feat: update billing-integration skill to lead with SDK usage

skills/billing-integration/SKILL.md

@@ -7,7 +7,9 @@ description: Wire Credyt billing into your application code. Adds customer creat
 
 Help the user wire Credyt into their application code. This skill works with the user's actual codebase — reading their existing code and adding Credyt integration in the right places.
 
-The full integration guide with code examples is at [docs.credyt.ai/ai-integration.md](https://docs.credyt.ai/ai-integration.md). Fetch it for detailed patterns and examples when needed.
+The full integration guide is at [docs.credyt.ai/ai-integration.md](https://docs.credyt.ai/ai-integration.md). Each section below links to its dedicated docs page, which includes HTTP, TypeScript, and Python examples — consult these if you need more detail on any integration area.
+
+> **Field naming:** The Credyt API uses `snake_case` for all fields. The TypeScript SDK maps these to `camelCase` automatically. The Python SDK keeps `snake_case`. Code samples in the linked docs show all three.
 
 ## Understand the codebase first
 
@@ -21,6 +23,27 @@ Check for:
 - Where the billable activities happen in their code
 - Existing environment variable patterns
 
+## Choose the integration approach
+
+Determine the right approach from context — only ask the user if you genuinely cannot tell.
+
+**Auto-detect (in order):**
+
+1. **Known AI platform** — Lovable, Bolt, Replit, and V0 all default to TypeScript. If running in one of these, use the TypeScript SDK.
+2. **Existing tech stack** — check the codebase scanned above. `package.json` → TypeScript/Node.js SDK. `requirements.txt` or `pyproject.toml` → Python SDK.
+3. **Unclear** → ask: *"Are you working in TypeScript/Node.js, Python, or another language?"* and lead with SDK options for the first two.
+
+Once determined, state the recommendation and give the user the option to override before writing any code:
+
+> "Based on your stack, I'll use the **TypeScript SDK** (`@credyt/api-client`). Let me know if you'd prefer Python or direct HTTP calls."
+
+SDK packages:
+- **TypeScript/Node.js** → `@credyt/api-client` (`npm install @credyt/api-client`)
+- **Python** → `credyt-api` (`pip install credyt-api`)
+- **Other language or preference for raw HTTP** → direct API calls with the `X-CREDYT-API-KEY` header
+
+The full SDK reference with examples for all three approaches is at [docs.credyt.ai/sdk](https://docs.credyt.ai/sdk).
+
 ## Integration areas
 
 Walk through each area. Not all will apply to every user — ask which ones they need.
@@ -29,23 +52,43 @@ Walk through each area. Not all will apply to every user — ask which ones they
 
 The Credyt API key must be stored securely on the server side — never in code that runs in the browser.
 
-Add `CREDYT_API_KEY` to their environment variables alongside their other secrets. Show them how to create an API client or helper that attaches the key as an `X-CREDYT-API-KEY` header.
+Add `CREDYT_API_KEY` to their environment variables alongside their other secrets, then initialise the client once and reuse it across requests.
+
+**TypeScript:**
+```typescript
+import { CredytApiClient } from "@credyt/api-client";
+const client = new CredytApiClient({ key: process.env.CREDYT_API_KEY! });
+```
+
+**Python:**
+```python
+from corehttp.credentials import ServiceKeyCredential
+from credytapi import CredytApiClient
 
-### 2. Customer creation (registration flow)
+client = CredytApiClient(
+    credential=ServiceKeyCredential(key=os.getenv("CREDYT_API_KEY")),
+)
+```
+
+**Direct HTTP:** Attach `X-CREDYT-API-KEY: <key>` to every request. Create a helper function or configured HTTP client instance that sets this header automatically.
+
+### 2. Customer creation — [docs](https://docs.credyt.ai/quickstart/create-a-customer)
 
 When a new user signs up in their app, create a matching Credyt customer. Find their registration/signup handler and add customer creation after successful account creation.
 
 Key points:
 - Use `external_id` to link the Credyt customer to their app's user ID
 - Subscribe the customer to the relevant products during creation
 - Store the Credyt customer ID in their database alongside the user record
-- Handle the case where the customer already exists (409/422 — look up by external_id instead)
+- Handle the case where the customer already exists (409/422 — look up by `external_id` instead)
+
+**SDK method:** `client.customers.create(...)`
 
 **Recurring fixed fees — pending subscriptions**
 
 If the product uses a recurring fixed fee (e.g. $20/month), the customer must pay upfront before their subscription activates. In this case the API returns a `pending` status rather than activating immediately.
 
-Set `return_url`, `failure_url`, and `redirect_to` on the subscription creation call so Credyt knows where to send the customer after payment — before you ever redirect them anywhere:
+Set `return_url`, `failure_url`, and `redirect_to` on the subscription so Credyt knows where to send the customer after payment:
 
 - `return_url` — where to send the customer after successful payment (e.g. `https://yourapp.com/account`)
 - `failure_url` — where to send them if payment fails (e.g. `https://yourapp.com/callbacks/payment-failed`)
@@ -59,50 +102,67 @@ When the response status is `pending`:
 
 Once the customer pays, Credyt fires a `subscription.activated` webhook. Listen for this event on your backend and use it to activate the user's account.
 
-### 3. Usage event tracking
+**Promotional or bundled signup credits**
+
+If the user's plan includes promotional credits (e.g. "start with $10 free") or bundled credits (e.g. 1,000 free API calls on signup), there are two ways to apply them:
+
+1. **One-off adjustment after customer creation** — credit the customer's wallet directly post-signup. Use this for simple, one-time promotional amounts. See [docs.credyt.ai/advanced-topics/adjustments-charges-gifts](https://docs.credyt.ai/advanced-topics/adjustments-charges-gifts).
+2. **Entitlements** — configure promotional credit as part of the product definition so it applies automatically on every new subscription. Use this for credits that are part of the standard plan offering. See [docs.credyt.ai/features/product-catalog/entitlements](https://docs.credyt.ai/features/product-catalog/entitlements).
+
+Ask the user whether they want to include signup credits, and if so which approach fits their use case.
+
+### 3. Usage event tracking — [docs](https://docs.credyt.ai/quickstart/send-usage)
 
 Find where the billable activities happen in their code and add event submission after each one. Each event needs:
 
 - A unique ID (UUID) so the same event can't be billed twice
 - The correct `event_type` matching the product configuration
-- A timestamp of when it happened
+- A timestamp of when it happened (`occurred_at`)
 - Any data fields needed for pricing (volume fields, dimensions)
 
+**SDK method:** `client.events.sendUsage(...)` (TS) or `client.events.send_usage(...)` (Python).
+
 For **volume-based** products, the event data must include the volume field (e.g., `total_tokens: 1500`).
 For **dimensional** products, include the dimension values (e.g., `model: "gpt-4"`).
 
-### 4. Cost tracking (if they set up vendors)
+### 4. Cost tracking — [docs](https://docs.credyt.ai/features/profitability)
 
 If the user set up vendors in `/credyt:billing-setup`, add cost data to usage events. Each event can include a `costs` array with the vendor ID, the amount it cost, and the currency.
 
 This is typically added right after the billable action completes, when the cost is known (e.g., after receiving the response from an AI API that includes token counts).
 
 > "Even if you're not charging users yet, attaching costs to every event lets Credyt calculate your unit economics so you can make pricing decisions based on real data."
 
-### 5. Balance checks (pre-action gating)
+### 5. Balance checks — [docs](https://docs.credyt.ai/quickstart/check-balance)
 
 Before expensive operations, check the customer's wallet balance. If insufficient, block the action and prompt the user to top up.
 
+**SDK method:** `client.wallets.customerWalletOps.getCustomerWallet(customerId)` to fetch the full wallet, or `client.wallets.customerWalletOps.getAccount(customerId, "accountName:ASSET")` to check a specific account balance.
+
 Find where billable actions are initiated (API routes, button handlers, etc.) and add a balance check before the action runs. Return a clear message if the balance is too low.
 
-Show them how to estimate the cost of the upcoming action and compare it against the available balance.
+Estimate the cost of the upcoming action and compare it against the available balance.
 
-### 6. Billing portal / top-up UI
+### 6. Billing portal / top-up UI — [docs](https://docs.credyt.ai/quickstart/billing-portal)
 
 Help users add funds through Credyt's billing portal. This is the simplest way to handle payments — Credyt hosts the page, handles Stripe, and redirects back to their app.
 
 Add a "Billing" or "Add funds" link/button in their app's settings or account page. When clicked, the backend creates a billing portal session and redirects the user to the URL.
 
+**SDK method:** `client.billingPortal.createPortalSession(...)`
+
 Key points:
 - Portal sessions expire after 10 minutes
-- Set a `return_url` for where to send users after they're done
-- Set a `failure_url` for payment failures
+- Set `return_url` for where to send users after they're done
+- Set `failure_url` for payment failures
 
-### 7. Balance display
+### 7. Balance display — [docs](https://docs.credyt.ai/quickstart/check-balance)
 
 Show the user's current balance in the app UI. Fetch from the wallet endpoint and display the available amount.
 
-Consider where this fits in their app — sidebar, header, account page — and add it there.
+**SDK method:** `client.wallets.customerWalletOps.getCustomerWallet(customerId)`.
+
+Decide where this fits in their app — sidebar, header, account page — and add it there.
 
 ## Implementation approach
 
@@ -122,6 +182,7 @@ After each piece, suggest they test it:
 
 For detailed code examples, error handling patterns, and advanced topics (hybrid billing, refunds, auto top-up), point the user to:
 
+- **SDK reference** (TypeScript & Python): [docs.credyt.ai/sdk](https://docs.credyt.ai/sdk)
 - **Full integration guide**: [docs.credyt.ai/ai-integration.md](https://docs.credyt.ai/ai-integration.md)
 - **API reference**: [docs.credyt.ai](https://docs.credyt.ai)
 - **Examples**: [github.com/credyt/learn](https://github.com/credyt/learn)