feat(timeline-picker): implement basic timeline picker

lua/opencode/api.lua

@@ -680,6 +680,63 @@ function M.undo(messageId)
     end)
 end
 
+function M.timeline()
+  local user_messages = {}
+  for _, msg in ipairs(state.messages or {}) do
+    local parts = msg.parts or {}
+    local is_summary = #parts == 1 and parts[1].synthetic == true
+    if msg.info.role == 'user' and not is_summary then
+      table.insert(user_messages, msg)
+    end
+  end
+  if #user_messages == 0 then
+    vim.notify('No user messages in the current session', vim.log.levels.WARN)
+    return
+  end
+
+  local timeline_picker = require('opencode.ui.timeline_picker')
+  timeline_picker.pick(user_messages, function(selected_msg)
+    if selected_msg then
+      require('opencode.ui.navigation').goto_message_by_id(selected_msg.info.id)
+    end
+  end)
+end
+
+--- Forks the current session from a specific user message.
+---@param message_id? string The ID of the user message to fork from. If not provided, uses the last user message.
+function M.fork_session(message_id)
+  if not state.active_session then
+    vim.notify('No active session to fork', vim.log.levels.WARN)
+    return
+  end
+
+  local message_to_fork = message_id or state.last_user_message and state.last_user_message.info.id
+  if not message_to_fork then
+    vim.notify('No user message to fork from', vim.log.levels.WARN)
+    return
+  end
+
+  state.api_client
+    :fork_session(state.active_session.id, {
+      messageID = message_to_fork,
+    })
+    :and_then(function(response)
+      vim.schedule(function()
+        if response and response.id then
+          vim.notify('Session forked successfully. New session ID: ' .. response.id, vim.log.levels.INFO)
+          core.switch_session(response.id)
+        else
+          vim.notify('Session forked but no new session ID received', vim.log.levels.WARN)
+        end
+      end)
+    end)
+    :catch(function(err)
+      vim.schedule(function()
+        vim.notify('Failed to fork session: ' .. vim.inspect(err), vim.log.levels.ERROR)
+      end)
+    end)
+end
+
 -- Returns the ID of the next user message after the current undo point
 -- This is a port of the opencode tui logic
 -- https://github.com/sst/opencode/blob/dev/packages/tui/internal/components/chat/messages.go#L1199
@@ -1074,6 +1131,11 @@ M.commands = {
       end
     end,
   },
+
+  timeline = {
+    desc = 'Open timeline picker to navigate/undo/redo/fork to message',
+    fn = M.timeline,
+  },
 }
 
 M.slash_commands_map = {
@@ -1089,6 +1151,7 @@ M.slash_commands_map = {
   ['/redo'] = { fn = M.redo, desc = 'Redo last action' },
   ['/sessions'] = { fn = M.select_session, desc = 'Select session' },
   ['/share'] = { fn = M.share, desc = 'Share current session' },
+  ['/timeline'] = { fn = M.timeline, desc = 'Open timeline picker' },
   ['/undo'] = { fn = M.undo, desc = 'Undo last action' },
   ['/unshare'] = { fn = M.unshare, desc = 'Unshare current session' },
 }

lua/opencode/api_client.lua

@@ -213,6 +213,15 @@ function OpencodeApiClient:summarize_session(id, summary_data, directory)
   return self:_call('/session/' .. id .. '/summarize', 'POST', summary_data, { directory = directory })
 end
 
+--- Fork an existing session at a specific message
+--- @param id string Session ID (required)
+--- @param fork_data {messageID?: string}|nil Fork data
+--- @param directory string|nil Directory path
+--- @return Promise<Session>
+function OpencodeApiClient:fork_session(id, fork_data, directory)
+  return self:_call('/session/' .. id .. '/fork', 'POST', fork_data, { directory = directory })
+end
+
 -- Message endpoints
 
 --- List messages for a session

lua/opencode/config.lua

@@ -19,6 +19,7 @@ M.defaults = {
       ['<leader>oI'] = { 'open_input_new_session', desc = 'Open input (new session)' },
       ['<leader>oo'] = { 'open_output', desc = 'Open output window' },
       ['<leader>ot'] = { 'toggle_focus', desc = 'Toggle focus' },
+      ['<leader>oT'] = { 'timeline', desc = 'Session timeline' },
       ['<leader>oq'] = { 'close', desc = 'Close Opencode window' },
       ['<leader>os'] = { 'select_session', desc = 'Select session' },
       ['<leader>op'] = { 'configure_provider', desc = 'Configure provider' },
@@ -75,12 +76,17 @@ M.defaults = {
       delete_session = { '<C-d>' },
       new_session = { '<C-n>' },
     },
+    timeline_picker = {
+      undo = { '<C-u>', mode = { 'i', 'n' } },
+      fork = { '<C-f>', mode = { 'i', 'n' } },
+    },
   },
   ui = {
     position = 'right',
     input_position = 'bottom',
     window_width = 0.40,
     input_height = 0.15,
+    picker_width = 100,
     display_model = true,
     display_context_size = true,
     display_cost = true,
@@ -172,6 +178,7 @@ M.defaults = {
   debug = {
     enabled = false,
     capture_streamed_events = false,
+    show_ids = false,
   },
   prompt_guard = nil,
 }

lua/opencode/core.lua

@@ -25,21 +25,24 @@ function M.select_session(parent_id)
       end
       return
     end
-    -- clear the model so it can be set by the session. If it doesn't get set
-    -- then core.get_model() will reset it to the default
-    state.current_model = nil
-    state.active_session = selected_session
-    if state.windows then
-      state.restore_points = {}
-      -- Don't need to update either renderer because they subscribe to
-      -- session changes
-      ui.focus_input()
-    else
-      M.open()
-    end
+    M.switch_session(selected_session.id)
   end)
 end
 
+function M.switch_session(session_id)
+  local selected_session = session.get_by_id(session_id)
+  -- clear the model so it can be set by the session. If it doesn't get set
+  -- then core.get_model() will reset it to the default
+  state.current_model = nil
+  state.active_session = selected_session
+  if state.windows then
+    state.restore_points = {}
+    ui.focus_input()
+  else
+    M.open()
+  end
+end
+
 ---@param opts? OpenOpts
 function M.open(opts)
   opts = opts or { focus = 'input', new_session = false }

lua/opencode/git_review.lua

@@ -365,7 +365,7 @@ function M.with_restore_point(restore_point_id, fn)
         item.files and #item.files or 0,
         item.deleted_files and #item.deleted_files or 0,
         item.id:sub(1, 8),
-        utils.time_ago(item.created_at) or 'unknown',
+        utils.format_time(item.created_at) or 'unknown',
         item.from_snapshot_id and item.from_snapshot_id:sub(1, 8) or 'none'
       )
     end,

lua/opencode/init.lua

@@ -8,6 +8,7 @@ function M.setup(opts)
   local config = require('opencode.config')
   config.setup(opts)
 
+  require('opencode.ui.highlight').setup()
   require('opencode.core').setup()
   require('opencode.api').setup()
   require('opencode.keymap').setup(config.keymap)

lua/opencode/types.lua

@@ -72,11 +72,16 @@
 ---@field output_window OpencodeKeymapOutputWindow
 ---@field permission OpencodeKeymapPermission
 ---@field session_picker OpencodeSessionPickerKeymap
+---@field timeline_picker OpencodeTimelinePickerKeymap
 
 ---@class OpencodeSessionPickerKeymap
 ---@field delete_session OpencodeKeymapEntry
 ---@field new_session OpencodeKeymapEntry
 
+---@class OpencodeTimelinePickerKeymap
+---@field undo OpencodeKeymapEntry
+---@field fork OpencodeKeymapEntry
+
 ---@class OpencodeCompletionFileSourcesConfig
 ---@field enabled boolean
 ---@field preferred_cli_tool 'server'|'fd'|'fdfind'|'rg'|'git'
@@ -95,6 +100,7 @@
 ---@field input_position 'bottom'|'top' # Position of the input window (default: 'bottom')
 ---@field window_width number
 ---@field input_height number
+---@field picker_width number|nil # Default width for all pickers (nil uses current window width)
 ---@field display_model boolean
 ---@field display_context_size boolean
 ---@field display_cost boolean
@@ -126,6 +132,7 @@
 ---@class OpencodeDebugConfig
 ---@field enabled boolean
 ---@field capture_streamed_events boolean
+---@field show_ids boolean
 
 --- @class OpencodeProviders
 --- @field [string] string[]