status: don't call a site down if it never answered

DataLine NORD showed "not answering" from its first round. Its only
target, JustHost's "Moscow, DataLine" test IP, is listed but doesn't
answer from abroad at all, like most of JustHost's Russian test IPs
(only St Petersburg does). The control hosts sit on other networks, so
they couldn't flag it.

Mark a site down only if its targets answered at some point in the
24-hour window; one that never answered reads as unknown.

Assisted-by: Claude:opus-5-5

test/status_test.rb

@@ -29,6 +29,8 @@ class StatusTest < Minitest::Test
   end
 
   def two_buckets(base = B, **controls)
+    bucket(base - 3600, **controls) # the dark site answered an hour earlier
+    sample(@down, base - 3600, 5)
     [base - 300, base].each do |at|
       bucket(at, **controls)
       sample(@up, at, 5)
@@ -48,6 +50,11 @@ class StatusTest < Minitest::Test
     assert_equal 'ok', r.state
   end
 
+  def test_target_that_never_answered_is_unknown_not_down
+    [B - 300, B].each { |at| bucket(at); sample(@down, at, 0) }
+    assert_equal 'unknown', states(Bingo::Status.load(NOW))['dc-down']
+  end
+
   def test_one_dark_bucket_after_a_good_one_is_not_yet_down
     bucket(B - 300); sample(@down, B - 300, 5)
     bucket(B);       sample(@down, B, 0)