App lifecycle — from an idea to a product in production

The detailed path for a SaaS, by stage. Each stage says what it produces and when it is done; how to build it lives in the skills each stage points to. An agent that knows which stage it is in knows what to build, what not to build yet, what done means, and what to propose next.

The same lifecycle for any product, in eight steps and without the stack (start, proposal, a plan for a complex change, build with its reviews, the owner's click-through, the release review, release, real users), is what the owner gets by typing /product:start-here (Codex: $product:start-here). Discovery and the first prototype usually come from the propose skill: when its accepted proposal and prototype exist, they are stages 0 and 1's input, and the path starts at the brief or at design.

The path was learned building SaaS products with coding agents on Next.js (App Router) + Supabase Postgres + Clerk + Netlify, tested with Vitest and Playwright. A live Q&A product walked every stage first; a monitoring product and several others followed. The order, the done-whens and the rules that hold at every stage are general. Where a stage names a vendor, read the principle first and the vendor second, and substitute your own stack's equivalent.

What binds, in order

1. The owner. The owner decides what the product is, picks between options, approves the design, tries each stage and says go to a release. The agent proposes, builds and supplies evidence.
2. The product's own plan. Its phases, and each stage's done-when, are the product's. These stages are defaults a plan may merge, split or reorder, except in two ways: design is never dropped for screens (a plan that does setup first still runs the design stage, with its artboards, before any screen is built), and the front door (its block C) never moves behind the product's further feature phases (§ Order the work by what the owner will see).
3. The product section of the agent instructions, above all the shape it declares (below). Wherever this skill names something the shape says the product does not have, the shape wins and that part is skipped.
4. This skill's defaults, and the skills each stage points to for the how.

Find the stage you are in