Milestone

This skill writes:

• production/milestone.md

It does not create milestone directories, task lists, technical designs, prompt packs, or implementation files. Those belong to the downstream engineering workflow.

Phase 1: Validate Inputs

Fail if any of these are missing:

• design/gdd/game.md
• design/gdd/systems-index.md
• design/art/art-direction.md

Also stop if no system GDDs exist in design/gdd/ besides game.md and systems-index.md.

Read:

• design/gdd/game.md
• design/gdd/systems-index.md
• all existing design/gdd/*.md except game.md and systems-index.md
• all existing design/content/*-data.md
• all existing design/narrative/*.md
• design/art/art-direction.md
• all existing design/art/*-art.md
• .claude/docs/templates/plan/milestone.md
• production/milestone.md if exists

Phase 2: Hand Off To The Planner

Spawn gat-planner agent with all read content plus:

• instruction to write or update production/milestone.md
• instruction to split the project into ordered milestone handoff slices (M01, M02, ...)
• instruction not to create milestone directories, task lists, technical designs, prompt packs, or code
• planning focus from argument if provided

The planner should:

• choose a small set of meaningful milestones that can be handed off one stage at a time
• give each milestone a clear goal, player-facing outcome, and named system set
• define what is in scope and explicitly out of scope for each milestone
• include design, art, narrative, content, and risk context needed by a downstream engineering workflow
• avoid technical architecture, file plans, coding tasks, and implementation sequencing

Phase 3: Review

Summarize how many milestones were planned and which comes first.

Use AskUserQuestion:

• Start downstream engineering flow → Tell the user to hand the chosen milestone to their preferred engineering workflow
• Stop here