refactor(ui/navigation): use renderer state for message navigation

Replace manual extmark scanning and header detection with the renderer API.
Use renderer.get_rendered_message, get_next_rendered_message and
get_prev_rendered_message and simplify cursor positioning to use
rendered_msg.line_start + 1. Remove dependency on output_window and the
is_message_header helper.

This should fix #348

Author: sudo-tee

lua/opencode/ui/navigation.lua

@@ -1,24 +1,7 @@
 local M = {}
 
 local state = require('opencode.state')
-local output_window = require('opencode.ui.output_window')
-
-local function is_message_header(details)
-  local icons = require('opencode.ui.icons')
-  local header_user_icon = icons.get('header_user')
-  local header_assistant_icon = icons.get('header_assistant')
-
-  if not details or not details.virt_text then
-    return false
-  end
-
-  local first_virt_text = details.virt_text[1]
-  if not first_virt_text then
-    return false
-  end
-
-  return first_virt_text[1] == header_user_icon or first_virt_text[1] == header_assistant_icon
-end
+local renderer = require('opencode.ui.renderer')
 
 function M.goto_message_by_id(message_id)
   require('opencode.ui.ui').focus_output()
@@ -30,12 +13,11 @@ function M.goto_message_by_id(message_id)
     return
   end
 
-  local rendered_msg = require('opencode.ui.renderer').get_rendered_message(message_id)
+  local rendered_msg = renderer.get_rendered_message(message_id)
   if not rendered_msg or not rendered_msg.line_start then
     return
   end
-  local sep_offset = #require('opencode.ui.formatter').separator
-  vim.api.nvim_win_set_cursor(win, { rendered_msg.line_start + sep_offset, 0 })
+  vim.api.nvim_win_set_cursor(win, { rendered_msg.line_start + 1, 0 })
 end
 
 function M.goto_next_message()
@@ -49,23 +31,10 @@ function M.goto_next_message()
   end
 
   local current_line = vim.api.nvim_win_get_cursor(win)[1]
-
-  local extmarks = vim.api.nvim_buf_get_extmarks(
-    buf,
-    output_window.namespace,
-    { current_line, 0 },
-    -1,
-    { details = true }
-  )
-
-  for _, extmark in ipairs(extmarks) do
-    local line = extmark[2] + 1
-    local details = extmark[4]
-
-    if line > current_line and is_message_header(details) then
-      vim.api.nvim_win_set_cursor(win, { line, 0 })
-      return
-    end
+  local next_message = renderer.get_next_rendered_message(current_line)
+  if next_message and next_message.line_start then
+    vim.api.nvim_win_set_cursor(win, { next_message.line_start + 1, 0 })
+    return
   end
 
   local line_count = vim.api.nvim_buf_line_count(buf)
@@ -83,25 +52,12 @@ function M.goto_prev_message()
   end
 
   local current_line = vim.api.nvim_win_get_cursor(win)[1]
-
-  local extmarks = vim.api.nvim_buf_get_extmarks(
-    buf,
-    output_window.namespace,
-    0,
-    { current_line - 1, -1 },
-    { details = true }
-  )
-
-  for i = #extmarks, 1, -1 do
-    local extmark = extmarks[i]
-    local line = extmark[2] + 1
-    local details = extmark[4]
-
-    if line < current_line and is_message_header(details) then
-      vim.api.nvim_win_set_cursor(win, { line, 0 })
-      return
-    end
+  local previous_message = renderer.get_prev_rendered_message(current_line)
+  if previous_message and previous_message.line_start then
+    vim.api.nvim_win_set_cursor(win, { previous_message.line_start + 1, 0 })
+    return
   end
+
   vim.api.nvim_win_set_cursor(win, { 1, 0 })
 end