SUPERTONIC_CACHE_DIR ignored when model name is passed (the default code path)

[dominvo]

Summary

SUPERTONIC_CACHE_DIR is documented as the way to override the model cache location, but it is silently ignored on the most common code path — when TTS() is constructed with a model name (which is the default behaviour, since model: str = 'supertonic-3' in the TTS.__init__ signature).

Reproduction (supertonic 1.2.3)

export SUPERTONIC_CACHE_DIR=/tmp/custom-cache
python3 -c "
from supertonic import TTS
tts = TTS(auto_download=True)
print('model_dir:', tts.model_dir)
"

Expected: model_dir: /tmp/custom-cache
Actual: model_dir: /Users/<user>/.cache/supertonic3

The env var is fully honored only if model_name=None is passed explicitly, which contradicts both the docstring of get_cache_dir() and the comment in config.py:24 that suggests the env var is the user-facing override.

Root cause

supertonic/loader.py:58-60:

if model_name is not None:
    cache_dir = get_model_cache_dir(model_name)   # ← hardcoded ~/.cache/{name}
else:
    cache_dir = Path(DEFAULT_CACHE_DIR)            # ← env-var aware

get_model_cache_dir() in config.py:77-87 is hardcoded to Path.home() / ".cache" / config["cache_dir"] regardless of SUPERTONIC_CACHE_DIR.

Suggested fix

One-liner — make get_model_cache_dir honor the env var, e.g.:

def get_model_cache_dir(model_name: str) -> Path:
    config = get_model_config(model_name)
    base = os.environ.get("SUPERTONIC_CACHE_DIR")
    if base:
        return Path(base)
    return Path.home() / ".cache" / config["cache_dir"]

(Or, equivalently, make get_cache_dir() consult DEFAULT_CACHE_DIR first and fall back to get_model_cache_dir() only when the env var is unset.)

Workaround for now

Pass model_dir explicitly:

import os
from supertonic import TTS
tts = TTS(auto_download=True, model_dir=os.environ.get("SUPERTONIC_CACHE_DIR"))

Not a blocker — just a friction point for anyone redirecting caches to a non-default volume (external SSDs, network mounts, container volumes). Thanks for the great library!