diff --git a/README.md b/README.md
index 41cce54d..02f33861 100644
--- a/README.md
+++ b/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
diff --git a/lua/opencode/api.lua b/lua/opencode/api.lua
index c4b63f96..52031a24 100644
--- a/lua/opencode/api.lua
+++ b/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,
diff --git a/lua/opencode/commands/handlers/workflow.lua b/lua/opencode/commands/handlers/workflow.lua
index b0e252ac..834a4eeb 100644
--- a/lua/opencode/commands/handlers/workflow.lua
+++ b/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,
diff --git a/lua/opencode/config.lua b/lua/opencode/config.lua
index c38bb1e5..9193bb53 100644
--- a/lua/opencode/config.lua
+++ b/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 = {
diff --git a/lua/opencode/types.lua b/lua/opencode/types.lua
index 510853cd..c3064dd1 100644
--- a/lua/opencode/types.lua
+++ b/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
@@ -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
diff --git a/lua/opencode/ui/formatter.lua b/lua/opencode/ui/formatter.lua
index ca8f2426..0d5b505e 100644
--- a/lua/opencode/ui/formatter.lua
+++ b/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')
 
@@ -664,6 +688,12 @@ 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
 
diff --git a/lua/opencode/ui/renderer.lua b/lua/opencode/ui/renderer.lua
index cd0590d8..62bdb8d6 100644
--- a/lua/opencode/ui/renderer.lua
+++ b/lua/opencode/ui/renderer.lua
@@ -9,6 +9,234 @@ local flush = require('opencode.ui.renderer.flush')
 local scroll = require('opencode.ui.renderer.scroll')
 
 local M = {}
+local HIDDEN_MESSAGES_NOTICE_MESSAGE_ID = '__opencode_hidden_messages_notice__'
+local HIDDEN_MESSAGES_NOTICE_PART_ID = '__opencode_hidden_messages_notice_part__'
+
+---@return integer|nil
+local function get_max_rendered_messages()
+  local limit = config.ui and config.ui.output and config.ui.output.max_messages
+  if type(limit) ~= 'number' or limit <= 0 then
+    return nil
+  end
+  return math.floor(limit)
+end
+
+---@param message OpencodeMessage|nil
+---@return boolean
+local function is_renderer_synthetic_message(message)
+  local message_id = message and message.info and message.info.id
+  return message_id == '__opencode_revert_message__' or message_id == HIDDEN_MESSAGES_NOTICE_MESSAGE_ID
+end
+
+---@param message OpencodeMessage|nil
+---@return boolean
+local function is_active_session_message(message)
+  local session_id = message and message.info and message.info.sessionID
+  return session_id ~= nil and state.active_session and state.active_session.id == session_id
+end
+
+---@param messages OpencodeMessage[]|nil
+---@return OpencodeMessage[]
+local function get_real_session_messages(messages)
+  return vim.tbl_filter(function(message)
+    return is_active_session_message(message) and not is_renderer_synthetic_message(message)
+  end, messages or {})
+end
+
+---@param messages OpencodeMessage[]|nil
+---@return integer|nil
+local function get_revert_index(messages)
+  local revert = state.active_session and state.active_session.revert
+  local revert_message_id = revert and revert.messageID
+  if not revert_message_id then
+    return nil
+  end
+
+  local real_messages = get_real_session_messages(messages)
+  for i, message in ipairs(real_messages) do
+    if message.info and message.info.id == revert_message_id then
+      return i
+    end
+  end
+
+  return nil
+end
+
+---@param messages OpencodeMessage[]|nil
+---@return OpencodeMessage[] visible_messages
+---@return integer hidden_count
+local function get_visible_session_messages(messages)
+  local real_messages = get_real_session_messages(messages)
+  local revert_index = get_revert_index(messages)
+  if revert_index then
+    real_messages = vim.list_slice(real_messages, 1, revert_index - 1)
+  end
+
+  local limit = get_max_rendered_messages()
+  if not limit or #real_messages <= limit then
+    return real_messages, 0
+  end
+
+  local start_index = #real_messages - limit + 1
+  return vim.list_slice(real_messages, start_index, #real_messages), start_index - 1
+end
+
+---@param hidden_count integer
+---@return OpencodeMessage
+local function build_hidden_messages_notice(hidden_count)
+  local session_id = state.active_session and state.active_session.id or ''
+  return {
+    info = {
+      id = HIDDEN_MESSAGES_NOTICE_MESSAGE_ID,
+      sessionID = session_id,
+      role = 'system',
+    },
+    parts = {
+      {
+        id = HIDDEN_MESSAGES_NOTICE_PART_ID,
+        messageID = HIDDEN_MESSAGES_NOTICE_MESSAGE_ID,
+        sessionID = session_id,
+        type = 'hidden-messages-display',
+        state = {
+          hidden_count = hidden_count,
+        },
+      },
+    },
+  }
+end
+
+---@param message_id string
+---@return OpencodeMessage|nil
+local function find_message_in_state(message_id)
+  for _, message in ipairs(state.messages or {}) do
+    if message.info and message.info.id == message_id then
+      return message
+    end
+  end
+  return nil
+end
+
+---@param message OpencodeMessage
+local function ensure_message_rendered(message)
+  local message_id = message.info and message.info.id
+  if not message_id or ctx.render_state:get_message(message_id) then
+    return
+  end
+
+  ctx.render_state:set_message(message)
+  flush.mark_message_dirty(message_id)
+
+  for _, part in ipairs(message.parts or {}) do
+    if part.id and part.type ~= 'step-start' and part.type ~= 'step-finish' then
+      ctx.render_state:set_part(part)
+      flush.mark_part_dirty(part.id, message_id)
+    end
+  end
+end
+
+---@param hidden_count integer
+local function upsert_hidden_messages_notice(hidden_count)
+  local existing_message = ctx.render_state:get_message(HIDDEN_MESSAGES_NOTICE_MESSAGE_ID)
+  local notice_message = build_hidden_messages_notice(hidden_count)
+
+  if not existing_message then
+    ensure_message_rendered(notice_message)
+  else
+    local existing_part = ctx.render_state:get_part(HIDDEN_MESSAGES_NOTICE_PART_ID)
+    if not existing_part or not existing_part.part then
+      hide_rendered_message(HIDDEN_MESSAGES_NOTICE_MESSAGE_ID)
+      ensure_message_rendered(notice_message)
+    else
+      ctx.render_state:set_message(notice_message, existing_message.line_start, existing_message.line_end)
+      ctx.render_state:set_part(notice_message.parts[1], existing_part.line_start, existing_part.line_end)
+    end
+  end
+
+  local part_data = ctx.render_state:get_part(HIDDEN_MESSAGES_NOTICE_PART_ID)
+  if part_data then
+    ctx.render_state:add_actions(HIDDEN_MESSAGES_NOTICE_PART_ID, {
+      {
+        text = 'Toggle Max Messages',
+        type = 'toggle_max_messages',
+        args = {},
+        key = 'm',
+        range = { from = part_data.line_start, to = part_data.line_end },
+        display_line = part_data.line_start,
+      },
+    })
+    flush.mark_part_dirty(HIDDEN_MESSAGES_NOTICE_PART_ID, HIDDEN_MESSAGES_NOTICE_MESSAGE_ID)
+  end
+end
+
+---@param message_id string
+local function hide_rendered_message(message_id)
+  local rendered_message = ctx.render_state:get_message(message_id)
+  local message = rendered_message and rendered_message.message or find_message_in_state(message_id)
+  if not message then
+    return
+  end
+
+  ctx.render_state:clear_orphan_parts(message_id)
+  for _, part in ipairs(message.parts or {}) do
+    if part.id then
+      flush.queue_part_removal(part.id)
+    end
+  end
+  flush.queue_message_removal(message_id)
+end
+
+local function reconcile_rendered_message_limit()
+  if not state.active_session or not state.messages then
+    return
+  end
+
+  local limit = get_max_rendered_messages()
+  if not limit then
+    if ctx.render_state:get_message(HIDDEN_MESSAGES_NOTICE_MESSAGE_ID) then
+      hide_rendered_message(HIDDEN_MESSAGES_NOTICE_MESSAGE_ID)
+    end
+    return
+  end
+
+  local visible_messages, hidden_count = get_visible_session_messages(state.messages)
+  local visible_ids = {}
+  for _, message in ipairs(visible_messages) do
+    local message_id = message.info and message.info.id
+    if message_id then
+      visible_ids[message_id] = true
+      ensure_message_rendered(message)
+    end
+  end
+
+  for _, message in ipairs(get_real_session_messages(state.messages)) do
+    local message_id = message.info and message.info.id
+    if message_id and not visible_ids[message_id] and ctx.render_state:get_message(message_id) then
+      hide_rendered_message(message_id)
+    end
+  end
+
+  if hidden_count > 0 then
+    upsert_hidden_messages_notice(hidden_count)
+  elseif ctx.render_state:get_message(HIDDEN_MESSAGES_NOTICE_MESSAGE_ID) then
+    hide_rendered_message(HIDDEN_MESSAGES_NOTICE_MESSAGE_ID)
+  end
+end
+
+---@param message_id string|nil
+---@return boolean
+local function is_message_visible(message_id)
+  if not message_id then
+    return false
+  end
+
+  for _, message in ipairs(select(1, get_visible_session_messages(state.messages))) do
+    if message.info and message.info.id == message_id then
+      return true
+    end
+  end
+
+  return false
+end
 
 -- Expose event handlers on M so tests can call them directly and subscriptions
 -- can be stubbed cleanly (e.g. stub(renderer, '_render_full_session_data'))
@@ -100,22 +328,35 @@ end
 function M._render_full_session_data(session_data, opts)
   opts = opts or {}
   M.reset()
+  state.renderer.set_messages(vim.deepcopy(session_data or {}))
 
   if not state.active_session or not state.messages then
     return
   end
 
-  local revert_index = nil
+  local visible_messages, hidden_count = get_visible_session_messages(state.messages)
+  local revert_index = get_revert_index(state.messages)
 
   flush.begin_bulk_mode()
 
-  for i, msg in ipairs(session_data) do
-    if state.active_session.revert and state.active_session.revert.messageID == msg.info.id then
-      revert_index = i
-    end
-    events.on_message_updated({ info = msg.info }, revert_index)
+  if hidden_count > 0 then
+    local hidden_notice = build_hidden_messages_notice(hidden_count)
+    events.on_message_updated(hidden_notice)
+    events.on_part_updated({ part = hidden_notice.parts[1] })
+  end
+
+  for _, msg in ipairs(visible_messages) do
+    events.on_message_updated({ info = msg.info })
     for _, part in ipairs(msg.parts or {}) do
-      events.on_part_updated({ part = part }, revert_index)
+      events.on_part_updated({ part = part })
+    end
+  end
+
+  for _, msg in ipairs(state.messages) do
+    if msg.info and msg.info.sessionID ~= state.active_session.id then
+      for _, part in ipairs(msg.parts or {}) do
+        events.on_part_updated({ part = part })
+      end
     end
   end
 
@@ -234,6 +475,9 @@ function M.on_session_changed(_, new, old)
   end
 end
 
+M.reconcile_rendered_message_limit = reconcile_rendered_message_limit
+M.is_message_visible = is_message_visible
+
 ---Scroll to bottom after all queued events have been processed
 function M.on_emit_events_finished()
   M.scroll_to_bottom()
diff --git a/lua/opencode/ui/renderer/buffer.lua b/lua/opencode/ui/renderer/buffer.lua
index 3287dda1..770630d5 100644
--- a/lua/opencode/ui/renderer/buffer.lua
+++ b/lua/opencode/ui/renderer/buffer.lua
@@ -9,12 +9,22 @@ local pinned_bottom_message_ids = {
   ['question-display-message'] = true,
 }
 
+local pinned_top_message_ids = {
+  ['__opencode_hidden_messages_notice__'] = true,
+}
+
 ---@param message_id string|nil
 ---@return boolean
 local function is_pinned_bottom_message(message_id)
   return message_id ~= nil and pinned_bottom_message_ids[message_id] == true
 end
 
+---@param message_id string|nil
+---@return boolean
+local function is_pinned_top_message(message_id)
+  return message_id ~= nil and pinned_top_message_ids[message_id] == true
+end
+
 ---@param extmarks table<number, OutputExtmark[]|fun(): OutputExtmark>[]|table<number, OutputExtmark[]>|nil
 ---@return boolean
 local function has_extmarks(extmarks)
@@ -247,6 +257,10 @@ local function get_message_insert_line(message_id)
     return rendered_message.line_start
   end
 
+  if is_pinned_top_message(message_id) then
+    return 0
+  end
+
   local line_count = output_window.get_buf_line_count()
   local append_at = math.max(line_count - 1, 0)
   if line_count == 1 then
diff --git a/lua/opencode/ui/renderer/events.lua b/lua/opencode/ui/renderer/events.lua
index 96a2dc2d..28be67e1 100644
--- a/lua/opencode/ui/renderer/events.lua
+++ b/lua/opencode/ui/renderer/events.lua
@@ -33,6 +33,22 @@ local function find_text_part_for_message(message)
   return nil
 end
 
+---@param message_id string|nil
+---@return OpencodeMessage|nil
+local function find_message_in_state(message_id)
+  if not message_id then
+    return nil
+  end
+
+  for _, message in ipairs(state.messages or {}) do
+    if message.info and message.info.id == message_id then
+      return message
+    end
+  end
+
+  return nil
+end
+
 -- Lazy require to avoid circular dependency: renderer.lua <-> events.lua
 ---@param force? boolean
 local function scroll(force)
@@ -171,18 +187,23 @@ function M.on_message_updated(message, revert_index)
   end
 
   local rendered_message = ctx.render_state:get_message(msg.info.id)
-  local found_msg = rendered_message and rendered_message.message
+  local found_msg = rendered_message and rendered_message.message or find_message_in_state(msg.info.id)
 
   if revert_index then
     if not found_msg then
       table.insert(state.messages, msg)
+      found_msg = msg
     end
-    ctx.render_state:set_message(msg, 0, 0)
+    ctx.render_state:set_message(found_msg, 0, 0)
     replay_orphan_parts(msg.info.id, revert_index)
     return
   end
 
   if found_msg then
+    if not rendered_message then
+      ctx.render_state:set_message(found_msg)
+      flush.mark_message_dirty(msg.info.id)
+    end
     local error_changed = not vim.deep_equal(found_msg.info.error, msg.info.error)
     found_msg.info = msg.info
 
@@ -210,6 +231,10 @@ function M.on_message_updated(message, revert_index)
   end
 
   update_stats(msg)
+
+  if not revert_index and not ctx.bulk_mode and msg.info.id ~= '__opencode_hidden_messages_notice__' then
+    require('opencode.ui.renderer').reconcile_rendered_message_limit()
+  end
 end
 
 ---Handle message.removed — remove the message and all its parts from the buffer
@@ -225,12 +250,13 @@ function M.on_message_removed(properties)
   end
 
   local rendered_message = ctx.render_state:get_message(message_id)
+  local message = rendered_message and rendered_message.message or find_message_in_state(message_id)
   ctx.render_state:clear_orphan_parts(message_id)
-  if not rendered_message or not rendered_message.message then
+  if not message then
     return
   end
 
-  for _, part in ipairs(rendered_message.message.parts or {}) do
+  for _, part in ipairs(message.parts or {}) do
     if part.id then
       flush.queue_part_removal(part.id)
     end
@@ -244,6 +270,10 @@ function M.on_message_removed(properties)
       break
     end
   end
+
+  if not ctx.bulk_mode and message_id ~= '__opencode_hidden_messages_notice__' then
+    require('opencode.ui.renderer').reconcile_rendered_message_limit()
+  end
 end
 
 ---Handle message.part.updated — insert or replace a part in the buffer
@@ -272,6 +302,13 @@ function M.on_part_updated(properties, revert_index)
   end
 
   local rendered_message = ctx.render_state:get_message(part.messageID)
+  if not rendered_message then
+    local existing_message = find_message_in_state(part.messageID)
+    if existing_message then
+      ctx.render_state:set_message(existing_message)
+      rendered_message = ctx.render_state:get_message(part.messageID)
+    end
+  end
   if not rendered_message or not rendered_message.message then
     ctx.render_state:upsert_orphan_part(part.messageID, part)
     return
@@ -284,15 +321,30 @@ function M.on_part_updated(properties, revert_index)
   local is_new_part = not part_data
 
   local prev_last_part_id = get_last_part_for_message(message)
+  local existing_part_index = nil
+  for i = #message.parts, 1, -1 do
+    if message.parts[i].id == part.id then
+      existing_part_index = i
+      break
+    end
+  end
 
   -- Update the part reference in the message
   if is_new_part then
-    table.insert(message.parts, part)
+    if existing_part_index then
+      message.parts[existing_part_index] = part
+    else
+      table.insert(message.parts, part)
+    end
   else
-    for i = #message.parts, 1, -1 do
-      if message.parts[i].id == part.id then
-        message.parts[i] = part
-        break
+    if existing_part_index then
+      message.parts[existing_part_index] = part
+    else
+      for i = #message.parts, 1, -1 do
+        if message.parts[i].id == part.id then
+          message.parts[i] = part
+          break
+        end
       end
     end
   end
diff --git a/lua/opencode/ui/ui.lua b/lua/opencode/ui/ui.lua
index fe1684bc..d8178dbb 100644
--- a/lua/opencode/ui/ui.lua
+++ b/lua/opencode/ui/ui.lua
@@ -473,12 +473,14 @@ end
 ---from opencode
 ---@param synchronous? boolean If true, waits until session is fully rendered
 ---@param opts? {force_scroll?: boolean}
+---@return Promise<OpencodeMessage[]> | OpencodeMessage[] | nil
 function M.render_output(synchronous, opts)
   local ret = renderer.render_full_session(opts)
 
   if ret and synchronous then
     ret:wait()
   end
+  return ret
 end
 
 ---@param lines string[]
diff --git a/tests/replay/renderer_spec.lua b/tests/replay/renderer_spec.lua
index 042f5863..afd2e6d2 100644
--- a/tests/replay/renderer_spec.lua
+++ b/tests/replay/renderer_spec.lua
@@ -225,6 +225,205 @@ describe('renderer unit tests', function()
     assert.are.equal(1, #revert_messages)
   end)
 
+  it('limits rendered messages and inserts a hidden-messages notice', function()
+    local renderer = require('opencode.ui.renderer')
+
+    helpers.replay_setup()
+    config.ui.output.max_messages = 2
+
+    state.session.set_active({
+      id = 'ses_123',
+      title = 'Session',
+      time = { created = 1, updated = 1 },
+    })
+
+    renderer._render_full_session_data({
+      {
+        info = { id = 'msg_1', role = 'user', sessionID = 'ses_123', time = { created = 1 } },
+        parts = {
+          { id = 'part_1', messageID = 'msg_1', sessionID = 'ses_123', type = 'text', text = 'first' },
+        },
+      },
+      {
+        info = { id = 'msg_2', role = 'assistant', sessionID = 'ses_123', time = { created = 2 } },
+        parts = {
+          { id = 'part_2', messageID = 'msg_2', sessionID = 'ses_123', type = 'text', text = 'second' },
+        },
+      },
+      {
+        info = { id = 'msg_3', role = 'assistant', sessionID = 'ses_123', time = { created = 3 } },
+        parts = {
+          { id = 'part_3', messageID = 'msg_3', sessionID = 'ses_123', type = 'text', text = 'third' },
+        },
+      },
+    })
+
+    assert.is_not_nil(renderer.get_rendered_message('__opencode_hidden_messages_notice__'))
+    assert.is_nil(renderer.get_rendered_message('msg_1'))
+    assert.is_not_nil(renderer.get_rendered_message('msg_2'))
+    assert.is_not_nil(renderer.get_rendered_message('msg_3'))
+
+    local lines = vim.api.nvim_buf_get_lines(state.windows.output_buf, 0, -1, false)
+    assert.are.equal('> 1 older message is not displayed.', lines[1])
+
+    config.ui.output.max_messages = nil
+  end)
+
+  it('evicts the oldest rendered message during streaming updates', function()
+    local renderer = require('opencode.ui.renderer')
+    local events = require('opencode.ui.renderer.events')
+    local flush = require('opencode.ui.renderer.flush')
+
+    helpers.replay_setup()
+    config.ui.output.max_messages = 2
+
+    state.session.set_active({
+      id = 'ses_123',
+      title = 'Session',
+      time = { created = 1, updated = 1 },
+    })
+    state.renderer.set_messages({
+      {
+        info = { id = 'msg_1', role = 'user', sessionID = 'ses_123', time = { created = 1 } },
+        parts = {
+          { id = 'part_1', messageID = 'msg_1', sessionID = 'ses_123', type = 'text', text = 'first' },
+        },
+      },
+      {
+        info = { id = 'msg_2', role = 'assistant', sessionID = 'ses_123', time = { created = 2 } },
+        parts = {
+          { id = 'part_2', messageID = 'msg_2', sessionID = 'ses_123', type = 'text', text = 'second' },
+        },
+      },
+    })
+
+    renderer._render_full_session_data(state.messages)
+
+    events.on_message_updated({
+      info = { id = 'msg_3', role = 'assistant', sessionID = 'ses_123', time = { created = 3 } },
+      parts = {},
+    })
+    events.on_part_updated({
+      part = { id = 'part_3', messageID = 'msg_3', sessionID = 'ses_123', type = 'text', text = 'third' },
+    })
+    flush.flush()
+
+    assert.is_nil(renderer.get_rendered_message('msg_1'))
+    assert.is_not_nil(renderer.get_rendered_message('msg_2'))
+    assert.is_not_nil(renderer.get_rendered_message('msg_3'))
+
+    local lines = vim.api.nvim_buf_get_lines(state.windows.output_buf, 0, -1, false)
+    assert.are.equal('> 1 older message is not displayed.', lines[1])
+
+    config.ui.output.max_messages = nil
+  end)
+
+  it('updates the hidden-messages notice when an older hidden message is removed', function()
+    local renderer = require('opencode.ui.renderer')
+    local events = require('opencode.ui.renderer.events')
+    local flush = require('opencode.ui.renderer.flush')
+
+    helpers.replay_setup()
+    config.ui.output.max_messages = 2
+
+    state.session.set_active({
+      id = 'ses_123',
+      title = 'Session',
+      time = { created = 1, updated = 1 },
+    })
+
+    renderer._render_full_session_data({
+      {
+        info = { id = 'msg_1', role = 'user', sessionID = 'ses_123', time = { created = 1 } },
+        parts = {
+          { id = 'part_1', messageID = 'msg_1', sessionID = 'ses_123', type = 'text', text = 'first' },
+        },
+      },
+      {
+        info = { id = 'msg_2', role = 'assistant', sessionID = 'ses_123', time = { created = 2 } },
+        parts = {
+          { id = 'part_2', messageID = 'msg_2', sessionID = 'ses_123', type = 'text', text = 'second' },
+        },
+      },
+      {
+        info = { id = 'msg_3', role = 'assistant', sessionID = 'ses_123', time = { created = 3 } },
+        parts = {
+          { id = 'part_3', messageID = 'msg_3', sessionID = 'ses_123', type = 'text', text = 'third' },
+        },
+      },
+      {
+        info = { id = 'msg_4', role = 'assistant', sessionID = 'ses_123', time = { created = 4 } },
+        parts = {
+          { id = 'part_4', messageID = 'msg_4', sessionID = 'ses_123', type = 'text', text = 'fourth' },
+        },
+      },
+    })
+
+    events.on_message_removed({ sessionID = 'ses_123', messageID = 'msg_1' })
+    flush.flush()
+
+    local lines = vim.api.nvim_buf_get_lines(state.windows.output_buf, 0, -1, false)
+    assert.are.equal('> 1 older message is not displayed.', lines[1])
+
+    config.ui.output.max_messages = nil
+  end)
+
+  it('updates the hidden-messages notice count after multiple hidden removals', function()
+    local renderer = require('opencode.ui.renderer')
+    local events = require('opencode.ui.renderer.events')
+    local flush = require('opencode.ui.renderer.flush')
+
+    helpers.replay_setup()
+    config.ui.output.max_messages = 2
+
+    state.session.set_active({
+      id = 'ses_123',
+      title = 'Session',
+      time = { created = 1, updated = 1 },
+    })
+
+    renderer._render_full_session_data({
+      {
+        info = { id = 'msg_1', role = 'user', sessionID = 'ses_123', time = { created = 1 } },
+        parts = {
+          { id = 'part_1', messageID = 'msg_1', sessionID = 'ses_123', type = 'text', text = 'first' },
+        },
+      },
+      {
+        info = { id = 'msg_2', role = 'assistant', sessionID = 'ses_123', time = { created = 2 } },
+        parts = {
+          { id = 'part_2', messageID = 'msg_2', sessionID = 'ses_123', type = 'text', text = 'second' },
+        },
+      },
+      {
+        info = { id = 'msg_3', role = 'assistant', sessionID = 'ses_123', time = { created = 3 } },
+        parts = {
+          { id = 'part_3', messageID = 'msg_3', sessionID = 'ses_123', type = 'text', text = 'third' },
+        },
+      },
+      {
+        info = { id = 'msg_4', role = 'assistant', sessionID = 'ses_123', time = { created = 4 } },
+        parts = {
+          { id = 'part_4', messageID = 'msg_4', sessionID = 'ses_123', type = 'text', text = 'fourth' },
+        },
+      },
+    })
+
+    events.on_message_removed({ sessionID = 'ses_123', messageID = 'msg_1' })
+    flush.flush()
+
+    local lines = vim.api.nvim_buf_get_lines(state.windows.output_buf, 0, -1, false)
+    assert.are.equal('> 1 older message is not displayed.', lines[1])
+
+    events.on_message_removed({ sessionID = 'ses_123', messageID = 'msg_2' })
+    flush.flush()
+
+    lines = vim.api.nvim_buf_get_lines(state.windows.output_buf, 0, -1, false)
+    assert.are.equal('----', lines[1])
+
+    config.ui.output.max_messages = nil
+  end)
+
   it('ignores session.updated for non-active session IDs', function()
     local renderer = require('opencode.ui.renderer')