Merge Agent System Prompt with Project System Prompt when Both are Set

Currently, only one system prompt can be active at a time — either an Agent System Prompt or a Project System Prompt.

It would be great to support merging these. For example, I have a project-level system prompt that instructs the model to access certain information via MCP as base context. I'd like to use this project prompt in combination with different agent prompts simultaneously (e.g., Business Consultant, Technical Consultant, etc.).