Ignore pod shutdown errors in ErrorTracker

Add ErrorTrackerIgnorer to drop port_died, write_failed, epipe, and
broken pipe errors that occur during K8s pod shutdown. Same patterns
already filtered by HoneybadgerFilter and LoggerFilters.

config/config.exs

@@ -12,7 +12,8 @@ config :elixir, :time_zone_database, Tzdata.TimeZoneDatabase
 
 config :error_tracker,
   repo: Towerops.Repo,
-  otp_app: :towerops
+  otp_app: :towerops,
+  ignorer: Towerops.ErrorTrackerIgnorer
 
 # Configure esbuild (the version is required)
 config :esbuild,

lib/towerops/error_tracker_ignorer.ex

@@ -0,0 +1,24 @@
+defmodule Towerops.ErrorTrackerIgnorer do
+  @moduledoc """
+  Drops benign errors from ErrorTracker that occur during K8s pod shutdown.
+
+  Matches the same patterns as `Towerops.HoneybadgerFilter` and
+  `Towerops.LoggerFilters.drop_shutdown_errors/2`.
+  """
+
+  @behaviour ErrorTracker.Ignorer
+
+  @impl true
+  def ignore?(%ErrorTracker.Error{reason: reason}, _context) do
+    shutdown_error?(reason)
+  end
+
+  defp shutdown_error?(reason) when is_binary(reason) do
+    String.contains?(reason, "port_died") or
+      String.contains?(reason, "write_failed") or
+      String.contains?(reason, "epipe") or
+      String.contains?(reason, "broken pipe")
+  end
+
+  defp shutdown_error?(_), do: false
+end

test/towerops/error_tracker_ignorer_test.exs

@@ -0,0 +1,45 @@
+defmodule Towerops.ErrorTrackerIgnorerTest do
+  use ExUnit.Case, async: true
+
+  alias Towerops.ErrorTrackerIgnorer
+
+  defp build_error(reason) do
+    %ErrorTracker.Error{
+      kind: "ErlangError",
+      reason: reason,
+      source_line: "-",
+      source_function: "-",
+      status: :unresolved,
+      fingerprint: "abc",
+      last_occurrence_at: DateTime.utc_now(),
+      muted: false
+    }
+  end
+
+  describe "ignore?/2" do
+    test "ignores port_died errors" do
+      error = build_error("Erlang error: {:port_died, :normal}")
+      assert ErrorTrackerIgnorer.ignore?(error, %{})
+    end
+
+    test "ignores write_failed errors" do
+      error = build_error("{:write_failed, :standard_io, :enoent}")
+      assert ErrorTrackerIgnorer.ignore?(error, %{})
+    end
+
+    test "ignores epipe errors" do
+      error = build_error("{:error, {:write_failed, %{type: :standard_io}, {:badarg, :epipe}}}")
+      assert ErrorTrackerIgnorer.ignore?(error, %{})
+    end
+
+    test "ignores broken pipe errors" do
+      error = build_error("broken pipe (epipe)")
+      assert ErrorTrackerIgnorer.ignore?(error, %{})
+    end
+
+    test "does not ignore regular errors" do
+      error = build_error("something went wrong")
+      refute ErrorTrackerIgnorer.ignore?(error, %{})
+    end
+  end
+end