fix: Agent-level knowledge sources with non-OpenAI embedders

- Remove OpenAI default from KnowledgeStorage
- Add proper embedder config inheritance from crew to agent
- Improve error messaging for missing embedder config
- Add tests for agent-level knowledge sources

Fixes #2164

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/test_agent_knowledge.py

@@ -0,0 +1,94 @@
+import pytest
+from unittest.mock import patch, MagicMock
+
+from chromadb.api.types import EmbeddingFunction
+from crewai import Agent, Crew, Task
+from crewai.knowledge.source.string_knowledge_source import StringKnowledgeSource
+from crewai.process import Process
+
+class MockEmbeddingFunction(EmbeddingFunction):
+    def __call__(self, texts):
+        return [[0.0] * 1536 for _ in texts]
+
+@pytest.fixture(autouse=True)
+def mock_vector_db():
+    """Mock vector database operations."""
+    with patch("crewai.knowledge.storage.knowledge_storage.KnowledgeStorage") as mock, \
+         patch("chromadb.PersistentClient") as mock_chroma:
+        # Mock ChromaDB client and collection
+        mock_collection = MagicMock()
+        mock_collection.query.return_value = {
+            "ids": [["1"]],
+            "distances": [[0.1]],
+            "metadatas": [[{"source": "test"}]],
+            "documents": [["Test content"]]
+        }
+        mock_chroma.return_value.get_or_create_collection.return_value = mock_collection
+        
+        # Mock the query method to return a predefined response
+        instance = mock.return_value
+        instance.query.return_value = [
+            {
+                "context": "Test content",
+                "score": 0.9,
+            }
+        ]
+        instance.reset.return_value = None
+        yield instance
+
+def test_agent_knowledge_with_custom_embedder(mock_vector_db):
+    agent = Agent(
+        role="test role",
+        goal="test goal",
+        backstory="test backstory",
+        knowledge_sources=[StringKnowledgeSource(content="test content")],
+        embedder_config={
+            "provider": "custom",
+            "config": {
+                "embedder": MockEmbeddingFunction()
+            }
+        }
+    )
+    assert agent.knowledge is not None
+    assert agent.knowledge.storage.embedder is not None
+
+def test_agent_inherits_crew_embedder(mock_vector_db):
+    test_agent = Agent(
+        role="test role",
+        goal="test goal",
+        backstory="test backstory"
+    )
+    test_task = Task(
+        description="test task",
+        expected_output="test output",
+        agent=test_agent
+    )
+    crew = Crew(
+        agents=[test_agent],
+        tasks=[test_task],
+        process=Process.sequential,
+        embedder_config={
+            "provider": "custom",
+            "config": {
+                "embedder": MockEmbeddingFunction()
+            }
+        }
+    )
+    agent = Agent(
+        role="test role",
+        goal="test goal",
+        backstory="test backstory",
+        knowledge_sources=[StringKnowledgeSource(content="test content")],
+        crew=crew
+    )
+    assert agent.knowledge is not None
+    assert agent.knowledge.storage.embedder is not None
+
+def test_agent_knowledge_without_embedder_raises_error(mock_vector_db):
+    with pytest.raises(ValueError, match="No embedder configuration provided"):
+        agent = Agent(
+            role="test role",
+            goal="test goal",
+            backstory="test backstory",
+            knowledge_sources=[StringKnowledgeSource(content="test content")]
+        )