RoundWatch

Durable Algorand USDC payment monitoring for autonomous x402 workflows.

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RoundWatch watches one exact future Algorand MainNet USDC payment when no transaction ID exists yet. A caller defines the expected payment, pays a one-time x402 service fee, receives a durable watch ID, and can exit. RoundWatch persists the obligation and scan progress, then exposes verified on-chain evidence for later retrieval.

Production: Algorand MainNet · Circle USDC · x402 v2 · GoPlausible facilitator · Bazaar metadata live (catalog visibility under requalification) · remote MCP endpoint · durable restart recovery.

What it solves

A short-lived agent, job, or service may need to know whether a particular payment arrives after the caller has stopped running. Keeping that caller alive to poll an Algorand Indexer is unnecessary if a durable observer can own the wait instead.

RoundWatch lets a caller define the expected payment, purchase one watch through x402, and exit. The service persists the obligation, continues scanning Algorand, and records the matching transaction for later retrieval.

A backend that already operates durable Indexer or subscriber infrastructure may reasonably implement this itself. RoundWatch is for callers that do not want to own that operational component.

Lifecycle

1. The client submits the exact expected sender, receiver, atomic amount, and optional invoice note.
2. x402 returns payment requirements and the client signs the service payment locally.
3. GoPlausible verifies and settles the service payment.
4. RoundWatch activates the persisted watch only after the exact service-payment transaction is confirmed; that transaction's confirmed round becomes the scan baseline.
5. The caller may exit while RoundWatch polls the Algorand Indexer.
6. The watch becomes matched when an exact future USDC asset transfer appears.
7. The caller reads the durable result with GET /v1/watch/:id.

See Architecture for the normal, recovery, and matching paths.

See Operations for readiness, backup/restore, retention, and incident procedures.

See Roadmap for the current product direction and prioritization.

Live production service

The production server does not contain or need a wallet mnemonic or private key.

Economics v1 is live in production as of 2026-09-20 at 80ed94c746f2eac4a784a3738c6dbe8306ecfa3e. An external unsigned POST /v1/watch received HTTP 402 and verified MainNet, exact, ASA 31566704, the approved receiver, challenge tag, and amount 20000. The historical paid MainNet proof below remains evidence of the earlier 0.001 USDC contract.

API

Health and readiness

GET /health is liveness only. Use GET /ready to decide whether the durable service is ready for paid traffic. Render's platform health check must target /ready; /health must remain a lightweight process-liveness endpoint and must not be used as the paid-traffic readiness signal.

GET /health

Production response:

{
  "status": "ok",
  "purpose": "liveness",
  "network": "mainnet"
}

Readiness:

GET /ready

A ready production instance returns HTTP 200:

{
  "status": "ready",
  "network": "mainnet",
  "checks": {
    "storage": true,
    "backgroundWorkers": true
  }
}

Create a watch

POST /v1/watch
Content-Type: application/json

Example body:

{
  "idempotencyKey": "invoice-2026-09-16-001",
  "expectedSender": "3YFZ47IAKPB4H6B7U6MXI35HCAB5E6DA47UANIHOON53J7I5SMXUSYQXQQ",
  "expectedReceiver": "EQPLN32HPLPGBCNPOZUL6BL34CTNQGT3VAAMNAJWSIZGQ5CUNXOHB634XY",
  "atomicAmount": "1",
  "invoiceNote": "roundwatch:invoice-2026-09-16-001"
}

An ordinary request receives 402 Payment Required. An x402-capable client reads the payment requirements, signs the advertised service payment, and retries the same request. RoundWatch returns success only after settlement and durable activation succeed:

{
  "watchId": "f5d2fb6f-b224-4aae-989c-87a5418fd2ae",
  "workUnitBudget": 500,
  "eligibilityTtlMs": 1800000,
  "expiresAt": "2026-09-16T12:30:00.000Z",
  "message": "The watch is returned only if x402 settlement and durable activation succeed"
}

Request fields:

The watched asset is not a request field. The server selects the USDC ASA from its explicit network configuration: MainNet ASA 31566704 or TestNet ASA 10458941.

The server controls the lifetime, work budget, and admission policy. Before purchase, RoundWatch advertises the 30-minute eligibility window and 500-turn background work budget. The eligibility clock starts when the durable obligation is prepared, before x402 settlement completes, so settlement delay consumes part of that 30-minute window. Callers cannot override either bound. Passing the wall-clock deadline does not itself expire a watch; proof requires complete chain coverage through a closing checkpoint. If the work budget is exhausted first, the watch terminates as indeterminate with terminalReason=work_budget_exhausted, never as a false expired. At most 50 unfinished obligations may be open globally and at most 5 may be open for the verified service payer. Capacity exhaustion returns HTTP 429 before settlement.

Read a watch

GET /v1/watch/f5d2fb6f-b224-4aae-989c-87a5418fd2ae

The response is { "watch": ... }. This abridged matched example shows the stable consumer-facing fields; the live record also exposes settlement and scan metadata when available:

{
  "watch": {
    "id": "f5d2fb6f-b224-4aae-989c-87a5418fd2ae",
    "state": "matched",
    "expectedSender": "3YFZ47IAKPB4H6B7U6MXI35HCAB5E6DA47UANIHOON53J7I5SMXUSYQXQQ",
    "expectedReceiver": "EQPLN32HPLPGBCNPOZUL6BL34CTNQGT3VAAMNAJWSIZGQ5CUNXOHB634XY",
    "assetId": 31566704,
    "atomicAmount": "1",
    "invoiceNote": "roundwatch:invoice-2026-09-16-001",
    "createdAt": "2026-09-16T12:00:00.000Z",
    "expiresAt": "2026-09-16T12:30:00.000Z",
    "matchedTransaction": "VZKWYELPR4HHXPXM476NRLNU4JUKAEUUD4HGHFNAHDRD5IBFB2MA",
    "matchedRound": 65096073
  }
}

Unknown IDs return HTTP 404.

Watch states