fix(embedding): harden API error handling (PR #1671 review)

Address the gemini-code-assist review on #1671:

- Wrap `http.client.HTTPException` (BadStatusLine / IncompleteRead — common
  with local/overloaded servers) and `ValueError` (invalid/missing URL scheme;
  also subsumes `json.JSONDecodeError`) in `EmbeddingAPIError` instead of
  letting them crash the caller.
- Reject a non-dict top-level JSON response before calling `.get()` on it, so a
  JSON list/`null`/string yields a clear `EmbeddingAPIError` rather than an
  unhandled `AttributeError`.
- Add tests for all three cases.

mempalace/embedding.py

@@ -526,6 +526,7 @@ class OpenAICompatEmbeddingFunction:
         return self(input)
 
     def __call__(self, input):  # noqa: A002 — ChromaDB EF protocol uses `input`
+        import http.client
         import json
         from urllib.error import HTTPError, URLError
         from urllib.request import Request, urlopen
@@ -550,7 +551,10 @@ class OpenAICompatEmbeddingFunction:
             try:
                 with urlopen(req, timeout=_EF_API_TIMEOUT) as resp:
                     data = json.loads(resp.read())
-            except (HTTPError, URLError, OSError, json.JSONDecodeError) as e:
+            # ValueError covers an invalid/missing URL scheme and json.JSONDecodeError;
+            # http.client.HTTPException covers low-level protocol faults (BadStatusLine,
+            # IncompleteRead) common with local/overloaded servers.
+            except (HTTPError, URLError, OSError, http.client.HTTPException, ValueError) as e:
                 raise EmbeddingAPIError(
                     f"Embedding API request to {self._url} failed: {e}. Check that the "
                     f"server is reachable and MEMPALACE_EMBEDDING_API_URL / embedding_api_url "
@@ -572,6 +576,10 @@ class OpenAICompatEmbeddingFunction:
         """
         import numpy as np
 
+        if not isinstance(data, dict):
+            raise EmbeddingAPIError(
+                f"Embedding API at {self._url} returned a non-object response: {data}"
+            )
         rows = data.get("data")
         if not isinstance(rows, list):
             raise EmbeddingAPIError(

tests/test_embedding_api.py

@@ -285,6 +285,40 @@ def test_raises_on_non_contiguous_indices(monkeypatch):
         ef(["a", "b"])
 
 
+def test_raises_on_http_protocol_exception(monkeypatch):
+    # BadStatusLine / IncompleteRead — common with local/overloaded servers.
+    from http.client import HTTPException
+
+    def boom(req, timeout=None):
+        raise HTTPException("incomplete read")
+
+    monkeypatch.setattr("urllib.request.urlopen", boom)
+    ef = embedding.OpenAICompatEmbeddingFunction("http://h", "m")
+    with pytest.raises(embedding.EmbeddingAPIError, match="failed"):
+        ef(["a"])
+
+
+def test_raises_on_value_error_from_urlopen(monkeypatch):
+    # urlopen raises ValueError on an invalid/missing URL scheme.
+    def boom(req, timeout=None):
+        raise ValueError("unknown url type")
+
+    monkeypatch.setattr("urllib.request.urlopen", boom)
+    ef = embedding.OpenAICompatEmbeddingFunction("http://h", "m")
+    with pytest.raises(embedding.EmbeddingAPIError, match="failed"):
+        ef(["a"])
+
+
+def test_raises_on_non_object_response(monkeypatch):
+    def bad(req, timeout=None):
+        return _FakeResp(json.dumps([1, 2, 3]).encode())  # JSON list, not an object
+
+    monkeypatch.setattr("urllib.request.urlopen", bad)
+    ef = embedding.OpenAICompatEmbeddingFunction("http://h", "m")
+    with pytest.raises(embedding.EmbeddingAPIError, match="non-object response"):
+        ef(["a"])
+
+
 def test_raises_and_surfaces_server_error_body(monkeypatch):
     # HTTP 200 with an OpenAI-style error envelope (no "data") — surface it.
     def err(req, timeout=None):