fix(vector): nested-group drop classification + review/Sonar fixes (#893)

Round-1 review on PR #893:
- _drop_reason now descends through nested ExceptionGroups to the first leaf
  (was single-level), so a doubly-wrapped cause isn't mislabelled "other";
  added a nested-group test. Commented why both the httpx and openai isinstance
  branches exist (raw Nextcloud-API errors vs SDK-wrapped variants).
- Documented that generate() intentionally shares the broadened transient retry
  (RAG sampling path), with the worst-case latency note.
- Added a docstring note to process_document on how the provider-level retry
  (5x) layers over the outer loop (3x in-process / 1x procrastinate).
- Added test_embed_batch_retries_on_connection_error for the batch path.
- Renamed test_retry_reraises_non_rate_limit_immediately ->
  test_retry_reraises_when_predicate_returns_false (it tests the predicate, not
  a specific status).

SonarCloud:
- S5708 (BLOCKER) on the helper's dynamic `except exception_type`: the type is
  constrained to BaseException/tuple by the signature; suppressed with a
  justified NOSONAR.
- S7503 (async without await) in the embed-retry test: use AsyncMock side_effect
  instead of a hand-rolled async function.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/providers/test_openai.py

@@ -396,19 +396,41 @@ async def test_embed_retries_on_connection_error(mock_openai_client, monkeypatch
     mock_response = MagicMock()
     mock_response.data = [mock_embedding_data]
 
-    calls = {"n": 0}
-
-    async def _flaky(*args, **kwargs):
-        calls["n"] += 1
-        if calls["n"] == 1:
-            raise APIConnectionError(request=_req())
-        return mock_response
-
-    mock_openai_client.embeddings.create = _flaky
+    # First call raises a transient connection error, second succeeds.
+    create = AsyncMock(side_effect=[APIConnectionError(request=_req()), mock_response])
+    mock_openai_client.embeddings.create = create
     provider = OpenAIProvider(
         api_key="test-key", embedding_model="text-embedding-3-small"
     )
 
     result = await provider.embed("hello")
     assert result == [0.1, 0.2, 0.3]
-    assert calls["n"] == 2  # one failure, one success
+    assert create.await_count == 2  # one failure, one success
+
+
+@pytest.mark.unit
+async def test_embed_batch_retries_on_connection_error(mock_openai_client, monkeypatch):
+    """The batch path (`_embed_batch_request`) shares the transient retry too."""
+    from openai import APIConnectionError
+
+    from nextcloud_mcp_server.providers import _retry
+
+    monkeypatch.setattr(_retry.anyio, "sleep", AsyncMock(return_value=None))
+
+    data = MagicMock()
+    data.embedding = [0.4, 0.5, 0.6]
+    data.index = 0
+    mock_response = MagicMock()
+    mock_response.data = [data]
+    mock_response.usage.total_tokens = 7
+
+    create = AsyncMock(side_effect=[APIConnectionError(request=_req()), mock_response])
+    mock_openai_client.embeddings.create = create
+    provider = OpenAIProvider(
+        api_key="test-key", embedding_model="text-embedding-3-small"
+    )
+
+    embeddings, tokens = await provider.embed_batch_with_usage(["text"])
+    assert embeddings == [[0.4, 0.5, 0.6]]
+    assert tokens == 7
+    assert create.await_count == 2

tests/unit/providers/test_retry.py

@@ -39,8 +39,8 @@ async def test_retry_succeeds_after_429():
 
 
 @pytest.mark.unit
-async def test_retry_reraises_non_rate_limit_immediately():
-    """A non-rate-limit error of the same class is re-raised on first hit."""
+async def test_retry_reraises_when_predicate_returns_false():
+    """An error the predicate rejects is re-raised on first hit (no retry)."""
     calls = {"n": 0}
 
     @_retry.retry_on_transient(_FakeError, should_retry=lambda e: e.status_code == 429)

tests/unit/test_processor_drop_reason.py

@@ -59,6 +59,15 @@ def test_exception_group_unwraps_to_leaf():
     assert processor._drop_reason(group) == "connection"
 
 
+@pytest.mark.unit
+def test_nested_exception_group_descends_to_leaf():
+    """A doubly-wrapped group must still classify by its leaf, not 'other'."""
+    nested = BaseExceptionGroup(
+        "outer", [BaseExceptionGroup("inner", [httpx.ReadTimeout("slow")])]
+    )
+    assert processor._drop_reason(nested) == "timeout"
+
+
 @pytest.mark.unit
 def test_qdrant_namespace_classified():
     from qdrant_client.http.exceptions import UnexpectedResponse