Usage of non standard JSON schema

[amirh]

Splitting off #293

• why are you not using standard JSON schema? this json schema-like but not quite json schema because the type fields are uppercased enums makes zero sense to me and is really bad for interop with other tools. json schema is a standard for a reason – please consider using it. if you have to support only a subset of it, that's fine, but slightly changing the spec is really annoying imho.
• both typing and execution-wise, if I'm using AI tools and JSON schema definitions generated from other places, this won't "just work". it'll require a weird transformation step.
• same for not supporting the additionalProperties attribute
• i'm not able to, for instance, use the stdlib of tools from https://github.com/transitive-bullshit/agentic without
• example of me trying unsuccessfully to get this to work: https://github.com/transitive-bullshit/google-ai-test/blob/main/src/function-calling-1.ts