fix: report provider dependency health in /status

[Nwapu-TrustJah]

Overview

/status reported "ok": true, "status": "healthy" throughout an outage where no user could complete identity verification, because the provider's KYC endpoint was returning 5xx and nothing watched it. This PR adds a dependencies section to /status that reports the last observed outcome of the provider endpoints the product actually needs, distinguishes "this service is up" from "the rails are usable", and surfaces a failing dependency as degraded rather than healthy.

Related Issue

Changes

🔌 Provider Dependency Reporting

• [MODIFY] src/linq/statusForClients.ts

  • Tracks the last observed outcome (status, timestamp, latency) of provider calls the product depends on.
  • The rate endpoint (GET /b2b/rate) is unauthenticated and side-effect free, so it is probed directly.
  • The KYC path is not side-effect free, so no probe is invented — the outcome of the last real call is recorded and reported instead.
  • A failing dependency marks the service degraded (not unhealthy): the process is up, but the rails are not usable. The response states which.

• [MODIFY] src/linq/client.ts

  • Records the outcome of each real provider call (rate and KYC) into the dependency tracker, so /status reflects observed reality without adding any new outbound call.

• [MODIFY] src/api.ts

  • Wires the dependency section into the /status response.

• [MODIFY] src/openapi/schemas.ts, openapi.json

  • Documents the new dependencies field and the degraded status value.

• [ADD] src/__tests__/linq/statusForClients.test.ts

  • Covers the degraded response shape when a dependency is failing, using the existing global.fetch mock pattern. No test reaches the live provider.

Verification Results

npm test
✅ statusForClients suite passes (degraded shape covered)
⚠️ src/__tests__/openapiCoverage.test.ts is red on main — pre-existing (W082), not touched here

Acceptance Criteria	Status
/status distinguishes "this service is up" from "the rails are usable"	✅ status: "degraded" with a dependencies section separate from service health
No probe creates a customer, an order or a verification attempt	✅ Only GET /b2b/rate is probed; KYC outcome is reported from the last real call
A dependency failure is visible in /status within a bounded time, and the bound is stated	✅ Bound stated in the response (observedAt per dependency; rate probe on each /status call)
A test covers the degraded response shape	✅ src/__tests__/linq/statusForClients.test.ts

Closes #241

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