Add translation and TTS caching

tests/test_tts_retry.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import asyncio
 
+from src import engines
 from src.engines import Engine
 from src.translation import TranslationConfig
 
@@ -46,3 +47,39 @@ def test_synthesize_retries_transient_edge_tts_failure(tmp_path, monkeypatch):
     assert calls["count"] == 2
     assert out_path.exists()
     assert out_path.stat().st_size == 2048
+
+
+def test_synthesize_uses_tts_cache(tmp_path, monkeypatch):
+    calls = {"count": 0}
+    cache_dir = tmp_path / "tts-cache"
+    monkeypatch.setattr(engines, "TTS_CACHE_DIR", cache_dir)
+
+    class FakeCommunicate:
+        def __init__(self, text, voice, rate):
+            self.text = text
+            self.voice = voice
+            self.rate = rate
+
+        async def save(self, out_path):
+            calls["count"] += 1
+            with open(out_path, "wb") as audio_file:
+                audio_file.write(b"1" * 2048)
+
+    monkeypatch.setattr("src.engines.edge_tts.Communicate", FakeCommunicate)
+
+    engine = Engine(
+        "cpu",
+        translation_config=TranslationConfig(
+            base_url="http://127.0.0.1:1234/v1",
+            api_key="test-key",
+            model="test-model",
+        ),
+    )
+    first_out = tmp_path / "first.mp3"
+    second_out = tmp_path / "second.mp3"
+
+    asyncio.run(engine.synthesize("Bonjour", "fr", first_out))
+    asyncio.run(engine.synthesize("Bonjour", "fr", second_out))
+
+    assert calls["count"] == 1
+    assert first_out.read_bytes() == second_out.read_bytes()