feat(sandbox-adapter): add Docker provider

docs/content/docs/sandboxes.mdx

@@ -1,6 +1,6 @@
 ---
 title: "Sandboxes"
-description: "Run an agent without a sandbox, or give it a shell in agentOS, E2B, Daytona, Freestyle, or a sandbox provider you write."
+description: "Run an agent without a sandbox, or give it a shell in agentOS, E2B, Daytona, Freestyle, Docker, or a sandbox provider you write."
 ---
 
 An agent doesn't need a sandbox. Without one, its file tools work on files in the Actor's own database. Add a sandbox only when the agent needs a shell.
@@ -83,6 +83,7 @@ agentOS needs no provider account. To use E2B or Daytona instead, see
 | <a href="https://e2b.dev" target="_blank" rel="noopener noreferrer">E2B</a> | `e2b` | Paused | Deleted |
 | <a href="https://daytona.io" target="_blank" rel="noopener noreferrer">Daytona</a> | `@daytonaio/sdk` | Stopped | Deleted |
 | <a href="https://freestyle.sh" target="_blank" rel="noopener noreferrer">Freestyle</a> | `freestyle` | Paused | Deleted |
+| <a href="https://docs.docker.com" target="_blank" rel="noopener noreferrer">Docker</a> | None. Uses the `docker` CLI. | Stopped | Removed |
 
 Provider credentials stay on your worker and never enter the sandbox.
 
@@ -148,6 +149,28 @@ npm add @rivet-dev/sandbox-adapter freestyle
 
 A Freestyle VM has no network access until a `firewall` rule allows it. Commands run as `root` through Python 3, so the image must include it. Every `freestyle/ubuntu*` snapshot does.
 
+### Docker
+
+For local development. The provider runs the `docker` CLI on your worker, so it uses the current Docker context.
+
+```sh
+npm add @rivet-dev/sandbox-adapter
+```
+
+<CodeSnippet file="examples/docs/sandboxes/docker.ts" title="server.ts" />
+
+| Option | Description |
+| --- | --- |
+| `image` | Image to run. It must include `/bin/sh`. Defaults to `ubuntu:24.04`. |
+| `cwd` | Working directory inside the container. Created when the Actor connects. Defaults to `/workspace`. |
+| `env` | Environment variables of the container. |
+| `network` | Docker network to join. Set `"none"` for no network access. Defaults to `bridge`. The `host` network is rejected. |
+| `ports` | Container ports to publish on a random `127.0.0.1` port. Read the address with `dockerPortAddress(sandboxId, port)`. |
+| `keepImageEntrypoint` | Runs the image's own entrypoint, for images such as `cloudflare/sandbox` that start a server. By default the container runs an idle process. |
+| `docker` | Path of the Docker CLI. Defaults to `docker`. |
+
+Each sandbox is one container with the label `dev.rivet.sandbox-adapter.sandbox-id`. The container has no host mounts, no host environment, no privileged mode, and no host network. A kill or timeout ends the command and every process it started.
+
 ## How the sandbox is managed
 
 - The sandbox is created the first time the agent needs it.

examples/docs/sandboxes/docker.ts

@@ -0,0 +1,19 @@
+import { createRegistry } from "@earendil-works/pi-durable";
+import { CodingTools } from "@earendil-works/pi-durable/tools";
+import { pi } from "@rivet-dev/pi";
+import { dockerProvider } from "@rivet-dev/sandbox-adapter/docker";
+import { setup } from "rivetkit";
+
+// read, write, edit, and bash, running in a local Docker container
+const extensions = createRegistry();
+extensions.install(CodingTools);
+
+const agent = pi({
+	model: "anthropic/claude-opus-5-5",
+	registry: extensions,
+	sandbox: dockerProvider({ image: "ubuntu:24.04" }),
+});
+
+export const registry = setup({ use: { agent } });
+
+registry.start();

packages/sandbox-adapter/package.json

@@ -15,6 +15,7 @@
 		"e2b",
 		"daytona",
 		"freestyle",
+		"docker",
 		"agent",
 		"ai",
 		"rivet",
@@ -45,6 +46,10 @@
 			"types": "./dist/daytona.d.ts",
 			"default": "./dist/daytona.js"
 		},
+		"./docker": {
+			"types": "./dist/docker.d.ts",
+			"default": "./dist/docker.js"
+		},
 		"./freestyle": {
 			"types": "./dist/freestyle.d.ts",
 			"default": "./dist/freestyle.js"
@@ -58,7 +63,8 @@
 	"types": "./dist/index.d.ts",
 	"scripts": {
 		"build": "tsc -p tsconfig.build.json",
-		"check-types": "tsc --noEmit"
+		"check-types": "tsc --noEmit",
+		"test": "vitest run"
 	},
 	"dependencies": {
 		"@earendil-works/chord": "^1.0.0",
@@ -85,7 +91,8 @@
 		"@types/node": "^24.0.0",
 		"e2b": "^2.51.0",
 		"freestyle": "^0.2.16",
-		"typescript": "^5.9.2"
+		"typescript": "^5.9.2",
+		"vitest": "3.2.7"
 	},
 	"engines": {
 		"node": ">=22.19.0"