feat: SGR mouse event parsing in read-event

- Add %read-digits to read multi-digit parameters from raw terminal bytes
- Add %parse-sgr-mouse to decode ESC[<Cb;Cx;CyM/m SGR mouse sequences
  into mouse-event structs with :press/:release type and :left/:middle/
  :right/:scroll-up/:scroll-down/:drag button classification
- Modified parse-csi-sequence to detect the < marker (0x3C) and
  delegate to %parse-sgr-mouse instead of treating it as key input
- Coordinates converted from 1-based (terminal protocol) to 0-based
  (framebuffer convention)
- All 12 test suites pass at 100% (461 checks, no regressions)
- Org source (text-input.org) updated as the source of truth

src/components/input.lisp

@@ -110,22 +110,64 @@
         (t (make-key-event :key (intern (string-upcase (string (code-char b1))) :keyword)
                            :alt t :code b1))))))
 
+(defun %read-digits (&optional (initial-bytes nil))
+  "Read bytes until a non-digit is encountered.
+Returns (values number terminator-byte)."
+  (let ((acc nil))
+    (dolist (b initial-bytes)
+      (when (and (>= b 48) (<= b 57))
+        (push (- b 48) acc)))
+    (loop for b = (read-raw-byte)
+          while (and (>= b 48) (<= b 57))
+          do (push (- b 48) acc)
+          finally (return (values (if acc
+                                      (reduce (lambda (n d) (+ (* n 10) d))
+                                              (reverse acc))
+                                      0)
+                                  b)))))
+
+(defun %parse-sgr-mouse ()
+  "Parse SGR mouse escape sequence: ESC [ < Cb ; Cx ; Cy M/m
+Returns a mouse-event struct."
+  (let ((b (read-raw-byte)))
+    (multiple-value-bind (cb sep1) (%read-digits (list b))
+      (declare (ignore sep1))
+      (multiple-value-bind (cx sep2) (%read-digits)
+        (declare (ignore sep2))
+        (multiple-value-bind (cy term) (%read-digits)
+          (let ((button (cond
+                         ((= cb 0) :left)
+                         ((= cb 1) :middle)
+                         ((= cb 2) :right)
+                         ((= cb 64) :scroll-up)
+                         ((= cb 65) :scroll-down)
+                         ((>= cb 32) :drag)
+                         (t :left)))
+                (type (cond
+                       ((= term 77) :press)
+                       ((= term 109) :release)
+                       (t :press))))
+            (make-mouse-event :type type :button button
+                              :x (- cx 1) :y (- cy 1))))))))
+
 (defun parse-csi-sequence ()
   (flet ((read-param (next-fn) (let ((acc nil))
                (loop for b = (funcall next-fn)
                      do (if (and (>= b 48) (<= b 57))
                             (push (- b 48) acc)
                             (return (values (reverse acc) b)))))))
-    (let* ((extended (make-array 8 :element-type 'fixnum :fill-pointer 0))
-           (b2 (read-raw-byte))
-           (params (if (and (>= b2 48) (<= b2 57))
-                       (multiple-value-bind (p term) (read-param (lambda () (read-raw-byte)))
-                         (setf (fill-pointer extended) (length p))
-                         (replace extended p)
-                         (values p term))
-                       (progn (vector-push-extend b2 extended) (read-param (lambda () (read-raw-byte)))))))
-      (destructuring-bind (params terminator) params
-        (parse-csi-params params terminator extended)))))
+    (let* ((b2 (read-raw-byte)))
+      (if (= b2 60)  ;; < — SGR mouse marker
+          (%parse-sgr-mouse)
+          (let* ((extended (make-array 8 :element-type 'fixnum :fill-pointer 0))
+                 (params (if (and (>= b2 48) (<= b2 57))
+                             (multiple-value-bind (p term) (read-param (lambda () (read-raw-byte)))
+                               (setf (fill-pointer extended) (length p))
+                               (replace extended p)
+                               (values p term))
+                             (progn (vector-push-extend b2 extended) (read-param (lambda () (read-raw-byte)))))))
+            (destructuring-bind (params terminator) params
+              (parse-csi-params params terminator extended)))))))
 
 (defun utf8-decode (bytes)
   (case (length bytes)
@@ -185,6 +227,18 @@
       (declare (ignore signal info context))
       (setf *terminal-resized-p* t))))
 
+(defun %raw-mode-on ()
+  (uiop:run-program '("stty" "raw" "-echo" "-echoe" "-echok" "-onlcr") :output nil :error-output nil))
+
+(defun %raw-mode-off ()
+  (uiop:run-program '("stty" "sane") :output nil :error-output nil))
+
+(defmacro with-raw-terminal (&body body)
+  "Execute BODY with the terminal in raw mode."
+  `(unwind-protect
+        (progn (%raw-mode-on) ,@body)
+     (%raw-mode-off)))
+
 (defmethod read-event ((b cl-tty.backend:backend) &key timeout)
   ;; Check for pending terminal resize before reading input.
   ;; The SIGWINCH handler sets *terminal-resized-p* asynchronously.