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

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+# OpenSpec Change: enterprise-font-compress-btf
+
+- **Change ID**: enterprise-font-compress-btf
+- **Package**: `@suaveplan/font-compress`
+- **Category**: universal
+- **Target path**: `universal/compression/font-compress`
+- **Status**: PROPOSED
+- **Date**: 2026-04-25
+- **Reference source**: `/mnt/s/web/suaveplan/packages/universal/font-compress/src/packer/`
+
+---
+
+## Summary
+
+Deliver `@suaveplan/font-compress` on the genesis branch from scratch at enterprise quality. The package implements BTF (Binary TypeFace) binary packing: takes a `TypefaceFont` JSON (from `@suaveplan/font-convert`) and produces a compact `Uint8Array` using dictionary-based compression with `@suaveplan/bitpacker`. Also provides `BinaryFontUnpacker` which reverses the process (BTF binary → `TypefaceFont` JSON).
+
+---
+
+## Current-state audit (genesis)
+
+The package does not exist on genesis. The original logic was split across `@suaveplan/font-compress` (packing) and `@suaveplan/font-decompress` (unpacking) on main. In genesis we co-locate packer and unpacker here since they share the binary format and dictionary logic.
+
+---
+
+## BTF binary format
+
+```
+[metadata: familyName string][cssFontWeight string][cssFontStyle string]
+[reversed: 1 byte]
+[dictLen: uint32][dictionary: Int16Array × dictLen]
+[metrics: 9 × uint16 (indexes into dictionary)]
+[glyphCount: uint32]
+[per glyph: char codepoint uint32][ha/x_min/x_max: 3 × uint16][cmdCount: uint16]
+[per cmd: type byte + coord indexes uint16 × 2|4|0]
+```
+
+String encoding: `[length: uint16][utf8 bytes]`
+
+---
+
+## Available workspace deps on genesis
+
+| Package | Role |
+|---|---|
+| `@suaveplan/error` (`workspace:^`) | Base class for `FontCompressError`; `FONT_COMPRESS.*` codes |
+| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock` |
+| `@suaveplan/font-convert` (`workspace:^`) | `TypefaceFont`, `TypefaceGlyph`, `PathCommand` types |
+| `@suaveplan/bitpacker` (`workspace:^`) | `BitWriter`/`BitReader` for bit-packed command encoding |
+| `zod` (`catalog:forms`) | Option schemas |
+| `@opentelemetry/api` (`catalog:observability`) | Spans + metrics |
+
+---
+
+## Public API
+
+```ts
+class FontCompressError extends SuaveplanError<FontCompressErrorCode>
+
+type FontCompressErrorCode =
+  | 'FONT_COMPRESS_PACK_FAILED'
+  | 'FONT_COMPRESS_UNPACK_FAILED'
+  | 'FONT_COMPRESS_INVALID_DATA'
+
+class BinaryFontPacker {
+    pack(font: TypefaceFont): Uint8Array
+}
+
+class BinaryFontUnpacker {
+    unpack(data: Uint8Array): TypefaceFont
+}
+
+function createBinaryFontPacker(): BinaryFontPacker
+function createBinaryFontUnpacker(): BinaryFontUnpacker
+```
+
+---
+
+## File layout
+
+```text
+universal/compression/font-compress/
+  package.json
+  tsconfig.lib.json
+  vitest.config.ts
+  vite.config.ts
+  src/
+    index.ts
+    error-codes.ts
+    constants/
+      index.ts
+    packer/
+      binary-font-packer/
+        binary-font-packer.ts
+        binary-font-packer.md
+        binary-font-packer.test.ts
+        index.ts
+    unpacker/
+      binary-font-unpacker/
+        binary-font-unpacker.ts
+        binary-font-unpacker.md
+        binary-font-unpacker.test.ts
+        index.ts
+    utils/
+      encode-string.ts
+      encode-string.md
+      encode-string.test.ts
+      parse-path.ts
+      parse-path.md
+      parse-path.test.ts
+    __benchmarks__/
+      font-compress.bench.ts
+  tests/
+    roundtrip.test.ts
+    property.test.ts
+```
+
+---
+
+## Impact
+
+**Downstream**: Three.js font loading pipelines.
+**Prerequisites**: `@suaveplan/font-convert`, `@suaveplan/bitpacker`.