Additional instructions appended to Pi Coding Agent's system prompt.
The value is either:
- Inline content as a string
- A path to a file containing the content
The configured content is written to APPEND_SYSTEM.md inside programs.pi-coding-agent.configDir (default ~/.pi/agent/APPEND_SYSTEM.md).
A project-local .pi/APPEND_SYSTEM.md takes precedence over this file.