fix(term): handle terminal size query failure gracefully

Changes:
- replace assert on ioctl failure with graceful return and user notification in term.lua
- guard against nil TIOCGWINSZ on unsupported OS before calling ioctl
- initialize cached_size as nil instead of all-zero struct to avoid silent division-by-zero
- add nil guards for get_size() in renderer.lua, kitty/init.lua, and document.lua

Refs: #210, #339

Author: 3rd

lua/image/backends/kitty/init.lua

@@ -111,6 +111,7 @@ backend.render = function(image, x, y, width, height)
   -- crop
   if backend.features.crop then
     local term_size = utils.term.get_size()
+    if not term_size then return end
     local pixel_width = width * term_size.cell_width
     local pixel_height = height * term_size.cell_height
     local pixel_top = 0

lua/image/renderer.lua

@@ -19,6 +19,7 @@ local cache = {}
 local render = function(image)
   local state = image.global_state
   local term_size = utils.term.get_size()
+  if not term_size then return end
   local scale_factor = 1.0
   if type(state.options.scale_factor) == "number" then scale_factor = state.options.scale_factor end
   local image_rows = math.floor(image.image_height / term_size.cell_height * scale_factor)

lua/image/utils/document.lua

@@ -114,6 +114,7 @@ local create_document_integration = function(config)
 
             -- Create a floating window for the image
             local term_size = utils.term.get_size()
+            if not term_size then return end
             local width, height = utils.math.adjust_to_aspect_ratio(
               term_size,
               image.image_width,

lua/image/utils/term.lua

@@ -1,11 +1,6 @@
-local cached_size = {
-  screen_x = 0,
-  screen_y = 0,
-  screen_cols = 0,
-  screen_rows = 0,
-  cell_width = 0,
-  cell_height = 0,
-}
+---@type { screen_x: number, screen_y: number, screen_cols: number, screen_rows: number, cell_width: number, cell_height: number }|nil
+local cached_size = nil
+local size_warned = false
 
 -- https://github.com/edluffy/hologram.nvim/blob/main/lua/hologram/state.lua#L15
 local update_size = function()
@@ -29,9 +24,23 @@ local update_size = function()
     TIOCGWINSZ = 0x40087468
   end
 
+  if not TIOCGWINSZ then
+    if not size_warned then
+      size_warned = true
+      vim.notify("image.nvim: unsupported OS — cannot query terminal size", vim.log.levels.WARN)
+    end
+    return
+  end
+
   ---@type { row: number, col: number, xpixel: number, ypixel: number }
   local sz = ffi.new("winsize")
-  assert(ffi.C.ioctl(1, TIOCGWINSZ, sz) == 0, "Failed to get terminal size")
+  if ffi.C.ioctl(1, TIOCGWINSZ, sz) ~= 0 then
+    if not size_warned then
+      size_warned = true
+      vim.notify("image.nvim: cannot query terminal size (non-terminal environment?)", vim.log.levels.WARN)
+    end
+    return
+  end
 
   local xpixel = sz.xpixel
   local ypixel = sz.ypixel