chore: backoff als tuple, exception-chain via raise-from

app/ingest/embedder.py

@@ -10,7 +10,7 @@ from app.config import get_settings
 logger = logging.getLogger(__name__)
 
 
-_BACKOFF_SECONDS = [1, 2, 4]
+_BACKOFF_SECONDS: tuple[int, ...] = (1, 2, 4)
 
 
 class EmbeddingError(Exception):
@@ -47,7 +47,7 @@ async def _embed_one(text: str, model: str) -> list[float]:
                     extra={"event": "embed_retry", "attempt": attempt + 1, "wait_s": wait, "error": str(exc)},
                 )
                 await asyncio.sleep(wait)
-    raise EmbeddingError(f"embed failed after retries: {last_err}")
+    raise EmbeddingError("embed failed after retries") from last_err
 
 
 async def embedding_dimension(model: str) -> int: