diff --git a/test/test_orm_errors_jsonapi.rb b/test/test_orm_errors_jsonapi.rb
new file mode 100644
index 0000000..807d53e
--- /dev/null
+++ b/test/test_orm_errors_jsonapi.rb
@@ -0,0 +1,57 @@
+require 'minitest/autorun'
+require 'prism'
+
+class OrmErrorsJsonapiTest < Minitest::Test
+  def setup
+    @errors = Prism::Orm::Errors.new
+  end
+
+  def test_empty_errors_produce_empty_array
+    assert_equal [], @errors.to_jsonapi
+  end
+
+  def test_one_message_becomes_one_error_object
+    @errors.add(:title, "can't be blank")
+
+    entries = @errors.to_jsonapi
+    assert_equal 1, entries.size
+    entry = entries.first
+    assert_equal '422', entry[:status]
+    assert_equal({ pointer: '/data/attributes/title' }, entry[:source])
+    assert_equal "can't be blank", entry[:title]
+    assert_equal "title can't be blank", entry[:detail]
+  end
+
+  def test_custom_status_is_stringified
+    @errors.add(:base, 'is stale')
+
+    entry = @errors.to_jsonapi(status: 409).first
+    assert_equal '409', entry[:status]
+  end
+
+  def test_multiple_messages_on_same_attribute_each_get_their_own_entry
+    @errors.add(:body, 'is too short')
+    @errors.add(:body, 'contains banned words')
+
+    entries = @errors.to_jsonapi
+    assert_equal 2, entries.size
+    assert_equal ['is too short', 'contains banned words'], entries.map { |e| e[:title] }
+    assert(entries.all? { |e| e[:source] == { pointer: '/data/attributes/body' } })
+  end
+
+  def test_multiple_attributes_each_produce_their_own_pointer
+    @errors.add(:title, 'is too short')
+    @errors.add(:user_id, 'must be present')
+
+    entries = @errors.to_jsonapi
+    pointers = entries.map { |e| e[:source][:pointer] }
+    assert_includes pointers, '/data/attributes/title'
+    assert_includes pointers, '/data/attributes/user_id'
+  end
+
+  def test_full_messages_and_jsonapi_detail_stay_in_sync
+    @errors.add(:email, 'is invalid')
+
+    assert_equal @errors.full_messages, @errors.to_jsonapi.map { |e| e[:detail] }
+  end
+end
diff --git a/test/test_orm_giveaway_locking.rb b/test/test_orm_giveaway_locking.rb
new file mode 100644
index 0000000..86502fa
--- /dev/null
+++ b/test/test_orm_giveaway_locking.rb
@@ -0,0 +1,124 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+require 'fileutils'
+
+# Fast, deterministic, in-suite complement to blog_giveaway_demo.rb/
+# blog_giveaway_worker.rb (examples/blog's real "hard-capped giveaway"
+# feature, ClaimsController#create) - same read-count-then-decide-then-
+# write shape as Prism::Orm::Pessimistic's own counter tests
+# (test_orm_pessimistic.rb) and the acts_as_list swap-under-lock fix, but
+# for a "claim one of N limited slots" critical section specifically:
+# proves first that the race is real without a held lock (two racing
+# processes can BOTH believe they won the same last slot), then that
+# Model#with_lock rules it out entirely under genuinely concurrent OS
+# processes, not just threads.
+class OrmGiveawayLockingTest < Minitest::Test
+  def setup
+    @dir = Dir.mktmpdir('prism-giveaway-locking')
+    @store = Prism::Orm::Store.new(File.join(@dir, 'test.pstore'))
+    @store.create_table(:giveaways, %w[id slots claimed])
+
+    giveaway_class = Class.new(Prism::Orm::Model) { table_name :giveaways }
+    giveaway_class.store = @store
+    Object.const_set(:Giveaway, giveaway_class)
+  end
+
+  def teardown
+    FileUtils.remove_entry(@dir)
+    Object.send(:remove_const, :Giveaway) if Object.const_defined?(:Giveaway)
+  end
+
+  # Same rationale as test_orm_pessimistic.rb's own fork-based tests: real
+  # child OS processes sharing nothing but the PStore file on disk, so
+  # this is the same cross-process guarantee independent `prism` server
+  # processes pointed at the same database would get, not a simulation of
+  # it via threads. `exit!` (not `exit`), same reason as
+  # test_orm_pessimistic.rb: skip minitest/autorun's at_exit hook.
+  def test_claiming_without_a_lock_lets_two_racing_processes_both_win_the_last_slot
+    skip 'fork not supported on this platform' unless Process.respond_to?(:fork)
+
+    giveaway = Giveaway.create!(slots: 1, claimed: 0)
+    a_result = File.join(@dir, 'a_outcome')
+    b_result = File.join(@dir, 'b_outcome')
+    a_read, a_wrote_read_signal = IO.pipe
+    b_read, b_wrote_read_signal = IO.pipe
+
+    # Two pipes force the exact ordering an oversell needs: A reads the
+    # not-yet-claimed slot, THEN B reads it too (while it is still
+    # unclaimed, because A is blocked waiting on B before it writes
+    # anything back), THEN both independently decide "still free" and
+    # both write - each computing its own outcome from the SAME stale
+    # read, exactly like ClaimsController#create's giveaway_sold_out?
+    # check would without post.with_lock around it.
+    pid_a = Process.fork do
+      a_read.close
+      b_wrote_read_signal.close
+      record = Giveaway.find(giveaway.id)
+      a_wrote_read_signal.write('r')
+      a_wrote_read_signal.close
+      b_read.read(1)
+      b_read.close
+      outcome = record.claimed < record.slots ? :claimed : :sold_out
+      Giveaway.find(giveaway.id).update!(claimed: record.claimed + 1) if outcome == :claimed
+      File.write(a_result, outcome.to_s)
+      exit!(0)
+    end
+
+    pid_b = Process.fork do
+      a_wrote_read_signal.close
+      b_read.close
+      a_read.read(1)
+      a_read.close
+      record = Giveaway.find(giveaway.id)
+      b_wrote_read_signal.write('r')
+      b_wrote_read_signal.close
+      outcome = record.claimed < record.slots ? :claimed : :sold_out
+      Giveaway.find(giveaway.id).update!(claimed: record.claimed + 1) if outcome == :claimed
+      File.write(b_result, outcome.to_s)
+      exit!(0)
+    end
+
+    [a_read, a_wrote_read_signal, b_read, b_wrote_read_signal].each(&:close)
+    Process.waitpid(pid_a)
+    Process.waitpid(pid_b)
+
+    # The actual harm a real giveaway cares about: both processes decided
+    # THEY were the one who got the last slot - two winners for one prize -
+    # even though the persisted counter itself only ever reflects a single
+    # increment (same lost-update shape as Store#increment_counter's own
+    # unlocked callers), which would make the bug look survivable if this
+    # test only checked Giveaway#claimed afterward instead of what each
+    # racing process actually told its caller.
+    assert_equal 'claimed', File.read(a_result)
+    assert_equal 'claimed', File.read(b_result)
+  end
+
+  def test_claiming_through_with_lock_never_oversells_under_real_concurrent_processes
+    skip 'fork not supported on this platform' unless Process.respond_to?(:fork)
+
+    slots = 3
+    racers = 5
+    giveaway = Giveaway.create!(slots: slots, claimed: 0)
+
+    pids = racers.times.map do |i|
+      result_path = File.join(@dir, "outcome_#{i}")
+      Process.fork do
+        outcome = nil
+        Giveaway.find(giveaway.id).with_lock do |record|
+          outcome = record.claimed < record.slots ? :claimed : :sold_out
+          record.update!(claimed: record.claimed + 1) if outcome == :claimed
+        end
+        File.write(result_path, outcome.to_s)
+        exit!(0)
+      end
+    end
+
+    pids.each { |pid| Process.waitpid(pid) }
+
+    outcomes = racers.times.map { |i| File.read(File.join(@dir, "outcome_#{i}")) }
+    assert_equal slots, outcomes.count('claimed')
+    assert_equal racers - slots, outcomes.count('sold_out')
+    assert_equal slots, Giveaway.find(giveaway.id).claimed
+  end
+end