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openspec/archive/2026-04-25-enterprise-font-subset/proposal.md

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+# OpenSpec Change: enterprise-font-subset
+
+- **Change ID**: enterprise-font-subset
+- **Package**: `@suaveplan/font-subset`
+- **Category**: universal
+- **Target path**: `universal/compression/font-subset`
+- **Status**: PROPOSED
+- **Date**: 2026-04-24
+- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/font-compress.md`
+
+---
+
+## Summary
+
+Deliver `@suaveplan/font-subset` on the genesis branch from scratch at enterprise quality. The package provides font subsetting and compression: Unicode range subsetting (remove glyphs not in a given character set), WOFF2 encoding, WOFF encoding, TTF-to-OTF normalisation, feature tag filtering (OpenType layout features), hinting strip, and metadata strip. Pure TypeScript; binary font operations delegate to an injectable `FontCompressAdapter`.
+
+---
+
+## Current-state audit (genesis)
+
+The package does not exist on genesis yet — this is a fresh build. No prior source, no test results, no coverage data. The main-branch package had 95%+ coverage.
+
+---
+
+## Available workspace deps on genesis
+
+| Package | Role |
+|---|---|
+| `@suaveplan/error` (`workspace:^`) | Base class for `FontCompressError`; `FONT_COMPRESS.*` codes |
+| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock` |
+| `@suaveplan/mime` (`workspace:^`) | Font MIME-type detection |
+| `zod` (`catalog:forms`) | Zod schemas for all public option types |
+| `@opentelemetry/api` (`catalog:observability`) | Spans + counters |
+
+Dev deps: `vitest`, `@vitest/coverage-istanbul`, `fast-check`, `mitata` (all `catalog:testing`).
+
+---
+
+## Public API
+
+### Core types
+
+```ts
+class FontCompressError extends SuaveplanError
+
+type FontFormat = 'ttf' | 'otf' | 'woff' | 'woff2' | 'unknown'
+
+interface FontMetadata {
+  format: FontFormat
+  mimeType: string
+  byteSize: number
+  glyphCount?: number
+  familyName?: string
+  subFamilyName?: string
+  version?: string
+}
+
+interface SubsetOptions {
+  unicodeRanges?: string[]    // e.g. ['U+0020-007F', 'U+00A0-00FF']
+  characters?: string         // literal character string to include
+  glyphIds?: number[]         // explicit glyph IDs to include
+}
+
+interface CompressFontOptions {
+  subset?: SubsetOptions
+  outputFormat?: FontFormat   // default: 'woff2'
+  stripHinting?: boolean      // default: true
+  stripMetadata?: boolean     // default: false
+  features?: string[]         // OpenType feature tags to retain; empty = all
+}
+
+interface FontCompressResult {
+  data: Uint8Array
+  format: FontFormat
+  mimeType: string
+  originalSize: number
+  compressedSize: number
+  ratio: number
+  glyphCount?: number
+}
+
+interface FontCompressAdapter {
+  readonly supportedInputFormats: readonly FontFormat[]
+  readonly supportedOutputFormats: readonly FontFormat[]
+  probe(data: Uint8Array): Promise<FontMetadata>
+  compress(data: Uint8Array, options: CompressFontOptions): Promise<FontCompressResult>
+}
+
+interface FontCompressorOptions {
+  adapter: FontCompressAdapter
+  logger?: LoggerLike
+  clock?: Clock
+}
+
+class FontCompressor {
+  constructor(options: FontCompressorOptions)
+  probe(data: Uint8Array): Promise<FontMetadata>
+  compress(data: Uint8Array, options?: CompressFontOptions, signal?: AbortSignal): Promise<FontCompressResult>
+}
+
+function createFontCompressor(options: FontCompressorOptions): FontCompressor
+```
+
+### Error codes
+
+```ts
+type FontCompressErrorCode =
+  | 'FONT_COMPRESS_UNSUPPORTED_FORMAT'
+  | 'FONT_COMPRESS_PARSE_FAILED'
+  | 'FONT_COMPRESS_ENCODE_FAILED'
+  | 'FONT_COMPRESS_INVALID_OPTIONS'
+  | 'FONT_COMPRESS_SUBSET_FAILED'
+
+const FONT_COMPRESS_ERROR_METADATA: Readonly<Record<FontCompressErrorCode, CodeMetadata>>
+function registerFontCompressErrorCodes(): void
+```
+
+### Zod schemas
+
+```ts
+SubsetOptionsSchema
+CompressFontOptionsSchema
+FontMetadataSchema
+FontCompressResultSchema
+FontCompressorOptionsSchema
+```
+
+---
+
+## New additions for genesis
+
+1. **`FontCompressAdapter` interface** — codec-agnostic; `NullFontCompressAdapter` ships for unit tests.
+2. **Unicode range parser** — `parseUnicodeRanges(ranges: string[]): Set<number>` utility; parses `U+XXXX` and `U+XXXX-XXXX` notation into a codepoint set.
+3. **Format detection** — delegates to `@suaveplan/mime` for initial sniff of TTF/OTF/WOFF/WOFF2 magic bytes.
+4. **`AbortSignal` propagation** — passed to adapter; throws `FontCompressError(FONT_COMPRESS_ENCODE_FAILED)` on abort.
+5. **OTel instrumentation** — span `font.compress`, counter `font_compress_total`, histogram `font_compress_duration_ms` + `font_compress_ratio`.
+6. **Property-based tests** — compressed size ≤ original size for any valid options, ratio in (0, 1].
+7. **Benchmark suite** — probe 200 kB TTF, WOFF2 encode 200 kB TTF, subset to ASCII range.
+
+---
+
+## File layout
+
+```text
+universal/compression/font-subset/
+  package.json
+  tsconfig.json
+  vitest.config.ts
+  src/
+    index.ts
+    error-codes.ts
+    constants/
+      index.ts
+    types/
+      common.ts
+      common.md
+    core/
+      font-compressor/
+        font-compressor.ts
+        font-compressor.md
+        font-compressor.types.ts
+        font-compressor.test.ts
+        index.ts
+    adapters/
+      null-adapter/
+        null-adapter.ts
+        null-adapter.md
+        null-adapter.test.ts
+        index.ts
+    utils/
+      unicode-ranges.ts
+      unicode-ranges.md
+      unicode-ranges.test.ts
+      format-detect.ts
+      format-detect.md
+      format-detect.test.ts
+    __benchmarks__/
+      font-compress.bench.ts
+  tests/
+    integration.test.ts
+    property.test.ts
+```
+
+---
+
+## Impact
+
+**Downstream**: font-loading pipelines, `@suaveplan/font-decompress`.
+**Breaking changes**: none — fresh build.
+**Prerequisites**: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/mime` published to Verdaccio.