fix(output): set fold fillchars for cleaner fold column rendering

Author: jensenojs

lua/opencode/ui/output_window.lua

@@ -222,6 +222,7 @@ function M.setup(windows)
   window_options.set_window_option('foldenable', true, windows.output_win)
   window_options.set_window_option('foldlevel', 0, windows.output_win)
   window_options.set_window_option('foldcolumn', '1', windows.output_win)
+  window_options.set_window_option('fillchars', 'fold:-,foldopen:-,foldclose:+,foldsep:│', windows.output_win)
   window_options.set_window_option('foldtext', 'v:lua.opencode_fold_text()', windows.output_win)
 
   if config.ui.position ~= 'current' then

tests/unit/output_window_spec.lua

@@ -154,6 +154,14 @@ describe('output_window.setup', function()
     assert.equals(0, foldlevel)
   end)
 
+  it('sets fold fillchars to avoid numeric fold column markers', function()
+    output_window.setup({ output_buf = buf, output_win = win })
+
+    local fillchars = vim.api.nvim_get_option_value('fillchars', { win = win })
+
+    assert.equals('fold:-,foldopen:-,foldclose:+,foldsep:│', fillchars)
+  end)
+
   it('applies closed folds immediately when fold ranges change', function()
     output_window.setup({ output_buf = buf, output_win = win })
     output_window.set_lines({ 'a', 'b', 'c', 'd' })