fix(ralph): harden execution boundaries

packages/workflow/workflow/src/types.ts

@@ -76,6 +76,11 @@ export interface WorkflowStartRequest {
    * provider.
    */
   subagentProvider?: string
+  /**
+   * Optional per-run total-child ceiling. Implementations reject values above
+   * their deployment ceiling before publishing the run.
+   */
+  maxTotalAgents?: number
   /** The agent on whose behalf the run executes (parent of every child). */
   parent: Agent
   /** Cancels the run when aborted (the tool's `exec.signal`). */