fix: skip pixel model-line alignment on Emacs <29

`string-pixel-width' and `buffer-text-pixel-size' are both Emacs 29+.
Remove dead `buffer-text-pixel-size' branch and skip pixel
right-alignment on 28.x, where `string-width' fallback would push
right segments past the window edge.  Guard pixel-specific tests.

Author: zikajk

eca-chat.el

@@ -2595,15 +2595,10 @@ are in progress."
   "Return the rendered pixel width of STRING for mode-line alignment.
 Honors `display' specs (e.g. the context bar's pixel-width spaces) and
 wide glyphs, unlike `length'.  Uses `string-pixel-width' when
-available, otherwise `buffer-text-pixel-size', falling back to
-`string-width' on Emacsen without either."
+available, falling back to `string-width' on Emacsen without it."
   (cond
    ((string-empty-p string) 0)
    ((fboundp 'string-pixel-width) (string-pixel-width string))
-   ((fboundp 'buffer-text-pixel-size)
-    (with-temp-buffer
-      (insert string)
-      (car (buffer-text-pixel-size nil nil t))))
    (t (string-width string))))
 
 (defun eca-chat--mode-line-string (session)
@@ -2629,7 +2624,8 @@ available, otherwise `buffer-text-pixel-size', falling back to
                              (eca-chat--mode-line-module session m))
                            right-modules))
                     "")))
-           (fill (if (string-empty-p right)
+           (fill (if (or (string-empty-p right)
+                         (not (fboundp 'string-pixel-width)))
                      ""
                    (let ((px (eca-chat--string-pixel-width right)))
                      (propertize

test/eca-chat-test.el

@@ -988,6 +988,8 @@ does not treat the first line as metadata.  Returns FN's value."
     (expect (eca-chat--string-pixel-width "") :to-equal 0))
 
   (it "honors pixel-width display specs instead of counting chars"
+    (unless (fboundp 'string-pixel-width)
+      (buttercup-skip "string-pixel-width not available"))
     ;; A single space carrying a 40px display width must measure ~40, not
     ;; 1 (its `length').  Counting it as 1 char is what pushed the :usage
     ;; and :trust mode-line segments off the right edge once the context
@@ -997,6 +999,8 @@ does not treat the first line as metadata.  Returns FN's value."
       (expect (eca-chat--string-pixel-width s) :to-equal 40)))
 
   (it "measures a pixel context-bar wider than its char length"
+    (unless (fboundp 'string-pixel-width)
+      (buttercup-skip "string-pixel-width not available"))
     (let ((bar (eca-chat--context-bar-pixels
                 (list (list :name "System prompt" :tokens 100 :color "#ff0000"))
                 (list :freeColor "#222222")
@@ -1005,6 +1009,8 @@ does not treat the first line as metadata.  Returns FN's value."
 
 (describe "eca-chat context-bar compaction marker"
   (it "keeps the pixel-bar total width when the marker is overlaid"
+    (unless (fboundp 'string-pixel-width)
+      (buttercup-skip "string-pixel-width not available"))
     (let* ((cats (list (list :name "System prompt" :tokens 100 :color "#ff0000")))
            (bd (list :freeColor "#222222"))
            (plain (eca-chat--context-bar-pixels cats bd 16 0.5))