fix: remove global add_function_to_prompt — breaks native tool calling (Groq, OpenAI)

[vitas]

Problem

_ensure_litellm_imported() sets litellm.add_function_to_prompt = True globally at import time (line 188). This forces ALL models through LiteLLM's text-based tool calling path — tool definitions are injected into the system prompt as text instead of being passed as the tools parameter.

Models that support native function calling (Groq, OpenAI, Anthropic) then output XML-style function tags instead of proper tool_calls JSON:

<function=run_command {"command": "kubectl get pods -n demo"} </function>

Groq rejects with:

{"error":{"message":"Failed to call a function. See 'failed_generation'","code":"tool_use_failed"}}

Proof

Direct litellm.completion() inside the same environment without the global flag returns proper tool_calls JSON with finish_reason: "tool_calls":

# Works (direct LiteLLM, no global flag):
litellm.completion(model="groq/llama-3.3-70b-versatile", tools=[...])
# → finish_reason: "tool_calls", proper JSON ✓

# Fails (via ADK, which sets the global flag):
Agent(model=LiteLlm(model="groq/llama-3.3-70b-versatile"), tools=[...])
# → XML tags, Groq 400 ✗

Fix

Remove the global litellm.add_function_to_prompt = True. Models that need text-based tool calling (e.g., some Ollama models without native support) can opt in per-instance:

LiteLlm(model="ollama/qwen2", add_function_to_prompt=True)

This kwarg flows through _additional_args into acompletion(), so per-model opt-in already works.

Impact

• Fixes: All models with native tool calling (Groq, OpenAI, Anthropic) through LiteLlm
• No regression for models without native tool calling: They can pass add_function_to_prompt=True explicitly
• One line removed, comment added explaining why

References

• [BUG] Groq API fails to call tools for ToolCallingAgents huggingface/smolagents#1119 — same XML tag issue across frameworks
• Groq not working well with the Litellm definition of tools. BerriAI/litellm#11001 — Groq tool calling format issues
• Introduced in f33e090 for Support tool-calling for LLMs with coding skills #1273 (support models without native tool calling)

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[adk-bot]

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