diff --git a/src/main/runtime/relay/relay-region-probe.test.ts b/src/main/runtime/relay/relay-region-probe.test.ts
new file mode 100644
index 00000000000..02c0e0f0b0c
--- /dev/null
+++ b/src/main/runtime/relay/relay-region-probe.test.ts
@@ -0,0 +1,29 @@
+import { readFileSync } from 'node:fs'
+import { describe, expect, it } from 'vitest'
+import { RELAY_REGIONS } from './relay-region-probe'
+
+// Read as text, not imported: `cloud/` is a separate pnpm workspace on a different zod major that
+// the desktop build never installs, so a TS import would not resolve here.
+const CONTRACT_SOURCE = readFileSync(
+  new URL('../../../../cloud/packages/relay-contract/src/relay-regions.ts', import.meta.url),
+  'utf8'
+)
+
+describe('RELAY_REGIONS', () => {
+  it('matches the relay contract exactly, region for region and in order', () => {
+    const declaration = /^export const RELAY_REGIONS = \[([^\]]+)\] as const$/m.exec(
+      CONTRACT_SOURCE
+    )
+    expect(
+      declaration,
+      'relay-regions.ts no longer declares RELAY_REGIONS as an inline array'
+    ).not.toBeNull()
+    const contractRegions = [...declaration![1].matchAll(/'([^']+)'/g)].map(([, region]) => region)
+    expect(contractRegions.length).toBeGreaterThan(0)
+
+    // A longer desktop list withholds the region hint fleet-wide (the catalog can never reach
+    // RELAY_REGIONS.length); a shorter one caches a hint won against an incomplete catalog. Order
+    // is pinned too because bestMeasurement breaks latency ties on the RELAY_REGIONS index.
+    expect([...RELAY_REGIONS]).toEqual(contractRegions)
+  })
+})