[LinuxDevil]

What changed

FlowExecutor runs a new executable node { type: 'agent', agent, input?, outputVariable? }: it sends the interpolated input (default '{{input}}') to the agent registered under FlowExecutionContext.agents[node.agent], and stores the reply text (a string, so durable checkpoints stay cloneable) in outputVariable.

• src/types/flow.ts: new AgentStepNode in RuntimeStep; StepNode JSDoc now points at agent steps.
• src/flows/FlowExecutor.ts: new exported FlowStepAgent (a createAgent() result fits as is), new FlowExecutionContext.agents map, agent handler + executeAgentStep, and the 'step' hint now reads ('step' is an editor shape: use { type: 'agent', agent, input } with FlowExecutionContext.agents).
• The step reuses llm-call/llm-response events carrying data.agent (the map's model/usage fields are now optional; existing data.model readers are unaffected). The agent's invoke_agent span nests under the node's flow.node agent span via parentSpanId.
• Unknown agent name → LOUSHO_FLOW_INVALID naming the registered keys; finishReason: 'awaiting-approval' → LOUSHO_FLOW_EXECUTION_FAILED (agent steps cannot pause a flow).
• Docs: docs/flows.md "Running an agent in a flow" shows the agent step first (tool-wrapping recipe kept as the alternative); agent added to the node table. llms-full.txt and api/* reports regenerated.
• Both new exports come through the existing export * barrels in src/flows/index.ts; no barrel edit needed.

How tested

• npx tsc --noEmit — clean
• npm run typecheck:tests — clean
• npm run test:types — 103 type tests pass
• npm run lint — clean
• npx vitest run src/flows — 297 tests, all pass (8 new in flowAgentStep.test.ts)
• npm run docs:verify-snippets -- --source-only — 341 snippets type-check
• npm run test:coverage — 6726 tests, all pass; first run failed 5 create-lousho-agent tests only because that workspace's dist/ was unbuilt locally (CI builds it first); they pass after npm run build --workspace=packages/create-lousho-agent
• npm run api:check, npm run docs:llms:check — clean
• npm run fallow — clean (0 dead exports, 0 above complexity)

Acceptance criteria

• sequence[agent(writer, '{{topic}}', 'draft'), return('$draft')] with agents: { writer: createAgent(...) } completes with 'A draft.'
• The writer's invoke_agent span's parentId is the flow.node agent span's id
• Unknown agent name → LOUSHO_FLOW_INVALID naming the available keys
• An agent whose tool needs approval (no approver) fails with LOUSHO_FLOW_EXECUTION_FAILED
• retry: { maxAttempts: 2 } retries a send that throws once
• A durable run resumed after the agent step does not call the agent again
• { type: 'step' } still fails with LOUSHO_FLOW_INVALID and the new hint

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