Setup prompt for AI coding agents

You are helping me set up UsageGate for my SaaS product.

## What UsageGate is
UsageGate is a usage-billing / feature-gating control plane. I (the SaaS founder) define plans → features → limits. My backend asks UsageGate whether *my* end users can access a feature and how many credits they have left. End users never log into UsageGate.

Stripe is required: I keep Checkout in *my* Stripe account. UsageGate listens to webhooks, refills balances from subscription metadata, and sets resetAt from the subscription's current_period_end. There is no calendar cron that auto-tops balances — the period clock is Stripe's.

## Goals for this session
1. Design a Plan → Feature → Limit rules graph for my product
2. Choose stable feature keys my code will call forever
3. Wire GateClient into my backend (canAccess / consume / grant)
4. Connect Stripe webhooks (required) so paid renewals refill + set period end
5. Leave me with env vars, code snippets, and a smoke-test checklist

## Product context (fill this in before you start)
- Product name:
- What users do that costs credits or should be gated:
- Free tier limits:
- Paid tier(s) and limits:
- Stripe billing interval (monthly / yearly / other):
- End-user id field in my app (e.g. session.user.id):
- Stack (Next.js / Express / other):
- UsageGate base URL (local default http://127.0.0.1:43123):
- I already have an API key? (yes/no):
- Stripe webhook secret ready? (yes/no):

## Rules you must follow
- Never invent a second login system. userId = my existing user id.
- Feature keys: snake_case, stable (ai_credits, export_pdf, seats).
- Prefer METERED for burnable credits, BOOLEAN for on/off, NUMERIC_LIMIT for caps (seats/projects).
- canAccess / consume default fail-open — note that when discussing reliability.
- grant() is absolute set (not increment). Use grant for free signup / trials / admin overrides only.
- Paid refills and period boundaries MUST go through Stripe webhooks — do not treat Stripe as optional.
- Explain resetAt: after current_period_end, effective balance is 0 until the next invoice.paid sets a new balance + new resetAt. Leftover credits do not roll over.
- Do not put the API key in frontend code. Server-side only.
- Package: @usagegate0/sdk → new GateClient(process.env.USAGEGATE_KEY!, { baseUrl: process.env.USAGEGATE_API_BASE_URL })

## Suggested workflow
1. Ask me the product-context blanks if empty.
2. Propose a rules graph (nodes + edges) I can paste into dashboard or gate.putRules().
3. Show grant on signup for free-tier balances (optional resetAt for trials).
4. Show the gate on my expensive code path (canAccess → work → consume).
5. Stripe (required): webhook URL POST {baseUrl}/api/webhooks/stripe, save whsec via dashboard or gate.configureStripe(), subscription.metadata with end_user_id + feature_grants JSON. Remind me that resetAt comes from current_period_end.
6. Give a checklist: create key, set env, save rules, configure Stripe, grant test user OR trigger invoice.paid, hit the gated route, watch /dashboard.

## HTTP cheat sheet (if not using SDK)
Authorization: Bearer <api_key>
GET  /api/v1/check?userId=&feature=
POST /api/v1/consume  { userId, feature, amount }
POST /api/v1/grant    { userId, feature, balance, resetAt? }
GET|PUT /api/v1/rules
POST /api/webhooks/stripe  (Stripe-Signature)

Start by confirming my product context, then propose the rules graph.