assert(index, 'file missing from manifest')
  table.remove(File_navigation.all_candidates, index)
  table.insert(File_navigation.all_candidates, 1, s)

  Text.populate_link_offsets(State, line_index)

--?   print('down', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  assert(State.cursor1.pos)

  assert(State.lines[State.cursor1.line].mode == 'text', 'line is not text')
  assert(State.cursor1.pos, 'cursor has no pos')

--?   print('down', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)

      assert(State.lines[top2.line-1].mode == 'drawing')

  assert(index)

  assert(index, 'file missing from manifest')

  assert(Directory)

  assert(Directory, 'no directory to browse notes in')

      print_and_log('refresh_pane_height: '..line.mode)
      assert(false)

      assert(false, ('unknown line mode %s'):format(line.mode))

    print_and_log('run.draw: '..Display_settings.mode)
    assert(false)

    assert(false, ('pensieve is in an unknown mode %s'):format(Display_settings.mode))

  assert(Cursor_pane.col)
  assert(Cursor_pane.row)

  assert(Cursor_pane.col, 'no current column')
  assert(Cursor_pane.row, 'no current row')

    assert(pane.top)

    assert(pane.top, "pane has no top coordinate; there's likely a problem in plan_draw")

  assert(pane.title)

  assert(pane.title, 'pane has no title')

  assert(Directory_error == nil)  -- this will go into an infinite loop if handle_error ever tries to save settings

  -- avoid an infinite loop if handle_error ever tries to save settings
  assert(Directory_error == nil,
        "tried to save settings when we couldn't determine the directory to browse notes in")

  assert(status)

  assert(status, 'failed to write settings')

    print_and_log('run.mouse_press: '..Display_settings.mode)
    assert(false)

    assert(false, ('pensieve is in an unknown mode %s'):format(Display_settings.mode))

    print_and_log('run.text_input: '..Display_settings.mode)
    assert(false)

    assert(false, ('pensieve is in an unknown mode %s'):format(Display_settings.mode))

            assert(pane.cursor_y == nil)

            assert(pane.cursor_y == nil, 'cursor x is not set but y is set')

    print_and_log('run.keychord_press: '..Display_settings.mode)
    assert(false)

    assert(false, ('pensieve is in an unknown mode %s'):format(Display_settings.mode))

  else
    assert(dir == 'down')

  elseif dir == 'down' then

      assert(App.screen.height - (cursor_sy-Display_settings.y) > 1.5*Line_height)

      assert(App.screen.height - (cursor_sy-Display_settings.y) > 1.5*Line_height, 'ugh, ancient bug is back: panning the viewport when cursor falls off')
    else
      assert(false, ('unknown dir %s'):format(dir))

  assert(y >= 0)

  assert(y >= 0, 'something is at negative y on the surface')

        assert(nlines >= 0 and nlines < #pane.line_cache[i].screen_line_starting_pos)

        assert(nlines >= 0 and nlines < #pane.line_cache[i].screen_line_starting_pos, 'error in mapping y coordinate to schema-1')

  assert(edit_count <= 1)

  assert(edit_count <= 1, 'multiple panes were editable')

      assert(not err)

      assert(not err, 'failed to save recent')

      print_and_log('load_drawing: '..shape.mode)

      print_and_log('store_drawing: '..shape.mode)

  assert(status)

  assert(status, 'failed to create directory for links')

      print_and_log('load_drawing_from_array: '..shape.mode)

  if #State.lines ~= #State.line_cache then
    log(2, os.date('%Y/%m/%d/%H-%M-%S')..(' line_cache is out of date; %d when it should be %d'):format(#State.line_cache, #State.lines))
    assert(false)
  end

  assert(#State.lines == #State.line_cache, ('line_cache is out of date; %d elements when it should be %d'):format(#State.line_cache, #State.lines))

  assert(#State.lines == #State.line_cache, ('line_cache is out of date; %d elements when it should be %d'):format(#State.line_cache, #State.lines))
  assert(Text.le1(State.screen_top1, State.cursor1), ('screen_top (line=%d,pos=%d) is below cursor (line=%d,pos=%d)'):format(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos))

    if State.editable and geom.on_shape(mx,my, line, shape) then

  if line_cache.starty == nil then
    -- some event cleared starty just this frame
    -- draw in this frame will soon set starty
    -- just skip this frame
    return
  end

  assert(drawing.mode == 'drawing', 'Drawing.update: line is not a drawing')

            assert(pane.cursor_y)

            assert(pane.cursor_y, 'cursor fell off viewport')

  assert(not pane.editable)

  assert(not pane.editable, 'pane already editable')

  assert(Cursor_pane.col >= 1)

  assert(Cursor_pane.col >= 1, 'no current pane')

  assert(pane)
  assert(pane.editable)

  assert(pane, 'no current pane')
  assert(pane.editable, 'current pane not editable')

    assert(Display_settings.search_all_query:sub(#Display_settings.search_all_query) == '"')

    assert(Display_settings.search_all_query:sub(#Display_settings.search_all_query) == '"', 'you can search for strings in quotes, but only one of them by itself')

    assert(arr)
    assert(type(arr) == 'table')

    assert(arr, 'found no link')
    assert(type(arr) == 'table', 'links not arranged in a table')

    assert(pos)

    assert(pos, "couldn't find link to remove in links table")

    assert(Links[src][rel] == target)

    assert(Links[src][rel] == target, 'link at this rel is not the target; giving up')

    assert(Cursor_pane.row == 1)

    assert(Cursor_pane.row == 1, "couldn't set current pane after unrolling")

    assert(Cursor_pane.row == 1)

    assert(Cursor_pane.row == 1, "couldn't repurpose column for neighbors")

    assert(not delete_cursor_column)

    assert(not delete_cursor_column, "failed to delete note's column")

  assert(status)

  assert(status, "failed to create directory for note")