Gemma 4 12B: incompatible with opencode, or just awful at tool calling?

Yesterday I tried out Gemma 4 12B on a significant coding challenge, to compare it to prior results with Qwen models. I ran the 8-bit quant, so I'm not dumbing it down much at all.

Judging from the partial results, it seemed capable of grasping the task, but it burned far too much time and effort trying to successfully do basic tool calls. Over and over it would fail to specify "pattern" successfully to a "grep" tool, for instance, and the call would be rejected. Ultimately I interrupted it because it didn't feel like this was going to be productive.

Is opencode lacking in compatibility with Gemma 4 12B, or the other way around? Is there a harness with which people are seeing reliable tool calls from Gemma 4 12B?

Thanks!