[Bug] When Gemini model, agent will only return string response even when response_model is set.

[DataSolveProblems]

When using Gemini models, agent is unable to convert the output into the correct structured output type. For example, from the agent run below, the expected output should be a NewsArticle object, but string output is returned instead. This only happens to Gemini models.

Code to reproduce the issue

from typing import Optional
from pydantic import BaseModel, Field
from agno.agent import Agent
from agno.models.google import Gemini
from agno.tools.duckduckgo import DuckDuckGoTools

class NewsArticle(BaseModel):
    title: str = Field(..., description="Title of the article.")
    url: str = Field(..., description="Link to the article.")
    summary: Optional[str] = Field(..., description="Summary of the article if available.")

class SearchResults(BaseModel):
    articles: list[NewsArticle]

agent = Agent(
    # model=Gemini(id='gemini-2.0-flash'),
    model=Gemini(id='gemini-2.0-flash-lite-preview-02-05'),
    tools=[DuckDuckGoTools()],
    instructions=['Given a topic, search for the top 5 articles.'],
    add_datetime_to_instructions=True, # add the current date
    response_model=SearchResults,
    structured_outputs=True,
    debug_mode=True,
    show_tool_calls=True,
)

response = agent.run('Search for today\'s top news')

Log

DEBUG    *********** Agent Run End:
         20d98dba-126b-4129-ada8-7cec33cf246b ***********
WARNING  Failed to convert response to response_model