feat(views): add hide_done_categories config option (#153)

Problem: Categories where every task is done still render in the buffer,
cluttering the view when entire categories are finished.

Solution: Add `view.category.hide_done_categories` (boolean, default
false). When enabled, `category_view()` skips categories whose tasks are
all done/deleted, returns their IDs as `done_cat_hidden_ids`, and
`_on_write` merges those IDs into `hidden_ids` passed to `diff.apply()`
so hidden tasks are not mistakenly deleted on `:w`.

lua/pending/buffer.lua

@@ -27,6 +27,8 @@ local _filter_predicates = {}
 ---@type table<integer, true>
 local _hidden_ids = {}
 ---@type table<integer, true>
+local _done_cat_hidden_ids = {}
+---@type table<integer, true>
 local _dirty_rows = {}
 ---@type boolean
 local _on_bytes_active = false
@@ -74,6 +76,11 @@ function M.hidden_ids()
   return _hidden_ids
 end
 
+---@return table<integer, true>
+function M.done_cat_hidden_ids()
+  return _done_cat_hidden_ids
+end
+
 ---@param predicates string[]
 ---@param hidden table<integer, true>
 ---@return nil
@@ -694,10 +701,13 @@ function M.render(bufnr)
   end
 
   local lines, line_meta
+  _done_cat_hidden_ids = {}
   if current_view == 'priority' then
     lines, line_meta = views.priority_view(tasks)
   else
-    lines, line_meta = views.category_view(tasks)
+    local done_cat_hidden
+    lines, line_meta, done_cat_hidden = views.category_view(tasks)
+    _done_cat_hidden_ids = done_cat_hidden
   end
 
   if #lines == 0 and #_filter_predicates == 0 then

lua/pending/config.lua

@@ -84,6 +84,7 @@
 ---@class pending.CategoryViewConfig
 ---@field order? string[]
 ---@field folding? boolean|pending.FoldingConfig
+---@field hide_done_categories? boolean
 
 ---@class pending.QueueViewConfig
 
@@ -130,6 +131,7 @@ local defaults = {
     category = {
       order = {},
       folding = true,
+      hide_done_categories = false,
     },
     queue = {},
   },

lua/pending/init.lua

@@ -509,6 +509,9 @@ function M._on_write(bufnr)
   if #stack > UNDO_MAX then
     table.remove(stack, 1)
   end
+  for id in pairs(buffer.done_cat_hidden_ids()) do
+    hidden[id] = true
+  end
   local new_refs = diff.apply(lines, s, hidden)
   M._recompute_counts()
   buffer.render(bufnr)

lua/pending/views.lua

@@ -138,6 +138,7 @@ end
 ---@param tasks pending.Task[]
 ---@return string[] lines
 ---@return pending.LineMeta[] meta
+---@return table<integer, true> done_cat_hidden_ids
 function M.category_view(tasks)
   local by_cat = {}
   local cat_order = {}
@@ -177,6 +178,9 @@ function M.category_view(tasks)
     cat_order = ordered
   end
 
+  local hide_done = config.get().view.category.hide_done_categories
+  local done_cat_hidden = {} ---@type table<integer, true>
+
   for _, cat in ipairs(cat_order) do
     sort_tasks(by_cat[cat])
     sort_tasks(done_by_cat[cat])
@@ -184,12 +188,21 @@ function M.category_view(tasks)
 
   local lines = {}
   local meta = {}
+  local rendered = 0
 
-  for i, cat in ipairs(cat_order) do
-    if i > 1 then
+  for _, cat in ipairs(cat_order) do
+    if hide_done and #by_cat[cat] == 0 and #done_by_cat[cat] > 0 then
+      for _, t in ipairs(done_by_cat[cat]) do
+        done_cat_hidden[t.id] = true
+      end
+      goto next_cat
+    end
+
+    if rendered > 0 then
       table.insert(lines, '')
       table.insert(meta, { type = 'blank' })
     end
+    rendered = rendered + 1
     table.insert(lines, '# ' .. cat)
     table.insert(meta, { type = 'header', category = cat })
 
@@ -220,9 +233,11 @@ function M.category_view(tasks)
         forge_spans = compute_forge_spans(task, prefix_len),
       })
     end
+
+    ::next_cat::
   end
 
-  return lines, meta
+  return lines, meta, done_cat_hidden
 end
 
 ---@param tasks pending.Task[]