feat: add markdown detail buffer for task notes

Problem: tasks only have a one-line description. There is no way to
attach extended notes, checklists, or context to a task.

Solution: add `ge` keymap to open a `pending://task/<id>` markdown
buffer that replaces the task list in the same split. The buffer shows
a read-only metadata header (status, priority, category, due,
recurrence) rendered via extmarks, a `---` separator, and editable
notes below. `:w` saves notes to a new top-level `notes` field on the
task stored in the single `tasks.json`. `q` returns to the task list.

doc/pending.txt

@@ -348,6 +348,7 @@ Default buffer-local keys: ~
     `gw`          Toggle work-in-progress status (`wip`)
     `gb`          Toggle blocked status (`blocked`)
     `g/`          Toggle cancelled status (`cancelled`)
+    `ge`          Open markdown detail buffer for task notes (`edit_notes`)
     `gf`          Prompt for filter predicates (`filter`)
     `<Tab>`       Switch between category / queue view (`view`)
     `gz`          Undo the last `:w` save (`undo`)
@@ -487,6 +488,12 @@ old keys to `false`: >lua
     Decrement the priority level for the task under the cursor, clamped
     at 0. Default key: `<C-x>`.
 
+                                               *<Plug>(pending-edit-notes)*
+<Plug>(pending-edit-notes)
+    Open the markdown detail buffer for the task under the cursor.
+    Shows a read-only metadata header and editable notes below a `---`
+    separator. Press `q` to return to the task list. Default key: `ge`.
+
                                                    *<Plug>(pending-open-line)*
 <Plug>(pending-open-line)
     Insert a correctly-formatted blank task line below the cursor.
@@ -557,6 +564,29 @@ Queue view: ~                                             *pending-view-queue*
     virtual text so tasks remain identifiable across categories. The
     buffer is named `pending://queue`.
 
+==============================================================================
+DETAIL BUFFER                                           *pending-detail-buffer*
+
+Press `ge` (or `keymaps.edit_notes`) on a task to open a markdown detail
+buffer named `pending://task/<id>`. The buffer replaces the task list in
+the same split.
+
+Layout: ~
+
+    Line 1:     `# <description>` (task description as heading)
+    Lines 2-3:  Read-only metadata (status, priority, category, due,
+                recurrence) rendered as virtual text overlays
+    Line 4:     `---` separator
+    Line 5+:    Free-form markdown notes (editable)
+
+The metadata header is not editable — it is rendered via extmarks on
+empty buffer lines. To change metadata, return to the task list and use
+the normal keymaps or `:Pending edit`.
+
+Write (`:w`) saves the notes content (everything below the `---`
+separator) to the `notes` field in the task store. Press `q` to return
+to the task list.
+
 ==============================================================================
 FILTERS                                                       *pending-filters*
 
@@ -789,6 +819,7 @@ loads: >lua
         wip = 'gw',
         blocked = 'gb',
         cancelled = 'g/',
+        edit_notes = 'ge',
       },
       sync = {
         gcal = {},
@@ -1651,6 +1682,7 @@ Task fields: ~
     {entry}       (string)  ISO 8601 UTC timestamp of creation.
     {modified}    (string)  ISO 8601 UTC timestamp of last modification.
     {end}         (string)  ISO 8601 UTC timestamp of completion or deletion.
+    {notes}       (string)  Free-form markdown notes (from detail buffer).
     {order}       (integer) Relative ordering within a category.
 
 Any field not in the list above is preserved in `_extra` and written back on

lua/pending/buffer.lua

@@ -584,6 +584,7 @@ local function setup_highlights()
   vim.api.nvim_set_hl(0, 'PendingFilter', { link = 'DiagnosticWarn', default = true })
   vim.api.nvim_set_hl(0, 'PendingForge', { link = 'DiagnosticInfo', default = true })
   vim.api.nvim_set_hl(0, 'PendingForgeClosed', { link = 'Comment', default = true })
+  vim.api.nvim_set_hl(0, 'PendingDetailMeta', { link = 'Comment', default = true })
 end
 
 ---@return string
@@ -805,4 +806,213 @@ function M.open()
   return task_bufnr
 end
 
+local ns_detail = vim.api.nvim_create_namespace('pending_detail')
+local DETAIL_SEPARATOR = '---'
+
+---@type integer?
+local _detail_bufnr = nil
+---@type integer?
+local _detail_task_id = nil
+
+---@return integer?
+function M.detail_bufnr()
+  return _detail_bufnr
+end
+
+---@return integer?
+function M.detail_task_id()
+  return _detail_task_id
+end
+
+---@param bufnr integer
+---@param task pending.Task
+---@return nil
+local function apply_detail_extmarks(bufnr, task)
+  vim.api.nvim_buf_clear_namespace(bufnr, ns_detail, 0, -1)
+  local icons = config.get().icons
+  local parts = {}
+  local status_label = task.status or 'pending'
+  local icon_char = icons[status_label] or icons.pending
+  table.insert(parts, { 'Status: [' .. icon_char .. '] ' .. status_label, 'PendingDetailMeta' })
+  if task.priority and task.priority > 0 then
+    table.insert(parts, { '  ', 'Normal' })
+    table.insert(
+      parts,
+      { 'Priority: ' .. string.rep(icons.priority, task.priority), 'PendingDetailMeta' }
+    )
+  end
+  local line2 = {}
+  if task.category then
+    table.insert(line2, { 'Category: ' .. task.category, 'PendingDetailMeta' })
+  end
+  if task.due then
+    if #line2 > 0 then
+      table.insert(line2, { '  ', 'Normal' })
+    end
+    local due_label = task.due
+    local y, mo, d = task.due:match('^(%d%d%d%d)%-(%d%d)%-(%d%d)')
+    if y then
+      local t = os.time({
+        year = tonumber(y) --[[@as integer]],
+        month = tonumber(mo) --[[@as integer]],
+        day = tonumber(d) --[[@as integer]],
+      })
+      due_label = os.date(config.get().date_format, t) --[[@as string]]
+    end
+    table.insert(line2, { 'Due: ' .. due_label, 'PendingDetailMeta' })
+  end
+  if task.recur then
+    if #line2 > 0 then
+      table.insert(line2, { '  ', 'Normal' })
+    end
+    table.insert(line2, { 'Recur: ' .. task.recur, 'PendingDetailMeta' })
+  end
+  if #parts > 0 then
+    vim.api.nvim_buf_set_extmark(bufnr, ns_detail, 1, 0, {
+      virt_text = parts,
+      virt_text_pos = 'overlay',
+    })
+  end
+  if #line2 > 0 then
+    vim.api.nvim_buf_set_extmark(bufnr, ns_detail, 2, 0, {
+      virt_text = line2,
+      virt_text_pos = 'overlay',
+    })
+  end
+end
+
+---@param task_id integer
+---@return integer? bufnr
+function M.open_detail(task_id)
+  if not _store then
+    return nil
+  end
+  if _detail_bufnr and vim.api.nvim_buf_is_valid(_detail_bufnr) then
+    if _detail_task_id == task_id then
+      return _detail_bufnr
+    end
+    vim.api.nvim_buf_delete(_detail_bufnr, { force = true })
+    _detail_bufnr = nil
+    _detail_task_id = nil
+  end
+  local task = _store:get(task_id)
+  if not task then
+    log.warn('task not found: ' .. task_id)
+    return nil
+  end
+
+  setup_highlights()
+
+  local bufnr = vim.api.nvim_create_buf(true, false)
+  vim.api.nvim_buf_set_name(bufnr, 'pending://task/' .. task_id)
+  vim.bo[bufnr].buftype = 'acwrite'
+  vim.bo[bufnr].filetype = 'markdown'
+  vim.bo[bufnr].swapfile = false
+
+  local lines = {
+    '# ' .. task.description,
+    '',
+    '',
+    DETAIL_SEPARATOR,
+  }
+  local notes = task.notes or ''
+  if notes ~= '' then
+    for note_line in (notes .. '\n'):gmatch('(.-)\n') do
+      table.insert(lines, note_line)
+    end
+  else
+    table.insert(lines, '')
+  end
+
+  vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+  vim.bo[bufnr].modified = false
+
+  apply_detail_extmarks(bufnr, task)
+
+  local winid = task_winid
+  if winid and vim.api.nvim_win_is_valid(winid) then
+    vim.api.nvim_win_set_buf(winid, bufnr)
+  end
+
+  vim.wo[winid].conceallevel = 0
+  vim.wo[winid].foldmethod = 'manual'
+  vim.wo[winid].foldenable = false
+
+  _detail_bufnr = bufnr
+  _detail_task_id = task_id
+
+  local separator_row = 3
+  local cursor_row = separator_row + 2
+  local total = vim.api.nvim_buf_line_count(bufnr)
+  if cursor_row > total then
+    cursor_row = total
+  end
+  pcall(vim.api.nvim_win_set_cursor, winid, { cursor_row, 0 })
+
+  return bufnr
+end
+
+---@return nil
+function M.close_detail()
+  if _detail_bufnr and vim.api.nvim_buf_is_valid(_detail_bufnr) then
+    vim.api.nvim_buf_delete(_detail_bufnr, { force = true })
+  end
+  _detail_bufnr = nil
+  _detail_task_id = nil
+
+  if task_winid and vim.api.nvim_win_is_valid(task_winid) then
+    if task_bufnr and vim.api.nvim_buf_is_valid(task_bufnr) then
+      vim.api.nvim_win_set_buf(task_winid, task_bufnr)
+      set_win_options(task_winid)
+      M.render(task_bufnr)
+    end
+  end
+end
+
+---@return nil
+function M.save_detail()
+  if not _detail_bufnr or not _detail_task_id or not _store then
+    return
+  end
+  local task = _store:get(_detail_task_id)
+  if not task then
+    log.warn('task was deleted')
+    M.close_detail()
+    return
+  end
+
+  local lines = vim.api.nvim_buf_get_lines(_detail_bufnr, 0, -1, false)
+
+  local sep_row = nil
+  for i, line in ipairs(lines) do
+    if line == DETAIL_SEPARATOR then
+      sep_row = i
+      break
+    end
+  end
+
+  local notes_text = ''
+  if sep_row and sep_row < #lines then
+    local note_lines = {}
+    for i = sep_row + 1, #lines do
+      table.insert(note_lines, lines[i])
+    end
+    notes_text = table.concat(note_lines, '\n')
+    notes_text = notes_text:gsub('%s+$', '')
+  end
+
+  if notes_text == '' then
+    _store:update(_detail_task_id, { notes = vim.NIL })
+  else
+    _store:update(_detail_task_id, { notes = notes_text })
+  end
+  _store:save()
+
+  vim.bo[_detail_bufnr].modified = false
+  local updated = _store:get(_detail_task_id)
+  if updated then
+    apply_detail_extmarks(_detail_bufnr, updated)
+  end
+end
+
 return M

lua/pending/config.lua

@@ -82,6 +82,7 @@
 ---@field priority_up_visual? string|false
 ---@field priority_down_visual? string|false
 ---@field cancelled? string|false
+---@field edit_notes? string|false
 
 ---@class pending.CategoryViewConfig
 ---@field order? string[]
@@ -163,6 +164,7 @@ local defaults = {
     wip = 'gw',
     blocked = 'gb',
     cancelled = 'g/',
+    edit_notes = 'ge',
     priority_up = '<C-a>',
     priority_down = '<C-x>',
     priority_up_visual = 'g<C-a>',

lua/pending/init.lua

@@ -401,6 +401,9 @@ function M._setup_buf_mappings(bufnr)
     open_line_above = function()
       buffer.open_line(true)
     end,
+    edit_notes = function()
+      M.open_detail()
+    end,
   }
 
   for name, fn in pairs(actions) do
@@ -888,6 +891,46 @@ function M.toggle_status(target_status)
   end
 end
 
+---@return nil
+function M.open_detail()
+  local bufnr = buffer.bufnr()
+  if not bufnr then
+    return
+  end
+  if not require_saved() then
+    return
+  end
+  local row = vim.api.nvim_win_get_cursor(0)[1]
+  local meta = buffer.meta()
+  if not meta[row] or meta[row].type ~= 'task' then
+    return
+  end
+  local id = meta[row].id
+  if not id then
+    return
+  end
+
+  local detail_bufnr = buffer.open_detail(id)
+  if not detail_bufnr then
+    return
+  end
+
+  local group = vim.api.nvim_create_augroup('PendingDetail', { clear = true })
+  vim.api.nvim_create_autocmd('BufWriteCmd', {
+    group = group,
+    buffer = detail_bufnr,
+    callback = function()
+      buffer.save_detail()
+    end,
+  })
+
+  local km = require('pending.config').get().keymaps
+  vim.keymap.set('n', km.close or 'q', function()
+    vim.api.nvim_del_augroup_by_name('PendingDetail')
+    buffer.close_detail()
+  end, { buffer = detail_bufnr })
+end
+
 ---@param direction 'up'|'down'
 ---@return nil
 function M.move_task(direction)

lua/pending/store.lua

@@ -24,6 +24,7 @@ local config = require('pending.config')
 ---@field entry string
 ---@field modified string
 ---@field end? string
+---@field notes? string
 ---@field order integer
 ---@field _extra? pending.TaskExtra
 
@@ -93,6 +94,7 @@ local known_fields = {
   entry = true,
   modified = true,
   ['end'] = true,
+  notes = true,
   order = true,
 }
 
@@ -124,6 +126,9 @@ local function task_to_table(task)
   if task['end'] then
     t['end'] = task['end']
   end
+  if task.notes then
+    t.notes = task.notes
+  end
   if task.order and task.order ~= 0 then
     t.order = task.order
   end
@@ -150,6 +155,7 @@ local function table_to_task(t)
     entry = t.entry,
     modified = t.modified,
     ['end'] = t['end'],
+    notes = t.notes,
     order = t.order or 0,
     _extra = {},
   }

lua/pending/views.lua

@@ -341,6 +341,7 @@ function M.priority_view(tasks)
       forge_ref = task._extra and task._extra._forge_ref or nil,
       forge_cache = task._extra and task._extra._forge_cache or nil,
       forge_spans = compute_forge_spans(task, prefix_len),
+      has_notes = task.notes ~= nil and task.notes ~= '',
     })
   end
 

plugin/pending.lua

@@ -407,6 +407,10 @@ vim.keymap.set('n', '<Plug>(pending-cancelled)', function()
   require('pending').toggle_status('cancelled')
 end)
 
+vim.keymap.set('n', '<Plug>(pending-edit-notes)', function()
+  require('pending').open_detail()
+end)
+
 vim.keymap.set('n', '<Plug>(pending-priority-up)', function()
   require('pending').increment_priority()
 end)