Tasks — i18n number and relative-time formatters

Every checkbox MUST reflect work actually done in this change. Do not retroactively tick.

Audit Note (2026-05-02)

Minimal progress — DEFERRED, do not archive.

packages/i18n/i18n/src/formatting/ only contains currency and date. No number/ or relative-time/ directories.
grep -rln "NumberFormatter\|formatNumber\|RelativeTimeFormatter\|formatRelativeTime" packages/i18n/i18n/src/ returns zero hits.
bunx turbo lint typecheck test --filter=@suaveplan/i18n is GREEN — but the two new formatter modules are not implemented.
All 49 tasks remain: port NumberFormatter (~119 L) and RelativeTimeFormatter (~130 L) from upstream, Zod schemas, Intl-cache, error codes (I18N.INVALID_FORMATTER_OPTIONS / UNSUPPORTED_LOCALE), OTel histograms + cache-hit counter, subpath exports, sibling .mds, README links.

1.1 Read ../suaveplan/enterprise/i18n.md end-to-end
1.2 Read openspec/specs/i18n/spec.md (canonical capability spec)
1.3 Read openspec/AGENTS.md Sections 13 and 14
1.4 Draft proposal.md from openspec/templates/proposal.md
1.5 Fill ## Source mapping table — cite upstream number.ts / relative-time.ts line ranges
1.6 Draft specs/i18n/spec.md from openspec/templates/spec-delta.md
1.7 Every requirement carries a **Verified by:** line naming concrete it(...) titles
1.8 openspec change validate i18n-formatters exits with no errors

2.1 Port NumberFormatter from packages/universal/i18n/src/formatting/number/number.ts (L1-L119) into packages/i18n/i18n/src/formatting/number/number.ts
2.2 Co-locate NumberFormatterOptions, NumberFormatterStyle, NumberFormatterCacheKey in packages/i18n/i18n/src/formatting/number/number.types.ts
2.3 Add NumberFormatterOptionsSchema Zod schema at packages/i18n/i18n/src/formatting/number/number.schema.ts
2.4 Implement (locale, options-hash) cache for Intl.NumberFormat; expose clearCache() for tests
2.5 Throw I18nError with I18N.INVALID_FORMATTER_OPTIONS on Zod failure; I18N.UNSUPPORTED_LOCALE on RangeError from Intl.NumberFormat constructor
2.6 Export formatNumber(value, locale, options?) standalone helper

3.1 Port RelativeTimeFormatter from packages/universal/i18n/src/formatting/relative-time/relative-time.ts (L1-L130) into packages/i18n/i18n/src/formatting/relative-time/relative-time.ts
3.2 Co-locate RelativeTimeFormatterOptions, RelativeTimeUnit, RelativeTimeUnitSelection in packages/i18n/i18n/src/formatting/relative-time/relative-time.types.ts
3.3 Add RelativeTimeFormatterOptionsSchema Zod schema
3.4 Port unit threshold table (seconds → minutes → hours → days → weeks → months → years) verbatim from L40-L96
3.5 Implement (locale, options-hash) cache for Intl.RelativeTimeFormat
3.6 Export formatRelativeTime(deltaMs, locale, options?) standalone helper

4.1 Add I18N.INVALID_FORMATTER_OPTIONS, I18N.UNSUPPORTED_LOCALE to packages/i18n/i18n/src/errors/error-codes.ts via defineCodes
4.2 Emit OTel histograms i18n.format.number.duration_ms and i18n.format.relative_time.duration_ms from production paths
4.3 Emit OTel counter i18n.format.cache_hit (tagged by formatter type) on cache reuse

5.1 Update packages/i18n/i18n/src/formatting/index.ts to re-export NumberFormatter, formatNumber, RelativeTimeFormatter, formatRelativeTime and their types
5.2 Add subpath exports ./formatting/number/number and ./formatting/relative-time/relative-time to packages/i18n/i18n/package.json exports
5.3 Update root README.md ## Modules section to link the two new co-located .mds

6.1 packages/i18n/i18n/src/formatting/number/number.test.ts — decimal, percent, currency styles round-trip; fraction-digit clamping; useGrouping toggle; notation modes (standard/compact/scientific/engineering)
6.2 packages/i18n/i18n/src/formatting/number/number.spec-conformance.test.ts — Zod rejects unknown style → INVALID_FORMATTER_OPTIONS; bogus locale → UNSUPPORTED_LOCALE; cache hit increments OTel counter
6.3 packages/i18n/i18n/src/formatting/relative-time/relative-time.test.ts — auto-unit selection across boundaries (60s → 1m, 60m → 1h, etc.); negative deltas; style and numeric overrides
6.4 packages/i18n/i18n/src/formatting/relative-time/relative-time.spec-conformance.test.ts — Zod rejects unknown style; histogram records duration_ms; expectTypeOf<RelativeTimeUnit> matches the literal union
6.5 Every it(...) carries { timeout: 5000 }

7.1 Sibling .md for number.ts (≥200 words, basic + advanced examples, full API reference)
7.2 Sibling .md for relative-time.ts (≥200 words, basic + advanced examples)
7.3 README links both new .mds under ## Modules

8.1 bun run check — Biome 0/0/0 across the monorepo
8.2 bunx turbo lint typecheck test --filter=@suaveplan/i18n — green
8.3 bunx turbo test:coverage --filter=@suaveplan/i18n — 100/100/100/100
8.4 bun scripts/openspec-conformance.ts @suaveplan/i18n — exit 0, no error findings
8.5 bunx turbo build --filter=@suaveplan/i18n — green

9.1 Generics threaded; expectTypeOf assertions on NumberFormatterStyle and RelativeTimeUnit literal unions
9.2 Zod schemas wired at every public boundary (NumberFormatterOptionsSchema, RelativeTimeFormatterOptionsSchema)
9.3 Both new error codes thrown from at least one production path
9.4 Strict-mode tested: bogus locale fallback vs throw paths
9.5 OTel histograms / counters emitted from production paths and asserted with a real in-memory MeterProvider
9.6 Lifecycle dedup: cache reuse verified; clearCache() empties the map
9.7 No retroactive tick — every box reflects work done in this change

10.1 Fold spec delta into openspec/specs/i18n/spec.md
10.2 Move openspec/changes/i18n-formatters/ → openspec/archive/<yyyy-mm-dd>-i18n-formatters/
10.3 Refresh MANIFEST.md if package set or deps changed