feat(workflow): add fresh-agent Ralph tool

packages/workflow/workflow-workerthread/README.md

@@ -39,7 +39,7 @@ Unknown options, malformed arguments, unsupported schemas, tripped caps, provide
 For each `agent()` call:
 
 1. The worker sends `child-start` with a plain-data prompt and options.
-2. The host calls the configured provider through async `SubagentService.start`, passing the workflow's parent and one canonical per-run abort signal.
+2. The host calls the start request's provider override, or otherwise the configured provider, through async `SubagentService.start`, passing the workflow's parent and one canonical per-run abort signal. Provider choice applies to every child in that run and is not visible to the script.
 3. If start rejects, the host sends `child-start-error`; provider startup has already reached quiescence and no child lifecycle event is emitted.
 4. If start fulfills while the workflow still admits work, the host records the run, observes `result`, then sends `child-started`. Even an already-settled result is forwarded afterward, preserving start-before-result order.
 5. The worker emits paired `workflow/agent-start` and `workflow/agent-end` narration and requests child disposal after collection.
@@ -81,6 +81,8 @@ The host keeps a ledger of forwarded child starts. A graceful worker supplies th
 | `syncTimeoutMs` | `5000` | VM timeout for the script's initial synchronous slice. |
 | `disposeGraceMs` | `5000` | Bound before force-settlement/termination and for public disposal. |
 
+An owning consumer may set `WorkflowStartRequest.subagentProvider` for one run. This is an engine-level route, not a script hook or a model-facing option; the ordinary `workflow` tool leaves it unset.
+
 ## Model Experience
 
 ### Child-agent requests

packages/workflow/workflow-workerthread/src/index.ts

@@ -137,6 +137,7 @@ class WorkerWorkflowEngine extends WorkflowService {
     // the now-inactive engine fiber and break the seam's holder-owned lifetime.
     const runCtx = this.ctx
     const subagents = runCtx.subagents
+    const subagentProvider = request.subagentProvider ?? this.config.provider
     const workerRun = new WorkerRun(
       runCtx,
       subagents,
@@ -144,7 +145,7 @@ class WorkerWorkflowEngine extends WorkflowService {
       meta,
       request.parent,
       init,
-      this.config.provider,
+      subagentProvider,
       this.config.disposeGraceMs,
       {
         phase: (title) => { this.emitWorkflowEvent('workflow/phase', info, title) },

packages/workflow/workflow-workerthread/tests/built-worker.e2e.ts

@@ -27,16 +27,30 @@ import WorkerWorkflowEngine from '@deepseek-ai/dsh-workflow-workerthread'
 
 const ctx = new Context()
 await ctx.plugin(SubagentService)
-await ctx.plugin(WorkerWorkflowEngine, {})
+let selectedStarts = 0
+ctx.subagents.registerProvider({
+  name: 'built-selected',
+  capabilities: { outputSchema: true, depthLimit: false, toolFilter: false, persona: false },
+  inheritsParentContext: false,
+  async start() {
+    selectedStarts += 1
+    return {
+      id: 'built-child',
+      result: Promise.resolve({ output: [], structured: { answer: 42 }, stopReason: 'completed' }),
+      dispose: () => Promise.resolve(),
+    }
+  },
+})
+await ctx.plugin(WorkerWorkflowEngine, { provider: 'must-not-be-used' })
 const run = ctx.workflows.start({
-  script: 'return 6 * 7',
+  script: "const value = await agent('answer', { schema: { type: 'object', properties: { answer: { type: 'number' } }, required: ['answer'] } }); return value.answer",
   meta: { name: 'built-smoke', description: 'built worker smoke' },
-  // A zero-agent script never touches the provider.
+  subagentProvider: 'built-selected',
   parent: { id: 'built-smoke-parent', options: {} },
 })
 const result = await run.result
 await run.dispose()
-if (result.stopReason !== 'completed' || result.value !== 42) {
+if (result.stopReason !== 'completed' || result.value !== 42 || selectedStarts !== 1) {
   console.error('unexpected result: ' + JSON.stringify(result))
   process.exit(1)
 }

packages/workflow/workflow-workerthread/tests/workflow-workerthread.spec.ts

@@ -232,6 +232,26 @@ describe('dsh-workflow-workerthread', () => {
       expect(provider.runs[0]!.request.agentOptions).toEqual({ provider: 'openai' })
     })
 
+    it('a start-request provider override selects every child without changing the engine default', async () => {
+      const { ctx, parent, provider } = await setup()
+      const selected = new StubProvider('selected', () => text('selected reply'))
+      ctx.subagents.registerProvider(selected)
+
+      const overridden = ctx.workflows.start({
+        ...scripted("return await agent('route this run')"),
+        parent,
+        subagentProvider: 'selected',
+      })
+      expect((await overridden.result).value).toBe('selected reply')
+      await overridden.dispose()
+      expect(selected.runs).toHaveLength(1)
+      expect(provider.runs).toHaveLength(0)
+
+      const ordinary = await run(ctx, parent, scripted("return await agent('use the default')"))
+      expect(ordinary.value).toBe('stub reply')
+      expect(provider.runs).toHaveLength(1)
+    })
+
     it('a fatal hook error inside the worker kills the script and reports the error', async () => {
       const { ctx, parent } = await setup()
       const result = await run(ctx, parent, scripted("return await parallel([() => agent('x', { isolation: 'worktree' })])"))