fix(sandbox): correct SDK examples and retry guidance

pages/sandbox/index.mdx

@@ -10,8 +10,8 @@ A real isolated computer for every agent. Each sandbox is a dev container or mic
 ## What you get
 
 - **A full machine per agent.** Run shell commands, read and write files, open ports, snapshot state, and attach a GPU only for the command that needs it.
-- **Any coding harness.** Each sandbox runs one AI backend: OpenCode (default), Claude Code, Codex, Cursor, and a dozen more. You pick it per sandbox.
-- **Durable agent sessions.** Dispatch a prompt and reconnect to the same run after a client crash, a deploy, or a browser reload. Same session ID is idempotent, so a retried request never re-executes.
+- **Any coding harness.** Choose the initial harness, such as OpenCode (default), Claude Code, or Codex, when you create a sandbox. Sessions can select different [supported harnesses](/infrastructure/harnesses).
+- **Durable agent sessions.** Dispatch a prompt and reconnect to the same run after a client crash, a deploy, or a browser reload. Store session and turn IDs for retries; completed work is deduplicated while its result remains cached.
 - **One key, metered per second.** The same [`sk-tan-` key](/platform/authentication) authenticates every call; you pay for what you use.
 
 ## Why use it
@@ -23,7 +23,7 @@ A real isolated computer for every agent. Each sandbox is a dev container or mic
 
 ## How it works
 
-Your SDK or CLI call hits the Sandbox API, which routes to a driver (container or microVM), provisions the machine, and relays the agent's output back to you as it streams. You never manage the infrastructure: `create` returns a machine, `delete` releases it. For the execution and orchestration internals, see the [runtime docs](/infrastructure/introduction).
+Your SDK and CLI calls hit the Sandbox API, which routes to a driver (container or microVM), provisions the machine, and relays the agent's output back to you as it streams. You never manage the infrastructure: `create` returns a machine, `delete` releases it. For the execution and orchestration internals, see the [runtime docs](/infrastructure/introduction).
 
 ## Use cases
 

pages/sandbox/quickstart.mdx

@@ -11,25 +11,58 @@ Create an isolated machine, run a shell command in it, then hand it to a coding
 
 ```bash
 npm install @tangle-network/sandbox
+npm install --save-dev tsx
 ```
 
 ## 2. Get an API key
 
 Create an `sk-tan-` key from [Authentication](/platform/authentication) and export it:
 
 ```bash
-export TANGLE_API_KEY=sk-tan-...
+read -rsp "Tangle API key: " TANGLE_API_KEY
+printf "\n"
+export TANGLE_API_KEY
 ```
 
 One key authenticates every Tangle product. Pass it to the client as `apiKey`; the SDK does not read env vars for you.
 
-## 3. Create a sandbox and run a command
+## 3. Check your credit and the service
+
+Free accounts start with no included credit.
+Add prepaid credit or select a plan with included credit at [id.tangle.tools](https://id.tangle.tools) before creating a sandbox.
+Agent model usage also draws from your balance.
+On the Free plan, sandboxes pause when the balance reaches zero.
+
+Check your key and available credit without provisioning a machine:
+
+```bash
+curl -fsS https://id.tangle.tools/v1/billing/balance \
+  -H "Authorization: Bearer ${TANGLE_API_KEY:?Set TANGLE_API_KEY}"
+```
+
+The response's `data.balance` is your available credit in US dollars.
+You can also check the service and available templates without creating a sandbox:
+
+```bash
+curl -fsS https://sandbox.tangle.tools/health
+curl -fsS https://sandbox.tangle.tools/v1/public-templates
+```
+
+Each TypeScript block below is a separate program for Node.js 22 or later.
+Run it in a project with the SDK installed and `TANGLE_API_KEY` exported.
+Save either block as `example.ts` and run it with `npx tsx example.ts`.
+Both examples release their machine after completion.
+
+## 4. Create a sandbox and run a command
 
 ```typescript
 import { Sandbox } from "@tangle-network/sandbox";
 
+const apiKey = process.env.TANGLE_API_KEY;
+if (!apiKey) throw new Error("Set TANGLE_API_KEY");
+
 const client = new Sandbox({
-  apiKey: process.env.TANGLE_API_KEY!,
+  apiKey,
   baseUrl: process.env.SANDBOX_BASE_URL ?? "https://sandbox.tangle.tools",
 });
 
@@ -45,14 +78,25 @@ try {
 
 `create` returns a live machine; `delete` releases it. You never provision infrastructure yourself.
 
-## 4. Run a coding agent
+## 5. Run a coding agent
 
-Each sandbox runs one coding harness. Choose it with `backend.type`. `opencode` (OpenCode) is the default and needs no extra key. `claude-code` (Claude Code) runs on Tangle Router by default with no extra key. To bring your own Anthropic credential, pass `backend: { type: 'claude-code', model: { apiKey: process.env.ANTHROPIC_API_KEY } }`. See [supported harnesses](/infrastructure/harnesses) for the full list.
+Choose the initial coding harness with `backend.type`.
+Sessions can select different [supported harnesses](/infrastructure/harnesses) in the same sandbox. `opencode` (OpenCode) is the default and needs no separate model-provider key. `claude-code` (Claude Code) runs on Tangle Router by default with no separate model-provider key. To bring your own Anthropic credential, pass `backend: { type: 'claude-code', model: { apiKey: process.env.ANTHROPIC_API_KEY } }`. See [supported harnesses](/infrastructure/harnesses) for the full list.
 
 ```typescript
+import { Sandbox } from "@tangle-network/sandbox";
+
+const apiKey = process.env.TANGLE_API_KEY;
+if (!apiKey) throw new Error("Set TANGLE_API_KEY");
+
+const client = new Sandbox({
+  apiKey,
+  baseUrl: process.env.SANDBOX_BASE_URL ?? "https://sandbox.tangle.tools",
+});
+
 const box = await client.create({
   environment: "universal",
-  backend: { type: "opencode" },
+  backend: { type: "opencode" }, // Also supports Claude Code, Codex, and other supported harnesses.
 });
 
 try {
@@ -63,16 +107,11 @@ try {
 }
 ```
 
-For runs that must survive a client crash or a browser reload, use `box.dispatchPrompt(message, { sessionId })` and reconnect with `box.session(sessionId)`. See [durable sessions in the SDK reference](/sandbox/sdk-reference).
-
-## 5. Check before you build (optional)
-
-These calls are safe to run without creating a sandbox:
-
-```bash
-curl -fsS https://sandbox.tangle.tools/health
-curl -fsS https://sandbox.tangle.tools/v1/public-templates
-```
+For durable runs, use `box.dispatchPrompt(message, { sessionId, turnId })` and reconnect with `box.session(sessionId)`.
+Store both IDs before dispatching and reuse them for retries of the same turn.
+Completed retries are deduplicated while their results remain cached.
+A session ID alone does not deduplicate completed retries.
+See [durable sessions in the SDK reference](/sandbox/sdk-reference).
 
 ## Next