persona: retry transient 5xx on api requests

app/services/persona/api_service.rb

@@ -146,6 +146,11 @@ def connection
       request: { timeout: 30, open_timeout: 10 }
     ) do |f|
       f.request  :json
+      # persona throws the odd 5xx mid-fetch; one blip on the selfie lookup
+      # used to drop the liveness photos for good, since a saved document
+      # stops ensure_inquiry_data_saved from ever refetching. retry only
+      # touches idempotent methods, so creates/updates never double-fire.
+      f.request  :retry, max: 2, interval: 0.5, backoff_factor: 2, retry_statuses: [ 502, 503, 504 ]
       f.response :json
       f.adapter  Faraday.default_adapter
     end

spec/services/persona/api_service_spec.rb

@@ -214,6 +214,33 @@
       expect(result.liveness.map { |l| l[:label] }).to contain_exactly("selfie_center", "selfie_left", "selfie_right")
     end
 
+    it "retries a transient 503 before giving up on the selfie" do
+      stub = stub_request(:get, "#{base_url}/api/v1/verification/selfies/ver_selfie123")
+        .to_return({ status: 503, body: "" })
+        .then.to_return(
+          status: 200,
+          headers: { "Content-Type" => "application/json" },
+          body: { data: { id: "ver_selfie123", type: "verification/selfie", attributes: {
+            center_photo_url: "https://files.withpersona.com/center.jpg"
+          } }, meta: {} }.to_json
+        )
+
+      result = service.retrieve_verification_photos("ver_selfie123", type: "verification/selfie")
+
+      expect(stub).to have_been_requested.twice
+      expect(result.liveness.map { |l| l[:label] }).to eq([ "selfie_center" ])
+    end
+
+    it "raises Persona::APIError once 503 retries are exhausted" do
+      stub = stub_request(:get, "#{base_url}/api/v1/verification/selfies/ver_selfie123")
+        .to_return(status: 503, body: "")
+
+      expect {
+        service.retrieve_verification_photos("ver_selfie123", type: "verification/selfie")
+      }.to raise_error(Persona::APIError, /503/)
+      expect(stub).to have_been_requested.times(3)
+    end
+
     it "returns empty PhotoSet for non-selfie verifications" do
       result = service.retrieve_verification_photos("ver_gov123", type: "verification/government-id")