Default Context / Context Resolver

[mbleigh]

When building a complex project that has non-trivial context, it's difficult to make it work with the Dev UI for a few reasons:

1. Dev UI does not currently support context well throughout (e.g. tools)
2. Even if it did, context is not always representable as JSON

I have a couple ideas to address this:

const ai = genkit({...});
// 1. Have a "default context" that is settable after genkit init
ai.applyContext({foo: 'bar'}); // now context will always be `{foo: 'bar'}` unless explicitly passed
ai.applyContext((actionMeta, input, {context}) => { /* set programmatically */ });
ai.defineTool({..., defaultContext: {...}}); // alternative
// 2. Have a "context resolver" that can translate JSON from Dev UI to context
ai.defineTool({..., resolveContext: (inputContext) => outputContext)});

Needs more noodling, but wanted to record.