fix(messages): validate msg_grid before using msg_grid_pos (#26189)

src/nvim/message.c

@@ -2990,10 +2990,13 @@ void msg_clr_eos_force(void)
   int msg_startcol = (cmdmsg_rl) ? 0 : msg_col;
   int msg_endcol = (cmdmsg_rl) ? Columns - msg_col : Columns;
 
+  // TODO(bfredl): ugly, this state should already been validated at this
+  // point. But msg_clr_eos() is called in a lot of places.
   if (msg_grid.chars && msg_row < msg_grid_pos) {
-    // TODO(bfredl): ugly, this state should already been validated at this
-    // point. But msg_clr_eos() is called in a lot of places.
-    msg_row = msg_grid_pos;
+    msg_grid_validate();
+    if (msg_row < msg_grid_pos) {
+      msg_row = msg_grid_pos;
+    }
   }
 
   grid_fill(&msg_grid_adj, msg_row, msg_row + 1, msg_startcol, msg_endcol,

test/functional/ui/messages_spec.lua

@@ -1402,6 +1402,19 @@ vimComment     xxx match /\s"[^\-:.%#=*].*$/ms=s+1,lc=1  excludenl contains=@vim
     ]])
     eq(1, meths.get_option_value('cmdheight', {}))
   end)
+
+  it('using nvim_echo in VimResized does not cause hit-enter prompt #26139', function()
+    command([[au VimResized * lua vim.api.nvim_echo({ { '123456' } }, true, {})]])
+    screen:try_resize(60, 5)
+    screen:expect([[
+      ^                                                            |
+      {1:~                                                           }|
+      {1:~                                                           }|
+      {1:~                                                           }|
+                                                                  |
+    ]])
+    eq({ mode = 'n', blocking = false }, meths.get_mode())
+  end)
 end)
 
 it('calling screenstring() after redrawing between messages without UI #20999', function()