fix: address remaining PR review comments

Complete all remaining review feedback:

1. Restore handle_shift_tab() fallback behavior
   - Now handles non-list lines by removing indentation
   - Matches original implementation behavior
   - Provides consistent behavior for users

2. Fix handle_backspace() line deletion bug
   - Use atomic nvim_buf_set_lines() to avoid line number shifts
   - Prevents race condition when joining lines

3. Enhanced API documentation
   - Added detailed docstrings for get_next_marker()
   - Added detailed docstrings for get_previous_marker()
   - Clarified behavior for different list types
   - Improved parameter and return value descriptions

4. Clarified is_list_breaking_line() comment
   - Added comment explaining non-list content (headers, paragraphs)
   - Makes logic more explicit

All 169 tests passing. No lint errors.

Author: YousefHadder

lua/markdown-plus/list/handlers.lua

@@ -112,6 +112,18 @@ function M.handle_shift_tab()
   local list_info = parser.parse_list_line(current_line)
 
   if not list_info then
+    -- Not a list line: remove up to shiftwidth spaces from start
+    local cursor = utils.get_cursor()
+    local row, col = cursor[1], cursor[2]
+    local indent_size = vim.bo.shiftwidth or 2
+    local leading = current_line:match("^(%s*)")
+    local to_remove = math.min(#leading, indent_size)
+    if to_remove > 0 then
+      local new_line = current_line:sub(to_remove + 1)
+      utils.set_line(row, new_line)
+      local new_col = math.max(0, col - to_remove)
+      utils.set_cursor(row, new_col)
+    end
     return
   end
 
@@ -155,8 +167,7 @@ function M.handle_backspace()
       -- At start of line, join with previous line
       local prev_line = utils.get_line(row - 1)
       local joined_line = prev_line .. current_line
-      utils.set_line(row - 1, joined_line)
-      vim.api.nvim_buf_set_lines(0, row - 1, row, false, {})
+      vim.api.nvim_buf_set_lines(0, row - 2, row, false, { joined_line })
       utils.set_cursor(row - 1, #prev_line)
     end
     return

lua/markdown-plus/list/parser.lua

@@ -158,9 +158,11 @@ function M.next_letter(letter, is_upper)
   end
 end
 
----Get the next marker for a list item
----@param list_info table List information
----@return string Next marker
+---Get the next marker for a list item, incrementing numbers or letters as appropriate
+---For ordered lists: "1." -> "2.", for letters: "a." -> "b."
+---For unordered lists: returns same marker ("-", "+", "*")
+---@param list_info table Table containing list item information (type, marker, etc.)
+---@return string next_marker The next marker string for the list item (e.g., "2.", "b)", "-")
 function M.get_next_marker(list_info)
   if list_info.type == "ordered" then
     local current_num = tonumber(list_info.marker:match("(%d+)"))
@@ -187,9 +189,11 @@ function M.get_next_marker(list_info)
 end
 
 ---Get the previous/initial marker for inserting before current item
----@param list_info table Current list information
----@param row number Current row number
----@return string Previous marker
+---Checks if there's a previous list item at same indent and returns incremented marker,
+---otherwise returns initial marker ("1.", "a.", etc.)
+---@param list_info table Current list information (type, marker, indent, etc.)
+---@param row number Current row number (1-indexed)
+---@return string previous_marker The marker to use for item inserted above (e.g., "1.", "a)", "-")
 function M.get_previous_marker(list_info, row)
   local is_ordered = list_info.type == "ordered" or list_info.type == "ordered_paren"
   local is_letter_lower = list_info.type == "letter_lower" or list_info.type == "letter_lower_paren"

lua/markdown-plus/list/renumber.lua

@@ -29,6 +29,8 @@ function M.is_list_breaking_line(line)
   if parser.parse_list_line(line) then
     return false
   end
+
+  -- Any non-list content (headers, paragraphs, etc.) breaks list continuity
   return true
 end