Support undefined/null as unset in setEnvVars

src/content/docs/sandbox/api/commands.mdx

@@ -25,6 +25,8 @@ const result = await sandbox.exec(command: string, options?: ExecOptions): Promi
   - `stream` - Enable streaming callbacks (default: `false`)
   - `onOutput` - Callback for real-time output: `(stream: 'stdout' | 'stderr', data: string) => void`
   - `timeout` - Maximum execution time in milliseconds
+  - `env` - Environment variables for this command: `Record<string, string | undefined>`
+  - `cwd` - Working directory for this command
 
 **Returns**: `Promise<ExecuteResponse>` with `success`, `stdout`, `stderr`, `exitCode`
 
@@ -43,6 +45,15 @@ await sandbox.exec('npm install', {
   stream: true,
   onOutput: (stream, data) => console.log(`[${stream}] ${data}`)
 });
+
+// With environment variables (undefined values are skipped)
+await sandbox.exec('node app.js', {
+  env: {
+    NODE_ENV: 'production',
+    PORT: '3000',
+    DEBUG_MODE: undefined  // Skipped, uses container default or unset
+  }
+});
 ```
 </TypeScriptExample>
 
@@ -94,7 +105,11 @@ const process = await sandbox.startProcess(command: string, options?: ProcessOpt
 - `command` - The command to start as a background process
 - `options` (optional):
   - `cwd` - Working directory
-  - `env` - Environment variables
+  - `env` - Environment variables: `Record<string, string | undefined>`
+  - `timeout` - Maximum execution time in milliseconds
+  - `processId` - Custom process ID
+  - `encoding` - Output encoding (default: `'utf8'`)
+  - `autoCleanup` - Whether to clean up process on sandbox sleep
 
 **Returns**: `Promise<Process>` object with:
 - `id` - Unique process identifier

src/content/docs/sandbox/api/sessions.mdx

@@ -26,7 +26,7 @@ const session = await sandbox.createSession(options?: SessionOptions): Promise<E
 **Parameters**:
 - `options` (optional):
   - `id` - Custom session ID (auto-generated if not provided)
-  - `env` - Environment variables for this session
+  - `env` - Environment variables for this session: `Record<string, string | undefined>`
   - `cwd` - Working directory (default: `"/workspace"`)
 
 **Returns**: `Promise<ExecutionSession>` with all sandbox methods bound to this session
@@ -42,7 +42,11 @@ const prodSession = await sandbox.createSession({
 
 const testSession = await sandbox.createSession({
   id: 'test',
-  env: { NODE_ENV: 'test', API_URL: 'http://localhost:3000' },
+  env: { 
+    NODE_ENV: 'test', 
+    API_URL: 'http://localhost:3000',
+    DEBUG_MODE: undefined  // Skipped, not set in this session
+  },
   cwd: '/workspace/test'
 });
 
@@ -123,11 +127,13 @@ Deleting a session immediately terminates all running commands. The default sess
 Set environment variables in the sandbox.
 
 ```ts
-await sandbox.setEnvVars(envVars: Record<string, string>): Promise<void>
+await sandbox.setEnvVars(envVars: Record<string, string | undefined>): Promise<void>
 ```
 
 **Parameters**:
-- `envVars` - Key-value pairs of environment variables to set
+- `envVars` - Key-value pairs of environment variables to set or unset
+  - `string` values: Set the environment variable
+  - `undefined` or `null` values: Unset the environment variable
 
 :::caution
 Call `setEnvVars()` **before** any other sandbox operations to ensure environment variables are available from the start.
@@ -141,7 +147,8 @@ const sandbox = getSandbox(env.Sandbox, 'user-123');
 await sandbox.setEnvVars({
   API_KEY: env.OPENAI_API_KEY,
   DATABASE_URL: env.DATABASE_URL,
-  NODE_ENV: 'production'
+  NODE_ENV: 'production',
+  OLD_TOKEN: undefined  // Unsets OLD_TOKEN if previously set
 });
 
 // Now commands can access these variables

src/content/docs/sandbox/configuration/environment-variables.mdx

@@ -30,6 +30,16 @@ await sandbox.exec("python seed.py"); // Has DATABASE_URL and API_KEY
 
 **Use when:** You need the same environment variables for multiple commands.
 
+**Unsetting variables**: Pass `undefined` or `null` to unset environment variables:
+
+```typescript
+await sandbox.setEnvVars({
+	API_KEY: 'new-key',     // Sets API_KEY
+	OLD_SECRET: undefined,  // Unsets OLD_SECRET
+	DEBUG_MODE: null        // Unsets DEBUG_MODE
+});
+```
+
 ### 2. Per-command with exec() options
 
 Pass environment variables for a specific command:
@@ -71,6 +81,56 @@ await session.exec("python seed.py");
 
 **Use when:** You need isolated execution contexts with different environment variables running concurrently.
 
+## Unsetting environment variables
+
+The Sandbox SDK supports unsetting environment variables by passing `undefined` or `null` values. This enables idiomatic JavaScript patterns for managing configuration:
+
+```typescript
+await sandbox.setEnvVars({
+	// Set new values
+	API_KEY: 'new-key',
+	DATABASE_URL: env.DATABASE_URL,
+
+	// Unset variables (removes them from the environment)
+	OLD_API_KEY: undefined,
+	TEMP_TOKEN: null
+});
+```
+
+**Before this change**: Passing `undefined` values would throw a runtime error.
+
+**After this change**: `undefined` and `null` values run `unset VARIABLE_NAME` in the shell.
+
+### Use cases for unsetting
+
+**Remove sensitive data after use:**
+
+```typescript
+// Use a temporary token
+await sandbox.setEnvVars({ TEMP_TOKEN: 'abc123' });
+await sandbox.exec('curl -H "Authorization: $TEMP_TOKEN" api.example.com');
+
+// Clean up the token
+await sandbox.setEnvVars({ TEMP_TOKEN: undefined });
+```
+
+**Conditional environment setup:**
+
+```typescript
+await sandbox.setEnvVars({
+	API_KEY: env.API_KEY,
+	DEBUG_MODE: env.NODE_ENV === 'development' ? 'true' : undefined,
+	PROFILING: env.ENABLE_PROFILING ? 'true' : undefined
+});
+```
+
+**Reset to system defaults:**
+
+```typescript
+// Unset to fall back to container's default NODE_ENV
+await sandbox.setEnvVars({ NODE_ENV: undefined });
+```
+
 ## Common patterns
 
 ### Pass Worker secrets to sandbox