MASH (Multi-Agent Software Harness) is a structured development framework for Claude Code that manages the full software lifecycle — from idea to tested, committed code. It orchestrates four specialized AI personas (Init, Plan, Dev, QA) that work in sequence with strict boundaries: planning personas interact with you to capture intent, while implementation personas run as isolated sub-agents that write code and tests autonomously. Features are tracked through a clear lifecycle (CREATED → DEV_READY → WIP → DONE), with automatic retry logic (up to 3 attempts) and failure analysis fed back into subsequent attempts. All specs live in .mash/plan/ as the single source of truth — immutable during development. Key features: - Interactive planning that asks clarifying questions before writing specs - Isolated dev and QA sub-agents with strict read/write boundaries - Git workflow options: per-feature worktrees or current branch - Auto-commit after QA pass, or manual git control - Feature retry with failure context propagation - Self-updating via /mash update