feat(workflow): add fresh-agent Ralph tool

packages/workflow/workflow/README.md

@@ -10,7 +10,7 @@ The workflow seam (`ctx.workflows`) executes a model-written orchestration scrip
 
 A run is holder-owned. Engine-plugin unload prevents new starts but does not revoke accepted runs. The holder must call `dispose()` on every path; disposal cancels remaining work and reaches or abandons quiescence within the documented bound.
 
-`WorkflowStartRequest` contains `{ meta, script, args?, parent, signal? }`. `parent` attributes every child agent to the invoking agent. `meta` and `args` are plain data, not script fragments.
+`WorkflowStartRequest` contains `{ meta, script, args?, subagentProvider?, parent, signal? }`. `parent` attributes every child agent to the invoking agent. `subagentProvider` optionally routes every child in that run without exposing provider choice to the script; omission uses the engine's configured provider. `meta` and `args` are plain data, not script fragments.
 
 `WorkflowRun` exposes `{ id, meta, result, cancel(reason?), dispose() }`. `WorkflowResult` contains `{ value, stopReason, error?, agentsStarted }`; `value` is plain JSON data or `null`.
 

packages/workflow/workflow/src/types.ts

@@ -70,6 +70,12 @@ export interface WorkflowStartRequest {
   meta: WorkflowMeta
   /** Optional input exposed verbatim to the script as the `args` global. */
   args?: unknown
+  /**
+   * Optional engine-wide child-provider override for this run. The workflow
+   * script cannot observe or replace it; omission uses the engine's configured
+   * provider.
+   */
+  subagentProvider?: string
   /** The agent on whose behalf the run executes (parent of every child). */
   parent: Agent
   /** Cancels the run when aborted (the tool's `exec.signal`). */