QVAC-18417: multilingual (MeCab/Cangjie) preprocessing wiring for tts-ggml Chatterbox

[freddy311082]

Summary

Wires the multilingual text-preprocessing dictionaries through the tts-ggml
Chatterbox addon so the multilingual (MTL) GGUF can correctly synthesize
languages that need word-level segmentation — primarily Japanese (ja) via
MeCab/IPAdic, plus the Cangjie TSV slot for Chinese (zh).

The actual MeCab/Cangjie segmentation already lives in tts-cpp
(EngineOptions::mecab_dict_path / cangjie_tsv_path); this PR only forwards
the host-resolved dictionary paths from JS down to the native layer. No
preprocessing logic is duplicated in the addon. Dictionaries are staged by the
host (and, for tests, downloaded from the QVAC model registry / S3) rather than
bundled.

Changes

Addon (C++)

• ChatterboxConfig.hpp: add mecabDictPath + cangjieTsvPath fields.
• JSAdapter.cpp: read both from the JS config object.
• ChatterboxModel.cpp: map them into tts_cpp::chatterbox::EngineOptions
  only when non-empty (empty ⇒ tts-cpp keeps its character-level fallback, so
  Turbo English is unaffected).

JS

• index.js: accept mecabDictDir / mecabDictPath / cangjieTsvPath
  (top-level or via files.*) and pass them into the Chatterbox params.
• index.d.ts: document the new options.

Tests / infra

• test/utils/downloadModel.js: ensureMecabDict() helper that stages the
  6 compiled IPAdic files (char.bin, dicrc, matrix.bin, mecabrc,
  sys.dic, unk.dic) from the registry (S3 prefix
  qvac_models_compiled/chatterbox/mecab-ipadic/) and returns the dir.
• test/integration/chatterbox-ja-mecab.test.js: Japanese (kanji + kana)
  synthesis smoke test that downloads the dict, passes it via
  files.mecabDictDir, and asserts audio is produced. Skip-as-pass when the
  MTL GGUFs or the dictionary are unavailable (offline / no registry access).

Dependencies

• Bumps tts-cpp to >= 2026-05-29 (the multilingual version that introduces
  mecab_dict_path / cangjie_tsv_path; this corresponds to ext-lib
  whisper.cpp PR updated qvac-cli readme #19 / commit d3db516d).

[kinsta]

Preview deployments for qvac-docs-staging ⚡️

Status	Branch preview	Commit preview
✅ Ready	Visit preview	Visit preview

Commit: e3dd8e272c758f163637c424e1492508b25f6ebb

Deployment ID: 3f10cfbc-efb4-4730-9f5a-d1bdae17a492

Static site name: qvac-docs-staging-fazwv

[github-actions]

Tier-based Approval Status

**PR Tier:** TIER1

**Current Status:** ✅ APPROVED

**Requirements:**
- 1 Team Member approval ✅ (1/1)
- 1 Team Lead OR Management approval ✅ (1/1)



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*This comment is automatically updated when reviews change.*

[freddy311082]

CI ran here: https://github.com/tetherto/qvac/actions/runs/26965296773

[freddy311082]

/review