Validate input in chunk_and_stitch_embed

An empty input reaching the shared helper fell through to
validate_embedding_response and raised provider_invalid_response
("provider returned no vectors"), misclassifying a caller-side invalid
request as an invalid response. Call validate_embedding_input up front so
an empty (or non-string) input raises provider_invalid_request. Providers
already validate before the helper; this protects a direct/future caller.

Author: chris-colinsky

src/openarmature/retrieval/_wire.py

@@ -15,7 +15,7 @@
 
 from openarmature.llm.errors import ProviderInvalidResponse
 
-from .provider import validate_embedding_response
+from .provider import validate_embedding_input, validate_embedding_response
 from .response import EmbeddingResponse, EmbeddingUsage
 
 
@@ -122,6 +122,12 @@ async def chunk_and_stitch_embed(
     # (cap == 0) or a misleading empty-stitched validation failure (cap < 0).
     if cap <= 0:
         raise ValueError(f"cap must be positive (got {cap})")
+    # Validate the input up front (empty / non-string) so an empty input raises
+    # provider_invalid_request -- the caller-side contract error -- rather than
+    # falling through to a misclassified provider_invalid_response from the
+    # empty stitched-count check. Providers already call this before the helper;
+    # this protects a direct / future caller.
+    validate_embedding_input(input_strings)
     stitched_vectors: list[list[float]] = []
     chunk_bodies: list[Any] = []
     input_tokens_total: int | None = None

tests/unit/test_retrieval_provider.py

@@ -1505,6 +1505,18 @@ async def _noop(chunk: list[str]) -> tuple[list[list[float]], None, None, list[A
             await chunk_and_stitch_embed(["a"], model="m", cap=bad_cap, embed_chunk=_noop)
 
 
+async def test_chunk_and_stitch_embed_rejects_empty_input() -> None:
+    # An empty input reaching the helper is a caller error -> provider_invalid_request
+    # (validate_embedding_input), NOT a misclassified provider_invalid_response.
+    from openarmature.retrieval._wire import chunk_and_stitch_embed
+
+    async def _noop(chunk: list[str]) -> tuple[list[list[float]], None, None, list[Any]]:
+        return [], None, None, []
+
+    with pytest.raises(ProviderInvalidRequest):
+        await chunk_and_stitch_embed([], model="m", cap=4, embed_chunk=_noop)
+
+
 # --- /rerank wire + chunk-and-stitch ----------------------------------------