fix: replace stty size with tput cols/lines in backend-size

stty size returns incomplete data when run through uiop:run-program
(the child may not have terminal access). tput is a terminfo utility
that outputs a single number per call, avoiding parsing issues.
Works reliably in any subprocess context.

src/backend/modern.lisp

@@ -162,25 +162,21 @@ as a fallback when a keyword is not in *named-colors*.")
   (values))
 
 (defmethod backend-size ((b modern-backend))
-  (or       ;; stty size via subprocess — most reliable across all systems.
-      ;; Returns "ROWS COLS". stty size queries the terminal via ioctl,
-      ;; not stdin, so no :input redirection is needed.
+  (or ;; tput lines / tput cols via subprocess — most reliable across
+      ;; all systems. Each outputs a single number. Works in any
+      ;; subprocess context, no parsing complexity.
       (multiple-value-bind (cols rows)
-          (ignore-errors
-            (let* ((out (uiop:run-program '("stty" "size")
-                                          :output :string
-                                          :ignore-error-status t))
-                   (parts (and out (uiop:split-string
-                                     (string-trim '(#\newline #\space) out)))))
-              (when parts
-                (let ((a (parse-integer (first parts) :junk-allowed t))
-                      (b (when (cdr parts) (parse-integer (second parts) :junk-allowed t))))
-                  (if (and a b (> a 0) (> b 0))
-                      ;; stty returns "ROWS COLS"
-                      (values b a)
-                      ;; stty returned only one value — treat as cols
-                      (when (and a (> a 0))
-                        (values a nil)))))))
+          (values
+            (ignore-errors
+              (parse-integer
+                (string-trim '(#\newline #\space)
+                  (uiop:run-program '("tput" "cols") :output :string
+                                    :ignore-error-status t))))
+            (ignore-errors
+              (parse-integer
+                (string-trim '(#\newline #\space)
+                  (uiop:run-program '("tput" "lines") :output :string
+                                    :ignore-error-status t)))))
         (when (and cols rows (> cols 0) (> rows 0))
           (values cols rows)))
       ;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.