[#407] Agents: Avoid calling tools that haven't been explicitly enabled

[aidando73]

What does this PR do?

Contributes to issue (#407)

tl;dr - @subramen was getting a 500 error because llama-stack called code_interpreter when it never was defined as a tool.

Prevents failures like:

# Server side
Traceback (most recent call last):
  File "/opt/conda/envs/llamastack-vllm-stack/lib/python3.10/site-packages/llama_stack/distribution/server/server.py", line 206, in sse_generator
    async for item in await event_gen:
  File "/opt/conda/envs/llamastack-vllm-stack/lib/python3.10/site-packages/llama_stack/providers/impls/meta_reference/agents/agents.py", line 138, in _create_agent_turn_streaming
    async for event in agent.create_and_execute_turn(request):
  File "/opt/conda/envs/llamastack-vllm-stack/lib/python3.10/site-packages/llama_stack/providers/impls/meta_reference/agents/agent_instance.py", line 179, in create_and_execute_turn
    async for chunk in self.run(
  File "/opt/conda/envs/llamastack-vllm-stack/lib/python3.10/site-packages/llama_stack/providers/impls/meta_reference/agents/agent_instance.py", line 252, in run
    async for res in self._run(
  File "/opt/conda/envs/llamastack-vllm-stack/lib/python3.10/site-packages/llama_stack/providers/impls/meta_reference/agents/agent_instance.py", line 560, in _run
    result_messages = await execute_tool_call_maybe(
  File "/opt/conda/envs/llamastack-vllm-stack/lib/python3.10/site-packages/llama_stack/providers/impls/meta_reference/agents/agent_instance.py", line 824, in execute_tool_call_maybe
    assert name in tools_dict, f"Tool {name} not found"
AssertionError: Tool code_interpreter not found

Instead, if the model hallucinates, we just let it hallucinate and let the client know.

Test Plan

pytest llama_stack/providers/tests/agents/test_agents.py -k ollama

llama stack build --template ollama --image-type conda 
conda activate llamastack-ollama

llama_stack/providers/tests/agents/test_agents.py ..Fss                                                                                          [100%]

======================================================================= FAILURES =======================================================================
_________________________________________ TestAgents.test_rag_agent_as_attachments[--ollama][ollama] __________________________________________
llama_stack/providers/tests/agents/test_agents.py:261: in test_rag_agent_as_attachments
    turn_response = [
llama_stack/providers/tests/agents/test_agents.py:261: in <listcomp>
    turn_response = [
llama_stack/providers/inline/agents/meta_reference/agents.py:153: in _create_agent_turn_streaming
    async for event in agent.create_and_execute_turn(request):
llama_stack/providers/inline/agents/meta_reference/agent_instance.py:179: in create_and_execute_turn
    async for chunk in self.run(
llama_stack/providers/inline/agents/meta_reference/agent_instance.py:250: in run
    async for res in self._run(
llama_stack/providers/inline/agents/meta_reference/agent_instance.py:363: in _run
    rag_context, bank_ids = await self._retrieve_context(
llama_stack/providers/inline/agents/meta_reference/agent_instance.py:698: in _retrieve_context
    bank_id = await self._ensure_memory_bank(session_id)
llama_stack/providers/inline/agents/meta_reference/agent_instance.py:653: in _ensure_memory_bank
    await self.memory_banks_api.register_memory_bank(
llama_stack/providers/utils/telemetry/trace_protocol.py:101: in async_wrapper
    result = await method(self, *args, **kwargs)
llama_stack/distribution/routers/routing_tables.py:312: in register_memory_bank
    raise ValueError(
E   ValueError: Embeddings are now served via Inference providers. Please upgrade your run.yaml to include inline::sentence-transformer as an additional inference provider. See https://github.com/meta-llama/llama-stack/blob/main/llama_stack/templates/together/run.yaml for an example.
=============================================================== short test summary info ================================================================
FAILED llama_stack/providers/tests/agents/test_agents.py::TestAgents::test_rag_agent_as_attachments[--ollama] - ValueError: Embeddings are now served via Inference providers. Please upgrade your run.yaml to include inline::sentence-transformer as an additiona...
========================================== 1 failed, 2 passed, 2 skipped, 20 deselected, 5 warnings in 14.24s ==========================================

Unrelated test is failing (also failing on main)

Manual

Using this client code: https://github.com/aidando73/llama-stack-apps/blob/7ebc257b27bb120fe13e11d9d668a467a33e137d/client.py

Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [x] Ran pre-commit to handle lint / formatting issues.
• [x] Read the contributor guideline, Pull Request section?
• [ ] Updated relevant documentation.
• [ ] Wrote necessary unit or integration tests.