feat(output): preview latest N lines below closed folds

Add a new ui.output.tools setting only_show_latest_n that keeps the latest
N lines visible below a closed fold for long-running tool output. Update
folding logic to compute fold endpoints respecting this preview count,
update fold text to mention the preview when enabled, lower the default
folding threshold.

Author: sudo-tee

README.md

@@ -236,12 +236,13 @@ require('opencode').setup({
     },
     output = {
       filetype = 'opencode_output', -- Filetype assigned to the output buffer (default: 'opencode_output')
-       compact_assistant_headers = false, -- 'full' (default), 'minimal' (compact if same mode), or 'hidden' (no headers for assistant)
+      compact_assistant_headers = false, -- 'full' (default), 'minimal' (compact if same mode), or 'hidden' (no headers for assistant)
       tools = {
         show_output = true, -- Show tools output [diffs, cmd output, etc.] (default: true)
         show_reasoning_output = true, -- Show reasoning/thinking steps output (default: true)
         use_folds = true, -- Use folds for tool output (default: true)
-        folding_threshold = 5, -- Number of lines to show before folding when show_output is true (default: 5)
+        only_show_latest_n = nil, -- Keep the latest N lines visible below a closed fold; nil keeps the current behavior (default: nil)
+        folding_threshold = 25, -- Number of leading lines to keep visible before folding when show_output is true (default: 25)
       },
       rendering = {
         markdown_debounce_ms = 250, -- Debounce time for markdown rendering on new data (default: 250ms)

lua/opencode/config.lua

@@ -177,6 +177,8 @@ M.defaults = {
         show_output = true,
         show_reasoning_output = true,
         use_folds = true,
+        -- Keep the latest N lines visible below folds for long-running progress.
+        only_show_latest_n = 3,
         -- Reduced default threshold to make small tool outputs foldable by default.
         -- Users can override this in their config if they prefer the previous value.
         folding_threshold = 25,

lua/opencode/types.lua

@@ -254,7 +254,7 @@
 
 ---@class OpencodeUIOutputConfig
 ---@field time_format string|nil # Custom os.date format for timestamps, e.g. '%m/%d %H:%M'. Uses fixed default when nil.
----@field tools { show_output: boolean, show_reasoning_output: boolean, use_folds: boolean, folding_threshold: number }
+---@field tools { show_output: boolean, show_reasoning_output: boolean, use_folds: boolean, folding_threshold: number, only_show_latest_n: integer|nil }
 ---@field rendering OpencodeUIOutputRenderingConfig
 ---@field max_messages integer|nil
 ---@field always_scroll_to_bottom boolean

lua/opencode/ui/output.lua

@@ -103,14 +103,26 @@ function Output:add_fold_with_threshold(start_line, show, use_folds)
   end
 
   local threshold = config.ui.output.tools.folding_threshold or 5
+  local only_show_latest_n = config.ui.output.tools.only_show_latest_n
+  if type(only_show_latest_n) ~= 'number' or only_show_latest_n < 1 then
+    only_show_latest_n = 0
+  else
+    only_show_latest_n = math.floor(only_show_latest_n)
+  end
+
   local end_line = self:get_line_count()
 
   if not show then
-    if end_line > start_line then
-      self:add_fold(start_line, end_line)
+    local fold_end = end_line - only_show_latest_n
+    if fold_end >= start_line then
+      self:add_fold(start_line, fold_end)
     end
   elseif end_line > start_line + threshold then
-    self:add_fold(start_line + threshold, end_line)
+    local fold_start = start_line + threshold
+    local fold_end = end_line - only_show_latest_n
+    if fold_end >= fold_start then
+      self:add_fold(fold_start, fold_end)
+    end
   end
 end
 

lua/opencode/ui/output_window.lua

@@ -339,6 +339,13 @@ function M.fold_text()
   local windows = state.windows
   local output_buf = windows and windows.output_buf
   local line = vim.v.foldstart
+  local latest_n = config.ui.output.tools.only_show_latest_n
+
+  if type(latest_n) ~= 'number' or latest_n < 1 then
+    latest_n = nil
+  else
+    latest_n = math.floor(latest_n)
+  end
 
   if not output_buf or not vim.api.nvim_buf_is_valid(output_buf) then
     return vim.fn.foldtext()
@@ -355,7 +362,12 @@ function M.fold_text()
   end
 
   if line_count > 0 then
-    local text = string.format('▶ %d lines hidden (zo open, zc close) ◀', line_count)
+    local text
+    if latest_n then
+      text = string.format('▶ %d lines hidden, latest %d below (zo open, zc close) ◀', line_count, latest_n)
+    else
+      text = string.format('▶ %d lines hidden (zo open, zc close) ◀', line_count)
+    end
     local width = vim.api.nvim_win_get_width(0)
     local padding = math.max(0, math.floor((width - #text) / 2))
     return string.rep('-', padding) .. text .. string.rep('-', padding)

tests/unit/output_spec.lua

@@ -0,0 +1,94 @@
+local config = require('opencode.config')
+local Output = require('opencode.ui.output')
+
+describe('output fold thresholds', function()
+  local original_config
+
+  before_each(function()
+    original_config = vim.deepcopy(config.values)
+    config.values = vim.deepcopy(config.defaults)
+  end)
+
+  after_each(function()
+    config.values = original_config
+  end)
+
+it('uses the default latest-line preview when only_show_latest_n is not overridden', function()
+  config.setup({
+    ui = {
+      output = {
+        tools = {
+          folding_threshold = 3,
+          },
+        },
+      },
+    })
+
+    local output = Output.new()
+    output:add_lines({ '1', '2', '3', '4', '5', '6', '7' })
+
+  output:add_fold_with_threshold(1, true, true)
+
+  assert.same({ { from = 4, to = 4 } }, output.fold_ranges)
+end)
+
+it('preserves the current fold behavior when only_show_latest_n is explicitly disabled', function()
+  config.setup({
+    ui = {
+      output = {
+        tools = {
+          folding_threshold = 3,
+          only_show_latest_n = 0,
+        },
+      },
+    },
+  })
+
+  local output = Output.new()
+  output:add_lines({ '1', '2', '3', '4', '5', '6', '7' })
+
+  output:add_fold_with_threshold(1, true, true)
+
+  assert.same({ { from = 4, to = 7 } }, output.fold_ranges)
+end)
+
+  it('keeps the latest lines visible below folds when output is shown', function()
+    config.setup({
+      ui = {
+        output = {
+          tools = {
+            folding_threshold = 3,
+            only_show_latest_n = 2,
+          },
+        },
+      },
+    })
+
+    local output = Output.new()
+    output:add_lines({ '1', '2', '3', '4', '5', '6', '7' })
+
+    output:add_fold_with_threshold(1, true, true)
+
+    assert.same({ { from = 4, to = 5 } }, output.fold_ranges)
+  end)
+
+  it('keeps the latest lines visible when output is otherwise hidden', function()
+    config.setup({
+      ui = {
+        output = {
+          tools = {
+            show_output = false,
+            only_show_latest_n = 2,
+          },
+        },
+      },
+    })
+
+    local output = Output.new()
+    output:add_lines({ '1', '2', '3', '4', '5', '6', '7' })
+
+    output:add_fold_with_threshold(1, false, true)
+
+    assert.same({ { from = 1, to = 5 } }, output.fold_ranges)
+  end)
+end)

tests/unit/output_window_spec.lua

@@ -211,6 +211,52 @@ describe('output_window.setup', function()
   end)
 end)
 
+describe('output_window.fold_text', function()
+  local buf
+  local win
+
+  before_each(function()
+    buf = vim.api.nvim_create_buf(false, true)
+    win = vim.api.nvim_open_win(buf, true, {
+      relative = 'editor',
+      width = 100,
+      height = 10,
+      row = 0,
+      col = 0,
+    })
+    state.ui.set_windows({ output_buf = buf, output_win = win })
+    output_window.setup({ output_buf = buf, output_win = win })
+    output_window.set_lines({ 'a', 'b', 'c', 'd', 'e', 'f' })
+  end)
+
+  after_each(function()
+    state.ui.set_windows(nil)
+    pcall(vim.api.nvim_win_close, win, true)
+    pcall(vim.api.nvim_buf_delete, buf, { force = true })
+  end)
+
+  it('mentions visible latest lines when latest preview is enabled', function()
+    config.setup({
+      ui = {
+        output = {
+          tools = {
+            only_show_latest_n = 2,
+          },
+        },
+      },
+    })
+
+    output_window.set_folds({ { from = 2, to = 4 } })
+
+    local text = vim.api.nvim_win_call(win, function()
+      vim.v.foldstart = 2
+      return output_window.fold_text()
+    end)
+
+    assert.is_truthy(text:find('3 lines hidden, latest 2 below', 1, true))
+  end)
+end)
+
 describe('output_window extmarks', function()
   local buf