diff --git a/test/test_orm_index.rb b/test/test_orm_index.rb
index 94704c8..c00380d 100644
--- a/test/test_orm_index.rb
+++ b/test/test_orm_index.rb
@@ -794,3 +794,191 @@ class OrmIndexEqualityRangeStoreTest < Minitest::Test
     wide.insert(:tasks, project: 'a', priority: 'high', position: 1)
     wide.insert(:tasks, project: 'a', priority: 'high', position: 2)
 
+    declared_order = wide.lookup_by_index_equality_range(:tasks, { project: 'a', priority: 'high' }, :position, gte: 0)
+    reversed_order = wide.lookup_by_index_equality_range(:tasks, { priority: 'high', project: 'a' }, :position, gte: 0)
+    assert_equal [1, 2], declared_order.map { |row| row['position'] }.sort
+    assert_equal declared_order.map { |row| row['id'] }.sort, reversed_order.map { |row| row['id'] }.sort
+  end
+
+  def test_backfills_from_existing_rows
+    @store.insert(:posts, featured: true, position: 1)
+    @store.insert(:posts, featured: true, position: 2)
+    @store.add_index(:posts, %i[featured position])
+
+    matches = @store.lookup_by_index_equality_range(:posts, { 'featured' => true }, :position, gte: 2)
+    assert_equal [2], matches.map { |row| row['position'] }
+  end
+
+  def test_tracks_inserts_updates_and_deletes
+    @store.add_index(:posts, %i[featured position])
+    a = @store.insert(:posts, featured: true, position: 1)
+    @store.insert(:posts, featured: true, position: 2)
+
+    assert_equal [1, 2], @store.lookup_by_index_equality_range(:posts, { 'featured' => true }, :position,
+                                                                gte: 0).map { |r| r['position'] }.sort
+
+    @store.update(:posts, a, position: 9)
+    assert_equal [2, 9], @store.lookup_by_index_equality_range(:posts, { 'featured' => true }, :position,
+                                                                gte: 0).map { |r| r['position'] }.sort
+
+    @store.delete(:posts, a)
+    assert_equal [2], @store.lookup_by_index_equality_range(:posts, { 'featured' => true }, :position,
+                                                             gte: 0).map { |r| r['position'] }
+  end
+
+  def test_switching_the_prefix_value_moves_a_row_to_the_other_partition
+    @store.add_index(:posts, %i[featured position])
+    id = @store.insert(:posts, featured: true, position: 1)
+
+    @store.update(:posts, id, featured: false)
+    assert_equal [], @store.lookup_by_index_equality_range(:posts, { 'featured' => true }, :position, gte: 0)
+    assert_equal [1], @store.lookup_by_index_equality_range(:posts, { 'featured' => false }, :position,
+                                                             gte: 0).map { |r| r['position'] }
+  end
+
+  def test_an_unknown_prefix_value_matches_nothing_without_a_scan
+    @store.add_index(:posts, %i[featured position])
+    @store.insert(:posts, featured: true, position: 1)
+
+    assert_equal [], @store.lookup_by_index_equality_range(:posts, { 'featured' => 'nonexistent' }, :position, gte: 0)
+  end
+
+  def test_a_three_column_composite_index_still_works_with_a_two_column_prefix
+    @store = Prism::Orm::Store.new(File.join(@dir, 'wide.pstore'))
+    @store.create_table(:tasks, %w[id project priority position])
+    @store.add_index(:tasks, %i[project priority position])
+    @store.insert(:tasks, project: 'a', priority: 'high', position: 1)
+    @store.insert(:tasks, project: 'a', priority: 'high', position: 2)
+    @store.insert(:tasks, project: 'a', priority: 'low', position: 1)
+
+    matches = @store.lookup_by_index_equality_range(:tasks, { project: 'a', priority: 'high' }, :position, gte: 0)
+    assert_equal [1, 2], matches.map { |row| row['position'] }.sort
+  end
+
+  def test_lookup_by_index_range_still_refuses_a_composite_index_unchanged_behavior
+    @store.add_index(:posts, %i[featured position])
+    @store.insert(:posts, featured: true, position: 1)
+    assert_nil @store.lookup_by_index_range(:posts, :position, gte: 0)
+  end
+
+  # A paranoid model's Model.all already carries `where(deleted_at: nil)`
+  # before any caller-added `.where(featured: ...)` - real regression this
+  # session's blog_demo.rb run caught: the index prefix is only `featured`,
+  # so `equalities` legitimately arrives with an EXTRA column
+  # (`deleted_at`) the index knows nothing about. That must still resolve
+  # through the index (using only the subset it actually covers), not fall
+  # back to a scan just because the caller happened to also constrain an
+  # unrelated column.
+  def test_an_equality_column_outside_the_index_prefix_does_not_block_the_lookup
+    @store.add_index(:posts, %i[featured position])
+    @store.insert(:posts, featured: true, position: 1, deleted_at: nil)
+    @store.insert(:posts, featured: true, position: 5, deleted_at: nil)
+
+    matches = @store.lookup_by_index_equality_range(:posts, { 'deleted_at' => nil, 'featured' => true },
+                                                      :position, lt: 3)
+    assert_equal [1], matches.map { |row| row['position'] }
+  end
+
+  def test_the_most_specific_covering_composite_index_wins_when_several_could_answer
+    wide = Prism::Orm::Store.new(File.join(@dir, 'multi.pstore'))
+    wide.create_table(:tasks, %w[id project priority position])
+    wide.add_index(:tasks, %i[project position])
+    wide.add_index(:tasks, %i[project priority position])
+    wide.insert(:tasks, project: 'a', priority: 'high', position: 1)
+    wide.insert(:tasks, project: 'a', priority: 'low', position: 2)
+
+    matches = wide.lookup_by_index_equality_range(:tasks, { project: 'a', priority: 'high' }, :position, gte: 0)
+    assert_equal [1], matches.map { |row| row['position'] },
+                 'the 3-column index covering priority too should be preferred over the 2-column one'
+  end
+end
+
+class OrmIndexEqualityRangeRelationTest < Minitest::Test
+  def setup
+    @dir = Dir.mktmpdir('prism-index-eq-range-relation')
+    @store = CountingIndexStore.new(File.join(@dir, 'test.pstore'))
+    @store.create_table(:posts, %w[id featured position])
+    @store.add_index(:posts, %i[featured position])
+
+    post_class = Class.new(Prism::Orm::Model) { table_name :posts }
+    post_class.store = @store
+    Object.const_set(:EqRangeIndexedPost, post_class)
+
+    EqRangeIndexedPost.create!(featured: true, position: 1)
+    EqRangeIndexedPost.create!(featured: true, position: 2)
+    EqRangeIndexedPost.create!(featured: true, position: 3)
+    EqRangeIndexedPost.create!(featured: false, position: 1)
+    EqRangeIndexedPost.create!(featured: false, position: 2)
+  end
+
+  def teardown
+    FileUtils.remove_entry(@dir)
+    Object.send(:remove_const, :EqRangeIndexedPost) if Object.const_defined?(:EqRangeIndexedPost)
+  end
+
+  def test_two_chained_wheres_scope_equality_then_range_never_scan
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(featured: true).where(position: { lt: 3 }).order(:position).to_a
+    assert_equal [1, 2], results.map { |p| p['position'] }
+    assert_equal 0, @store.scan_count
+    assert_equal 1, @store.eq_range_hits
+  end
+
+  def test_single_where_with_both_conditions_in_one_hash_never_scans
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(featured: true, position: { gte: 2 }).to_a
+    assert_equal [2, 3], results.map { |p| p['position'] }.sort
+    assert_equal 0, @store.scan_count
+    assert_equal 1, @store.eq_range_hits
+  end
+
+  def test_a_ruby_range_value_alongside_an_equality_uses_the_composite_index
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(featured: false).where(position: 1..1).to_a
+    assert_equal [1], results.map { |p| p['position'] }
+    assert_equal 0, @store.scan_count
+  end
+
+  def test_the_other_scope_partition_is_unaffected_by_the_first
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(featured: false).where(position: { gte: 0 }).to_a
+    assert_equal [1, 2], results.map { |p| p['position'] }.sort
+    assert_equal 0, @store.scan_count
+  end
+
+  def test_range_without_any_equality_falls_back_to_a_scan_not_the_composite_index
+    # This fixture only has the composite [featured, position] index, no
+    # standalone index on position - a bare range with no equality column
+    # to pair with can use neither the plain range path (single-column
+    # only) nor the composite one (needs an equality prefix), so a scan is
+    # the correct, honest answer here, not a false "it found an index".
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(position: { gte: 3 }).to_a
+    assert_equal [3], results.map { |p| p['position'] }
+    assert_equal 1, @store.scan_count
+    assert_equal 0, @store.eq_range_hits, 'no equality column means no composite prefix to look up'
+  end
+
+  def test_equality_without_any_range_falls_back_to_a_scan_not_the_composite_index
+    # Same reasoning as above, mirrored: this fixture has no standalone
+    # index on featured either, only the composite - a bare equality with
+    # no range column to pair with can't use a composite index that
+    # requires ALL its columns pinned (see Store#lookup_by_index), so this
+    # is a scan too, not a spurious composite hit.
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(featured: true).to_a
+    assert_equal 3, results.size
+    assert_equal 1, @store.scan_count
+    assert_equal 0, @store.eq_range_hits
+  end
+
+  def test_reflects_a_reorder_through_the_underlying_model
+    post = EqRangeIndexedPost.where(featured: true).where(position: 1).first
+    post.class.store.increment_counter(post.class.table_name, post.id, 'position', 10)
+
+    @store.reset_counts!
+    results = EqRangeIndexedPost.where(featured: true).where(position: { lt: 3 }).to_a
+    assert_equal [2], results.map { |p| p['position'] }
+    assert_equal 0, @store.scan_count
+  end
+end