feat: text objects and motions for the pending buffer

Problem: the pending buffer has action-button mappings but no Vim
grammar. You cannot dat to delete a task, cit to change a description,
or ]] to jump to the next category header.

Solution: add textobj.lua with at/it (a task / inner task), aC/iC
(a category / inner category), ]]/[[ (next/prev header), and ]t/[t
(next/prev task). All text objects work in operator-pending and visual
modes; motions work in normal, visual, and operator-pending. Mappings
are configurable via the keymaps table and exposed as <Plug> mappings.

spec/textobj_spec.lua

@@ -0,0 +1,193 @@
+require('spec.helpers')
+
+local config = require('pending.config')
+
+describe('textobj', function()
+  local textobj = require('pending.textobj')
+
+  before_each(function()
+    vim.g.pending = nil
+    config.reset()
+  end)
+
+  after_each(function()
+    vim.g.pending = nil
+    config.reset()
+  end)
+
+  describe('inner_task_range', function()
+    it('returns description range for task with id prefix', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy groceries')
+      assert.are.equal(11, s)
+      assert.are.equal(23, e)
+    end)
+
+    it('returns description range for task without id prefix', function()
+      local s, e = textobj.inner_task_range('- [ ] Buy groceries')
+      assert.are.equal(7, s)
+      assert.are.equal(19, e)
+    end)
+
+    it('excludes trailing due: token', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy groceries due:2026-03-15')
+      assert.are.equal(11, s)
+      assert.are.equal(23, e)
+    end)
+
+    it('excludes trailing cat: token', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy groceries cat:Errands')
+      assert.are.equal(11, s)
+      assert.are.equal(23, e)
+    end)
+
+    it('excludes trailing rec: token', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Take out trash rec:weekly')
+      assert.are.equal(11, s)
+      assert.are.equal(25, e)
+    end)
+
+    it('excludes multiple trailing metadata tokens', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy milk due:2026-03-15 cat:Errands rec:weekly')
+      assert.are.equal(11, s)
+      assert.are.equal(18, e)
+    end)
+
+    it('handles priority checkbox', function()
+      local s, e = textobj.inner_task_range('/1/- [!] Important task')
+      assert.are.equal(11, s)
+      assert.are.equal(24, e)
+    end)
+
+    it('handles done checkbox', function()
+      local s, e = textobj.inner_task_range('/1/- [x] Finished task')
+      assert.are.equal(11, s)
+      assert.are.equal(23, e)
+    end)
+
+    it('handles multi-digit task ids', function()
+      local s, e = textobj.inner_task_range('/123/- [ ] Some task')
+      assert.are.equal(13, s)
+      assert.are.equal(21, e)
+    end)
+
+    it('does not strip non-metadata tokens', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy groceries for dinner')
+      assert.are.equal(11, s)
+      assert.are.equal(34, e)
+    end)
+
+    it('stops stripping at first non-metadata token from right', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy groceries for dinner due:2026-03-15')
+      assert.are.equal(11, s)
+      assert.are.equal(34, e)
+    end)
+
+    it('respects custom date_syntax', function()
+      vim.g.pending = { date_syntax = 'by' }
+      config.reset()
+      local s, e = textobj.inner_task_range('/1/- [ ] Buy groceries by:2026-03-15')
+      assert.are.equal(11, s)
+      assert.are.equal(23, e)
+    end)
+
+    it('respects custom recur_syntax', function()
+      vim.g.pending = { recur_syntax = 'repeat' }
+      config.reset()
+      local s, e = textobj.inner_task_range('/1/- [ ] Take trash repeat:weekly')
+      assert.are.equal(11, s)
+      assert.are.equal(20, e)
+    end)
+
+    it('handles task with only metadata after description', function()
+      local s, e = textobj.inner_task_range('/1/- [ ] X due:tomorrow')
+      assert.are.equal(11, s)
+      assert.are.equal(11, e)
+    end)
+  end)
+
+  describe('category_bounds', function()
+    it('returns header and last row for single category', function()
+      ---@type pending.LineMeta[]
+      local meta = {
+        { type = 'header', category = 'Work' },
+        { type = 'task', id = 1 },
+        { type = 'task', id = 2 },
+      }
+      local h, l = textobj.category_bounds(2, meta)
+      assert.are.equal(1, h)
+      assert.are.equal(3, l)
+    end)
+
+    it('returns bounds for first category with trailing blank', function()
+      ---@type pending.LineMeta[]
+      local meta = {
+        { type = 'header', category = 'Work' },
+        { type = 'task', id = 1 },
+        { type = 'blank' },
+        { type = 'header', category = 'Personal' },
+        { type = 'task', id = 2 },
+      }
+      local h, l = textobj.category_bounds(2, meta)
+      assert.are.equal(1, h)
+      assert.are.equal(2, l)
+    end)
+
+    it('returns bounds for second category', function()
+      ---@type pending.LineMeta[]
+      local meta = {
+        { type = 'header', category = 'Work' },
+        { type = 'task', id = 1 },
+        { type = 'blank' },
+        { type = 'header', category = 'Personal' },
+        { type = 'task', id = 2 },
+        { type = 'task', id = 3 },
+      }
+      local h, l = textobj.category_bounds(5, meta)
+      assert.are.equal(4, h)
+      assert.are.equal(6, l)
+    end)
+
+    it('returns bounds when cursor is on header', function()
+      ---@type pending.LineMeta[]
+      local meta = {
+        { type = 'header', category = 'Work' },
+        { type = 'task', id = 1 },
+      }
+      local h, l = textobj.category_bounds(1, meta)
+      assert.are.equal(1, h)
+      assert.are.equal(2, l)
+    end)
+
+    it('returns nil for blank line with no preceding header', function()
+      ---@type pending.LineMeta[]
+      local meta = {
+        { type = 'blank' },
+        { type = 'header', category = 'Work' },
+        { type = 'task', id = 1 },
+      }
+      local h, l = textobj.category_bounds(1, meta)
+      assert.is_nil(h)
+      assert.is_nil(l)
+    end)
+
+    it('returns nil for empty meta', function()
+      local h, l = textobj.category_bounds(1, {})
+      assert.is_nil(h)
+      assert.is_nil(l)
+    end)
+
+    it('includes blank between header and next header in bounds', function()
+      ---@type pending.LineMeta[]
+      local meta = {
+        { type = 'header', category = 'Work' },
+        { type = 'task', id = 1 },
+        { type = 'blank' },
+        { type = 'header', category = 'Home' },
+        { type = 'task', id = 2 },
+      }
+      local h, l = textobj.category_bounds(1, meta)
+      assert.are.equal(1, h)
+      assert.are.equal(3, l)
+    end)
+  end)
+end)