 5 modular split lifts each backend out of the
`@suaveplan/i18n` monolith into its own sibling so consumers can
install only the backends they need. The storage backend is the
canonical persistence layer: pair it with `MemoryStorage` for tests,
`OpfsStorage` / `IndexedDBStorage` for offline-first browser apps,
or `S3Storage` / `GarageStorage` / `NodeFsStorage` /
`SqliteStorage` for server-tier deployments. Splitting it out also
isolates `@suaveplan/storage` as a transitive dep — consumers using
only the HTTP or memory backends no longer pull it in.

## Install

```bash
bun add @suaveplan/i18n-backend-storage @suaveplan/storage
```

## Quick Start

```ts
import { storageBackend } from "@suaveplan/i18n-backend-storage";
import { MemoryStorage } from "@suaveplan/storage";

const backend = storageBackend({ storage: new MemoryStorage() });

await backend.save("en", "auth", { login: { title: "Sign in" } });
const record = await backend.read("en", "auth");
// → { login: { title: "Sign in" } }
```

## Modules

| Subpath | Description |
|---|---|
| `@suaveplan/i18n-backend-storage` | Root barrel — class + factory + types + schemas + observability |
| `@suaveplan/i18n-backend-storage/backend` | `StorageBackend` class + `defaultCodec` |
| `@suaveplan/i18n-backend-storage/factory` | `storageBackend` factory function only |
| `@suaveplan/i18n-backend-storage/schemas` | Zod boundary schemas |
| `@suaveplan/i18n-backend-storage/observability` | OTel instruments + in-memory state ring |

## Modules Documentation

- [backend.md](src/backend/backend.md) — `StorageBackend` class, layouts, codec
- [factory.md](src/factory/factory.md) — `storageBackend` factory function
- [observability.md](src/observability/observability.md) — OTel instruments + cardinality

## Capabilities

| Flag | Value | Notes |
|---|---|---|
| `canRead` | `true` | always |
| `canReadMulti` | `true` | per-layout dispatch |
| `canSave` | `true` | persists into the wrapped storage |
| `canTrackModification` | `true` | consults `getMetadata().modifiedAt` |
| `canWatch` | `false` | the storage contract has no change feed |

## Layouts

- `single-key-per-namespace` (default) — one key per `(locale, ns)`
  at `<prefix>/<locale>/<namespace>.json`. Best for HTTP-CDN-style
  storages.
- `single-key-per-locale` — one key per locale holding the whole
  namespace map. Best when namespaces are small and read together.
- `flat-keys` — one key per leaf string at
  `<prefix>:<locale>:<namespace>:<dotPath>`. Best for content-
  addressed storages with cheap per-leaf delta shipping.

## Testing

The package's own tests use the shared `runBackendConformance`
harness from `@suaveplan/i18n-shared/testing` so the universal
`Backend` contract is exercised against a fresh storage backend
per assertion (against all three layouts):

```ts
import { runBackendConformance } from "@suaveplan/i18n-shared/testing";
import { StorageBackend } from "@suaveplan/i18n-backend-storage";
import { MemoryStorage } from "@suaveplan/storage";

runBackendConformance("StorageBackend", async () => {
    const backend = new StorageBackend({ storage: new MemoryStorage() });
    return {
        backend,
        async seed(locale, namespace, record) {
            await backend.save(locale, namespace, record as never);
        },
    };
});
```

## Versioning

This package is part of the i18n modular-split rollout. Stays at
`0.1.0` until the slim core (Wave 6) cuts the family `1.0.0`
release. The metric names under `i18n.backend.storage.*` are part of
the public API contract and will not change without a major bump.

## Wave 5 Scope

This package is Wave 5b of the 14-package i18n modular split. It
ships pure additions only — `packages/i18n/i18n/src/core/backend/storage/`
retains its copy of the backend until Wave 6 deletes it. Both
copies coexist during Wave 5; downstream consumers continue to
import from the monolith and observe no behaviour change.