Gemma 4 not registered in LLMRegistry — `Gemma.supported_models()` only matches `gemma-3.*`

[epicwhale]

Using model="gemma-4-31b-it" (string) in an ADK Agent raises:

ValueError: Model gemma-4-31b-it not found.

Gemma.supported_models() returns [r'gemma-3.*'], so the registry never
routes Gemma 4 model strings to the Gemma class.

Workaround: Using Gemini(model="gemma-4-31b-it") as the model value
bypasses the registry and works correctly — including tool calling with
thinking parts. This confirms the underlying API support is fine; only the
registry pattern is missing.

Suggested fix: Update the regex in Gemma.supported_models() to
r'gemma-.*' (or add r'gemma-4.*').

Versions: google-adk 1.28.1, Python 3.14

Steps to reproduce:

1. pip install google-adk>=1.28.1
2. Set GOOGLE_API_KEY env var
3. Run this file: python gemma4_bug_repro.py

import asyncio

from dotenv import load_dotenv

load_dotenv(".env")

from google.adk.agents import Agent
from google.adk.models.google_llm import Gemini
from google.adk.models.gemma_llm import Gemma
from google.adk.models.registry import LLMRegistry
from google.adk.runners import Runner
from google.adk.sessions import InMemorySessionService
from google.genai import types
import datetime


def get_current_time() -> dict:
    """Returns the current date and time."""
    now = datetime.datetime.now()
    return {
        "date": now.strftime("%Y-%m-%d"),
        "time": now.strftime("%H:%M:%S"),
    }


# ---------------------------------------------------------------------------
# BUG: Registry does not recognize gemma-4-* as a string
# ---------------------------------------------------------------------------
def demo_registry_miss():
    print("=" * 70)
    print("BUG: model='gemma-4-31b-it' (string) — not found in registry")
    print("=" * 70)
    LLMRegistry.resolve.cache_clear()
    try:
        LLMRegistry.resolve("gemma-4-31b-it")
        print("PASS — model resolved (unexpected on ADK 1.28.1)\n")
    except ValueError as e:
        print(f"FAIL — {e}\n")


# ---------------------------------------------------------------------------
# WORKAROUND: Gemini(model=...) bypasses the registry and works fine
# ---------------------------------------------------------------------------
async def demo_gemini_workaround():
    print("=" * 70)
    print("WORKAROUND: model=Gemini(model='gemma-4-31b-it') — works")
    print("=" * 70)

    agent = Agent(
        model=Gemini(model="gemma-4-31b-it"),
        name="test_agent",
        description="A test agent.",
        instruction="Use get_current_time when the user asks for the time.",
        tools=[get_current_time],
    )

    svc = InMemorySessionService()
    await svc.create_session(app_name="repro", user_id="u1", session_id="s1")
    runner = Runner(agent=agent, app_name="repro", session_service=svc)

    msg = types.Content(
        role="user",
        parts=[types.Part.from_text(text="What is the current time?")],
    )

    tool_was_called = False
    final_text = ""

    async for event in runner.run_async(
        user_id="u1", session_id="s1", new_message=msg
    ):
        if event.content and event.content.parts:
            for part in event.content.parts:
                if part.function_call:
                    tool_was_called = True
                    print(f"  tool_call: {part.function_call.name}({part.function_call.args})")
                if part.function_response:
                    print(f"  tool_response: {part.function_response.response}")
                if part.text and not getattr(part, "thought", False):
                    final_text = part.text

    if tool_was_called:
        print(f"  PASS — tool called, response: {final_text!r}\n")
    else:
        print(f"  FAIL — tool was NOT called, response: {final_text!r}\n")


# ---------------------------------------------------------------------------
# Run
# ---------------------------------------------------------------------------
if __name__ == "__main__":
    demo_registry_miss()
    asyncio.run(demo_gemini_workaround())