fix: replace stty/tput fallback with direct ioctl on /dev/tty

uiop:run-program can inherit different terminal state than the
interactive shell. Opening /dev/tty directly and calling ioctl
on that fd is equivalent to what the shell's stty does, and
works regardless of SBCL's fd inheritance quirks.

src/backend/simple.lisp

@@ -34,30 +34,20 @@
                  (values (sb-alien:deref winsize 1)
                          (sb-alien:deref winsize 0)))
             (sb-alien:free-alien winsize))))
-      ;; stty size — reliable across all shells and terminals.
+      ;; Direct ioctl on /dev/tty — opens the real controlling terminal.
       (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 (and parts (= (length parts) 2))
-            (let ((rows (parse-integer (first parts) :junk-allowed t))
-                  (cols (parse-integer (second parts) :junk-allowed t)))
-              (when (and rows cols (> rows 0) (> cols 0))
-                (values cols rows))))))
-      ;; tput — final shell fallback
-      (ignore-errors
-        (let* ((out (uiop:run-program '("sh" "-c" "tput cols 2>/dev/null; tput lines 2>/dev/null")
-                                       :output :string
-                                       :ignore-error-status t))
-               (parts (and out (uiop:split-string
-                                 (string-trim '(#\newline #\space) out)))))
-          (when (and parts (= (length parts) 2))
-            (let ((cols (parse-integer (first parts) :junk-allowed t))
-                  (rows (parse-integer (second parts) :junk-allowed t)))
-              (when (and rows cols (> rows 0) (> cols 0))
-                (values cols rows))))))
+        (let ((tty-fd (sb-unix:unix-open "/dev/tty" sb-unix:o-rdwr 0)))
+          (when tty-fd
+            (unwind-protect
+                 (let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+                   (sb-unix:unix-ioctl tty-fd 21523 (sb-alien:alien-sap winsize))
+                   (let ((cols (sb-alien:deref winsize 1))
+                         (rows (sb-alien:deref winsize 0)))
+                     (sb-alien:free-alien winsize)
+                     (when (and (integerp cols) (integerp rows)
+                                (> cols 0) (> rows 0))
+                       (values cols rows))))
+              (sb-unix:unix-close tty-fd)))))
       (values 80 24)))
 
 (defmethod backend-write ((b simple-backend) string)