chore: import upstream snapshot with attribution

.changeset/README.md

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+# Changesets
+
+To add changeset run: 
+    
+```bash
+npx changeset
+```
+
+in the root of the project. This will create a new changeset in the `.changeset` folder.

.changeset/config.json

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+{
+  "$schema": "https://unpkg.com/@changesets/config@2.3.1/schema.json",
+  "changelog": "@changesets/cli/changelog",
+  "commit": false,
+  "fixed": [],
+  "ignore": [],
+  "linked": [],
+  "access": "public",
+  "baseBranch": "main",
+  "updateInternalDependencies": "patch",
+  "privatePackages": {
+    "version": true,
+    "tag": true
+  }
+}

.changeset/js-connectrpc-stable.md

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+---
+"e2b": patch
+---
+
+Move the Connect/Protobuf runtime dependencies off the `2.0.0-rc.3` pre-release pin to the stable line: `@connectrpc/connect` and `@connectrpc/connect-web` upgrade to `^2.1.2`, and `@bufbuild/protobuf` upgrades from `^2.6.2` to `^2.12.1`. No public API changes — the sandbox filesystem and command RPCs continue to use the same Connect transport configuration.

.changeset/set-integration-once.md

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+---
+"e2b": minor
+"@e2b/python-sdk": minor
+---
+
+Replace the per-call `integration` connection option with a set-once, process-wide `ConnectionConfig.setIntegration()` (JS) / `ConnectionConfig.set_integration()` (Python). Integrations wrapping the SDK call it once at startup and every request is attributed via the `User-Agent` header — no more threading the option through individual SDK calls. The method is internal and hidden from docs. The `integration` option on `ConnectionConfigOpts` (JS) and the `integration` keyword argument on `ConnectionConfig` (Python) are removed; `ConnectionConfigOpts` remains as a deprecated alias of `ConnectionOpts`. In both SDKs, an explicitly provided `User-Agent` header now always takes precedence over the SDK-built one, while SDK-built values are recomputed whenever a config is rebuilt so they always reflect the current integration.

.changeset/switch-to-tsdown.md

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+---
+"@e2b/cli": patch
+"e2b": patch
+---
+
+Switch the build tooling from `tsup` to `tsdown`. The published artifacts are unchanged: the SDK still ships `dist/index.js` (CJS), `dist/index.mjs` (ESM) and `dist/index.d.ts`/`dist/index.d.mts`, and the CLI still ships an executable `dist/index.js` with its `dist/templates`.
+
+`engines.node` for both packages is set to `>=20.18.1 <21 || >=22` (Node 20.18.1+, or 22 and above — keeping the minimum required by `undici` while excluding the end-of-life Node 21 line).