Add executor pool configuration documentation

Documents environment variables for code interpreter executor pool
configuration and removal of MAX_SIZE limits in version 0.3.4.

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Co-Authored-By: Claude <[email protected]>

Author: github-actions[bot]

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

@@ -239,9 +239,32 @@ await sandbox.exec("node app.js", {
 });
 ```
 
+## Code interpreter executor pool configuration
+
+The code interpreter maintains a pool of executor processes for running Python, JavaScript, and TypeScript code. Minimum pool sizes can be configured via environment variables in your Dockerfile:
+
+```dockerfile
+# Minimum number of warm executor processes (default: 3 for each language)
+ENV PYTHON_POOL_MIN_SIZE=3
+ENV JAVASCRIPT_POOL_MIN_SIZE=3
+ENV TYPESCRIPT_POOL_MIN_SIZE=3
+```
+
+The pool scales organically based on demand. There are no maximum pool size limits - new executors are created as needed to handle concurrent code execution contexts.
+
+:::note[Removed configuration options]
+Prior to version 0.3.4, the following environment variables were available but have been removed:
+- `PYTHON_POOL_MAX_SIZE`
+- `JAVASCRIPT_POOL_MAX_SIZE`
+- `TYPESCRIPT_POOL_MAX_SIZE`
+
+The pool now scales without artificial limits to ensure reliable execution across any number of concurrent code contexts.
+:::
+
 ## Related resources
 
 - [Wrangler configuration](/sandbox/configuration/wrangler/) - Setting Worker-level environment
 - [Secrets](/workers/configuration/secrets/) - Managing sensitive data
 - [Sessions API](/sandbox/api/sessions/) - Session-level environment variables
+- [Code Interpreter API](/sandbox/api/interpreter/) - Understanding code contexts
 - [Security model](/sandbox/concepts/security/) - Understanding data isolation