Creates a system prompt given the execution context and input.

This is a functional interface extending BiFunction for Java interoperability. The context provides access to the blackboard, process options, and other execution state. The input is the string passed to the agentic tool.

Example usage in Kotlin:

tool.withSystemPrompt { ctx, input ->
    "You are helping user ${ctx.processContext.processOptions.contextId}. Task: $input"
}

Example usage in Java:

tool.withSystemPrompt((ctx, input) ->
    "You are helping user " + ctx.getProcessContext().getProcessOptions().getContextId()
);