fix: retry firmware fetch with exponential backoff on network errors

Increase max_attempts from 3 to 10 and add custom backoff/1 that uses
quadratic growth (attempt² × 60s) capped at 2 hours, so transient
network failures retry over ~9 hours rather than being discarded after
3 quick attempts.

lib/towerops/workers/firmware_version_fetcher_worker.ex

@@ -5,7 +5,7 @@ defmodule Towerops.Workers.FirmwareVersionFetcherWorker do
   Runs daily to check for new firmware releases and updates the firmware_releases table.
   """
 
-  use Oban.Worker, queue: :maintenance, max_attempts: 3
+  use Oban.Worker, queue: :maintenance, max_attempts: 10
 
   import SweetXml
 
@@ -13,6 +13,11 @@ defmodule Towerops.Workers.FirmwareVersionFetcherWorker do
 
   require Logger
 
+  @impl Oban.Worker
+  def backoff(%Oban.Job{attempt: attempt}) do
+    min(attempt * attempt * 60, 7_200)
+  end
+
   @rss_url "https://cdn.mikrotik.com/routeros/latest-stable.rss"
   @changelog_url "https://mikrotik.com/download/changelogs"
 

test/towerops/workers/firmware_version_fetcher_worker_test.exs

@@ -20,6 +20,26 @@ defmodule Towerops.Workers.FirmwareVersionFetcherWorkerTest do
     end
   end
 
+  describe "backoff/1" do
+    test "early attempts have shorter delays than later attempts" do
+      attempt_1 = FirmwareVersionFetcherWorker.backoff(%Oban.Job{attempt: 1})
+      attempt_5 = FirmwareVersionFetcherWorker.backoff(%Oban.Job{attempt: 5})
+      assert attempt_1 < attempt_5
+    end
+
+    test "backoff is capped at 2 hours" do
+      high_attempt = FirmwareVersionFetcherWorker.backoff(%Oban.Job{attempt: 100})
+      assert high_attempt <= 7_200
+    end
+
+    test "all attempts return positive values" do
+      for attempt <- 1..10 do
+        backoff = FirmwareVersionFetcherWorker.backoff(%Oban.Job{attempt: attempt})
+        assert backoff > 0, "attempt #{attempt} returned non-positive backoff"
+      end
+    end
+  end
+
   describe "parse_rss_feed/1" do
     test "parses valid RSS feed XML" do
       valid_rss = """