fix: use :input :interactive for stty size subprocess

SBCL's stdin during --load is the load file, NOT the terminal.
When uiop:run-program creates a subprocess, it inherits this
stdin, so 'stty size' reads from the load file and fails.
:input :interactive opens /dev/tty for the child's stdin,
matching the behavior of 'stty size' from an interactive shell.

src/backend/modern.lisp

@@ -163,20 +163,29 @@ as a fallback when a keyword is not in *named-colors*.")
 
 (defmethod backend-size ((b modern-backend))
   (or       ;; stty size via subprocess — most reliable across all systems.
-      ;; Returns "ROWS COLS". Uses explicit /dev/tty to bypass any
+      ;; Returns "ROWS COLS". Uses :input :interactive so the subprocess
-      ;; stdin redirection from uiop:run-program.
+      ;; opens /dev/tty for its stdin (SBCL's stdin is the load file).
+      (multiple-value-bind (cols rows)
           (ignore-errors
-        (let* ((out (uiop:run-program '("sh" "-c" "stty size < /dev/tty")
+            (let* ((out (uiop:run-program '("stty" "size")
                                           :output :string
+                                          :input :interactive
                                           :ignore-error-status t))
                    (parts (and out (uiop:split-string
                                      (string-trim '(#\newline #\space) out)))))
-          (when (and parts (= (length parts) 2))
+              (when parts
-            (let ((rows (parse-integer (first parts) :junk-allowed t))
+                (let ((a (parse-integer (first parts) :junk-allowed t))
-                  (cols (parse-integer (second parts) :junk-allowed t)))
+                      (b (when (cdr parts) (parse-integer (second parts) :junk-allowed t))))
-              (when (and rows cols (> rows 0) (> cols 0))
+                  (if (and a b (> a 0) (> b 0))
-                (values cols rows))))))
+                      ;; stty returns "ROWS COLS"
+                      (values b a)
+                      ;; stty returned only one value — treat as cols
+                      (when (and a (> a 0))
+                        (values a nil)))))))
+        (when (and cols rows (> cols 0) (> rows 0))
+          (values cols rows)))
       ;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.
+      (multiple-value-bind (cols rows)
           (ignore-errors
             (let* ((+tiocgwinsz+ 21523)  ; 0x5413 on Linux
                    (winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
@@ -188,6 +197,8 @@ as a fallback when a keyword is not in *named-colors*.")
                      (values (sb-alien:deref winsize 1)  ;; cols
                              (sb-alien:deref winsize 0))) ;; rows
                 (sb-alien:free-alien winsize))))
+        (when (and cols rows (> cols 0) (> rows 0))
+          (values cols rows)))
       ;; Direct ioctl on /dev/tty — opens the real controlling terminal.
       (ignore-errors
         (let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))  ; O_RDONLY

src/backend/simple.lisp

@@ -23,39 +23,24 @@
 
 (defmethod backend-size ((b simple-backend))
   (or ;; stty size via subprocess — most reliable across all systems.
+      (multiple-value-bind (cols rows)
           (ignore-errors
-        (let* ((out (uiop:run-program '("sh" "-c" "stty size < /dev/tty")
+            (let* ((out (uiop:run-program '("stty" "size")
                                           :output :string
+                                          :input :interactive
                                           :ignore-error-status t))
                    (parts (and out (uiop:split-string
                                      (string-trim '(#\newline #\space) out)))))
-          (when (and parts (= (length parts) 2))
+              (when parts
-            (let ((rows (parse-integer (first parts) :junk-allowed t))
+                (let ((a (parse-integer (first parts) :junk-allowed t))
-                  (cols (parse-integer (second parts) :junk-allowed t)))
+                      (b (when (cdr parts) (parse-integer (second parts) :junk-allowed t))))
-              (when (and rows cols (> rows 0) (> cols 0))
+                  (if (and a b (> a 0) (> b 0))
-                (values cols rows))))))
+                      (values b a)   ; stty returns "ROWS COLS"
-      (ignore-errors
+                      (when (and a (> a 0))
-        (let* ((+tiocgwinsz+ 21523)
+                        (values a nil)))))))
-               (winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+        (when (and cols rows (> cols 0) (> rows 0))
-          (unwind-protect
+          (values cols rows)))
-               (progn
+      (multiple-value-bind (cols rows)
-                 (sb-unix:unix-ioctl (sb-sys:fd-stream-fd
-                                      (backend-output-stream b))
-                                     +tiocgwinsz+
-                                     (sb-alien:alien-sap winsize))
-                 (values (sb-alien:deref winsize 1)
-                         (sb-alien:deref winsize 0)))
-             (sb-alien:free-alien winsize))))
-      ;; stty size via subprocess — reliable on every Unix.
-      (ignore-errors
-        (let* ((out (uiop:run-program '("sh" "-c" "stty size < /dev/tty")
-                                      :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))))))
       (ignore-errors