Guard chunk_and_stitch_embed against a non-positive cap

The shared helper assumed cap was positive; a cap <= 0 (a caller
misconfiguration) surfaced as a raw range() error (0) or a misleading
empty-stitch validation failure (< 0). Raise ValueError eagerly with a
clear message, mirroring the chunk_size guard TeiEmbeddingProvider
already applies at construction.

Author: chris-colinsky

src/openarmature/retrieval/_wire.py

@@ -117,6 +117,11 @@ async def chunk_and_stitch_embed(
     per-mapping wire shaping, POST, and parse live in the closure. Returns the
     stitched :class:`EmbeddingResponse`.
     """
+    # cap is the provider's per-call input limit; a non-positive cap is a caller
+    # misconfiguration -- fail loudly rather than surfacing a raw range() error
+    # (cap == 0) or a misleading empty-stitched validation failure (cap < 0).
+    if cap <= 0:
+        raise ValueError(f"cap must be positive (got {cap})")
     stitched_vectors: list[list[float]] = []
     chunk_bodies: list[Any] = []
     input_tokens_total: int | None = None

tests/unit/test_retrieval_provider.py

@@ -1492,6 +1492,19 @@ def handler(req: httpx.Request) -> httpx.Response:
     assert response.response_id is None
 
 
+async def test_chunk_and_stitch_embed_rejects_non_positive_cap() -> None:
+    # The shared helper guards a caller passing cap <= 0 (a misconfigured per-call
+    # limit): fail loudly rather than a raw range() error (0) or an empty stitch.
+    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, []
+
+    for bad_cap in (0, -1):
+        with pytest.raises(ValueError, match="cap must be positive"):
+            await chunk_and_stitch_embed(["a"], model="m", cap=bad_cap, embed_chunk=_noop)
+
+
 # --- /rerank wire + chunk-and-stitch ----------------------------------------