docs(deploy): document ARCADE_SUPERVISOR_MAX_CHILDREN [PLT-3801]

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: josebarrueta

app/en/operate/deploy/worker/page.mdx

@@ -62,6 +62,7 @@ Set these environment variables through `extraEnv`. See the [chart reference](ht
 | --- | --- | --- |
 | `ARCADE_PREWARM_TOOLKITS` | Unset | Comma-separated toolkits to start at boot and keep warm, by catalog name (`GoogleDocs`) or package name (`google-docs`). The worker logs and skips names the image doesn't offer. The chart sets this variable from `supervisor.prewarmToolkits`, so set one or the other, not both. |
 | `ARCADE_SERVE_TOOLKITS` | Unset | Comma-separated toolkits this worker serves. Unset, empty, or `*` serves the whole catalog the image offers. The chart sets this variable from `supervisor.serveToolkits`, so set one or the other, not both. |
+| `ARCADE_SUPERVISOR_MAX_CHILDREN` | `15` | The most runtimes running at once. `0` means unbounded. The chart always sets this variable from `supervisor.maxChildren`, so change that value instead of adding the variable to `extraEnv`. |
 | `ARCADE_SUPERVISOR_INVOKE_TIMEOUT` | 600 seconds | The longest a single tool call may run. |
 | `ARCADE_SUPERVISOR_PREWARM_CONCURRENCY` | `4` | How many runtimes start at once during boot. Keep it near the pod's core count. |