[Agent] main agent is very persistent about entering plan mode when creating hello world app

[gundermanc]

Repro:

1. Ask Gemini CLI to create a hello world node js app.
2. It then prompts you to enter plan mode.
3. Cancel and repeat 2-3 times.

It alternates between being very persistent about entering plan mode and/or just proceeding to ask you the next step in your plan, as if it has entered plan mode.

I suspect we have some prompt that is too firmly telling the agent it "MUST" enter plan mode when creating a new project and we're not giving it an out when the user rejects it.

I propose:

• Adding a behavioral eval that checks 2-3 different "scopes" of project to enter plan mode for. IMO hello world app probably doesn't require it.
• Adding a behavioral eval that checks that the user can reject entering plan mode and then run the same prompt again without getting prompted to enter plan mode again.