release v1.4.0 - `LaunchSettings.append_system_prompt_files` -- array of file paths that are concatenated (newline-separated) before delivery to the tool. Enables base + overlay prompt composition for harness shared instructions (e.g. a shared `HARNESS-base.md` stacked with a per-harness `HARNESS.md` overlay). For `prompt_mode = "string"` (Pi) the composition is inlined into `--append-system-prompt`; for `prompt_mode = "file"` (Claude Code) it is materialised into a single temp file and passed via `--append-system-prompt-file`. Backward- compatible: the singular `append_system_prompt_file` still works; the array takes precedence when both are set (with a logged warning).