feat: add E2B auto-pause support with pause/kill/reconnect provider lifecycle

Add `pause()`, `kill()`, and `reconnect()` methods to the SandboxProvider interface so providers can support graceful suspension and permanent deletion as distinct operations. The E2B provider now uses `betaCreate` with `autoPause: true` by default, `betaPause()` for suspension, and surfaces `SandboxDestroyedError` on reconnect to a deleted sandbox. SDK exposes `pauseSandbox()` and `killSandbox()` alongside the existing `destroySandbox()`.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/e2b/src/e2b.ts

@@ -0,0 +1,32 @@
+import { SandboxAgent } from "sandbox-agent";
+import { e2b } from "sandbox-agent/e2b";
+
+function collectEnvVars(): Record<string, string> {
+  const envs: Record<string, string> = {};
+  if (process.env.ANTHROPIC_API_KEY) envs.ANTHROPIC_API_KEY = process.env.ANTHROPIC_API_KEY;
+  if (process.env.OPENAI_API_KEY) envs.OPENAI_API_KEY = process.env.OPENAI_API_KEY;
+  return envs;
+}
+
+function inspectorUrlToBaseUrl(inspectorUrl: string): string {
+  return inspectorUrl.replace(/\/ui\/$/, "");
+}
+
+export async function setupE2BSandboxAgent(): Promise<{
+  baseUrl: string;
+  token?: string;
+  cleanup: () => Promise<void>;
+}> {
+  const client = await SandboxAgent.start({
+    sandbox: e2b({
+      create: { envs: collectEnvVars() },
+    }),
+  });
+
+  return {
+    baseUrl: inspectorUrlToBaseUrl(client.inspectorUrl),
+    cleanup: async () => {
+      await client.killSandbox();
+    },
+  };
+}