feat(ui/output): add max_messages option to limit rendered messages (#354)

* feat(ui/output): add max_messages option to limit rendered messages

Add support for ui.output.max_messages to cap how many messages are kept
rendered in the output buffer. When the configured limit is exceeded the
oldest messages for the active session are evicted and a hidden-messages
notice is inserted/updated to indicate how many older messages are
not displayed.

This should fix #320

* feat(output): add toggle for maximum rendered messages

Add a workflow action and command to toggle ui.output.max_messages between a finite
number and nil (no limit). Wire the action into the API, keymaps (<leader>otm),
types, and UI so users can enable/disable the message limit from the output
notice or via command. The toggle notifies the user of the current state. Also
ensure render_output returns its promise/value so callers can await rendering when
requested.

* fix: re-render ui when toggling max messages

Author: sudo-tee

README.md

@@ -243,6 +243,7 @@ require('opencode').setup({
         markdown_debounce_ms = 250, -- Debounce time for markdown rendering on new data (default: 250ms)
         on_data_rendered = nil, -- Called when new data is rendered; set to false to disable default RenderMarkdown/Markview behavior
       },
+      max_messages = nil, -- Max number of messages to keep in the output buffer; older messages will be removed as new ones arrive (default: nil, which means no limit)
     },
     input = {
       min_height = 0.10, -- min height of prompt input as percentage of window height

lua/opencode/api.lua

@@ -89,6 +89,7 @@ local action_groups = {
     debug_session = workflow.debug_session,
     toggle_tool_output = workflow.toggle_tool_output,
     toggle_reasoning_output = workflow.toggle_reasoning_output,
+    toggle_max_messages = workflow.toggle_max_messages,
     submit_input_prompt = workflow.submit_input_prompt,
     run = workflow.run,
     run_new_session = workflow.run_new_session,

lua/opencode/commands/handlers/workflow.lua

@@ -283,6 +283,23 @@ function M.actions.toggle_reasoning_output()
   ui.render_output()
 end
 
+local original_max_messages = config.ui.output.max_messages
+function M.actions.toggle_max_messages()
+  local current = config.ui.output.max_messages
+  local next_val
+  if type(current) == 'number' and current > 0 then
+    next_val = nil
+  else
+    next_val = original_max_messages or 20
+  end
+
+  local action_text = next_val == nil and 'Disabling' or 'Enabling'
+  local val_text = next_val == nil and 'none' or tostring(next_val)
+  vim.notify(action_text .. ' message limit to ' .. val_text, vim.log.levels.INFO)
+  config.values.ui.output.max_messages = next_val
+  ui.render_output()
+end
+
 M.actions.review = Promise.async(function(args)
   local new_session = core.create_new_session('Code review checklist for diffs and PRs'):await()
   if not new_session then
@@ -453,6 +470,10 @@ M.command_defs = {
     desc = 'Toggle reasoning output visibility in the output window',
     execute = M.actions.toggle_reasoning_output,
   },
+  toggle_max_messages = {
+    desc = 'Toggle maximum number of rendered messages',
+    execute = M.actions.toggle_max_messages,
+  },
   paste_image = {
     desc = 'Paste image from clipboard and add to context',
     execute = M.actions.paste_image,

lua/opencode/config.lua

@@ -56,7 +56,9 @@ M.defaults = {
       ['<leader>ox'] =  { 'swap_position',                                     desc = 'Swap window position' },
       ['<leader>otr'] = { 'toggle_reasoning_output',                           desc = 'Toggle reasoning output' },
       ['<leader>ott'] = { 'toggle_tool_output',                                desc = 'Toggle tool output' },
+      ['<leader>otm'] = { 'toggle_max_messages',                               desc = 'Toggle max messages' },
       ['<leader>o/'] =  { 'quick_chat',                   mode = { 'n', 'x' }, desc = 'Quick chat with current context' },
+
     },
     output_window = {
       ['<esc>'] =       { 'close',                                             desc = 'Close Opencode windows' },
@@ -155,6 +157,7 @@ M.defaults = {
         show_output = true,
         show_reasoning_output = true,
       },
+      max_messages = nil,
       always_scroll_to_bottom = false,
     },
     questions = {

lua/opencode/types.lua

@@ -244,6 +244,7 @@
 ---@class OpencodeUIOutputConfig
 ---@field tools { show_output: boolean, show_reasoning_output: boolean }
 ---@field rendering OpencodeUIOutputRenderingConfig
+---@field max_messages integer|nil
 ---@field always_scroll_to_bottom boolean
 ---@field filetype string
 ---@field compact_assistant_headers boolean | 'minimal' | 'hidden' | 'full'
@@ -498,7 +499,7 @@
 
 ---@class OutputAction
 ---@field text string Action text
----@field type 'diff_revert_all'|'diff_revert_selected_file'|'diff_open'|'diff_restore_snapshot_file'|'diff_restore_snapshot_all'|'select_child_session' Type of action
+---@field type 'diff_revert_all'|'diff_revert_selected_file'|'diff_open'|'diff_restore_snapshot_file'|'diff_restore_snapshot_all'|'select_child_session'|'toggle_max_messages'
 ---@field args? string[] Optional arguments for the command
 ---@field key string keybinding for the action
 ---@field display_line number Line number to display the action

lua/opencode/ui/formatter.lua

@@ -99,6 +99,26 @@ function M._format_revert_message(session_data, start_idx)
   return output
 end
 
+---@param hidden_count integer
+---@return Output
+function M._format_hidden_messages_notice(hidden_count)
+  local output = Output.new()
+  local message_text = hidden_count == 1 and 'message is' or 'messages are'
+
+  output:add_line(string.format('> %d older %s not displayed.', hidden_count, message_text))
+  output:add_action({
+    text = 'Show [A]ll messages',
+    type = 'toggle_max_messages',
+    args = {},
+    key = 'A',
+    display_line = output:get_line_count() - 1,
+    range = { from = output:get_line_count() - 1, to = output:get_line_count() - 1 },
+  })
+  output:add_empty_line()
+
+  return output
+end
+
 ---@param output Output
 ---@param text string
 ---@param action_type string
@@ -167,6 +187,10 @@ function M.format_message_header(message, previous_message)
     return output
   end
 
+  if message.info and message.info.id == '__opencode_hidden_messages_notice__' then
+    return output
+  end
+
   local role = message.info.role or 'unknown'
   local icon = message.info.role == 'user' and icons.get('header_user') or icons.get('header_assistant')
 
@@ -674,6 +698,12 @@ function M.format_part(part, message, is_last_part, get_child_parts)
         output = M._format_revert_message(state.messages or {}, revert_index)
         content_added = output:get_line_count() > 0
       end
+    elseif part.type == 'hidden-messages-display' then
+      local hidden_count = part.state and part.state.hidden_count
+      if type(hidden_count) == 'number' and hidden_count > 0 then
+        output = M._format_hidden_messages_notice(hidden_count)
+        content_added = output:get_line_count() > 0
+      end
     end
   end