Task #3: MVP API — payment-gated jobs + demo endpoint

OpenAPI spec (lib/api-spec/openapi.yaml)
- Added POST /jobs, GET /jobs/{id}, GET /demo endpoints
- Added schemas: CreateJobRequest, CreateJobResponse, JobStatusResponse,
  InvoiceInfo, JobState, DemoResponse, ErrorResponse
- Ran codegen: generated CreateJobBody, GetJobResponse, RunDemoQueryParams etc.

Jobs router (artifacts/api-server/src/routes/jobs.ts)
- POST /jobs: validates body, creates LNbits eval invoice, inserts job +
  invoice in a DB transaction, returns { jobId, evalInvoice }
- GET /jobs/🆔 fetches job, calls advanceJob() helper, returns state-
  appropriate payload (eval/work invoice, reason, result, errorMessage)
- advanceJob() state machine:
  - awaiting_eval_payment: checks LNbits, atomically marks paid + advances
    state via optimistic WHERE state='awaiting_eval_payment'; runs
    AgentService.evaluateRequest, branches to awaiting_work_payment or rejected
  - awaiting_work_payment: same pattern for work invoice, runs
    AgentService.executeWork, advances to complete
  - Any agent/LNbits error transitions job to failed

Demo router (artifacts/api-server/src/routes/demo.ts)
- GET /demo?request=...: in-memory rate limiter (5 req/hour per IP)
- Explicit guard for missing request param (coerce.string() workaround)
- Calls AgentService.executeWork directly, returns { result }

Dev router (artifacts/api-server/src/routes/dev.ts)
- POST /dev/stub/pay/:paymentHash: marks stub invoice paid in-memory
- Only mounted when NODE_ENV !== 'production'

Route index updated to mount all three routers

replit.md: documented full curl flow with all 6 steps, demo endpoint,
and dev stub-pay trigger

End-to-end verified with curl:
- Full flow: create → eval pay → evaluating → work pay → executing → complete
- Error cases: 400 on missing body/param, 404 on unknown job

artifacts/api-server/src/routes/dev.ts

@@ -0,0 +1,24 @@
+/**
+ * Development-only routes. Not mounted in production.
+ */
+import { Router, type Request, type Response } from "express";
+import { lnbitsService } from "../lib/lnbits.js";
+
+const router = Router();
+
+/**
+ * POST /dev/stub/pay/:paymentHash
+ * Marks a stub invoice as paid in the in-memory store.
+ * Only available when LNbitsService is in stub mode (i.e. no real LNbits creds).
+ */
+router.post("/dev/stub/pay/:paymentHash", (req: Request, res: Response) => {
+  const { paymentHash } = req.params as { paymentHash: string };
+  if (!lnbitsService.stubMode) {
+    res.status(400).json({ error: "Stub mode is not active. Real LNbits credentials are configured." });
+    return;
+  }
+  lnbitsService.stubMarkPaid(paymentHash);
+  res.json({ ok: true, paymentHash });
+});
+
+export default router;