# OpenSpec Change: i18n-spec-conformance-followup

- **Change ID**: i18n-spec-conformance-followup
- **Package**: `@suaveplan/i18n`
- **Status**: PROPOSED
- **Date**: 2026-05-04
- **Reference**: `openspec/changes/archive/2026-05-04-i18n-spec-conformance/`

## Why

Three items were intentionally scoped out of `i18n-spec-conformance` because each requires a dedicated migration sweep. They are tracked here so the `@suaveplan/i18n` spec contract and runtime stay aligned.

## Summary

- Wire engine-constructor option validation through `.parse()` so `I18nError(I18N.INVALID_OPTIONS)` carries `context.zodIssues` directly instead of through the hand-written mirror checks.
- Narrow `MessageCatalog.t` / `.get` to `K extends DotPaths<TMessages> | (string & {})` and migrate every in-repo consumer signature.
- Move `tests/property.test.ts` into `tests/properties/` and split `src/__benchmarks__/i18n.bench.ts` into `catalog.bench.ts` / `interpolation.bench.ts` / `pluralization.bench.ts` per `I18N-13` / `I18N-14`.

## Impact

- `@suaveplan/i18n` runtime constructors throw the same error class but with a richer `context.zodIssues` payload.
- Consumers that imported `t(key: string)` will see TypeScript flag unknown keys when `TMessages` is supplied; the `(string & {})` escape hatch keeps existing string call-sites compiling.
- No public API removed; no change to dep graph.