Enable references and progress messages from chat variable resolvers

[roblourens]

Today when you register a IPromptContextResolver for a variable and it returns references, those references do not show up in the Used references:

@workspace where they are used:

#codebase where they are not used:

does it matter what references the variable uses? Maybe it matters more so what the intent actually used?

Or maybe not… maybe it’s better to enumerate everything that was pulled in?

[roblourens]

I think we should pass a limited version of a ChatAgentResponseStream to the variable resolver, which will allow it to send references and progress updates.

And also, if the agent uses that variable, maybe it should have to pass the variable name as a reference, and only in that case will the variable's references appear.

[roblourens]

Here we can give the variable resolver a limited stream:

export interface ChatVariableResolverResponseStream {

	/**
	 * Push a progress part to this stream. Short-hand for
	 * `push(new ChatResponseProgressPart(value))`.
	 *
	 * @param value
	 * @returns This stream.
	 */
	progress(value: string): ChatAgentResponseStream;

	/**
	 * Push a reference to this stream. Short-hand for
	 * `push(new ChatResponseReferencePart(value))`.
	 *
	 * *Note* that the reference is not rendered inline with the response.
	 *
	 * @param value A uri or location
	 * @returns This stream.
	 */
	reference(value: Uri | Location): ChatAgentResponseStream;
}

export interface ChatVariableResolver {
	/**
	 * A callback to resolve the value of a chat variable.
	 * @param name The name of the variable.
	 * @param context Contextual information about this chat request.
	 * @param token A cancellation token.
	 */
	resolve(name: string, context: ChatVariableContext, stream: ChatVariableResolverResponseStream, token: CancellationToken): ProviderResult<ChatVariableValue[]>;
}

And here the agent can report a used reference for the variable, then I imagine #codebase rendered in the list with those references nested beneath it.

export class ChatVariableReference {
	variableName: string;
	constructor(variableName: string);
}

...

export interface ChatAgentResponseStream {
    reference(value: Uri | Location | ChatVariableReference): ChatAgentResponseStream;
}

[andreamah]

Not sure if this is enough to verify, but saw progress messages and references for #codebase