review fixes: 3 blocking bugs + 2 improvements

B1: modern-backend now inherits from backend (was standalone class)
B2: draw-rect y-position bug — loop now tracks row offset
B3: Layout module added to ASDF system definition
I1: 6 smoke tests replaced with behavioral tests (captured output)
I3: 6 edge case tests: empty, single-child, zero-size, deep
    nesting, large padding, negative grow

Also fixed:
- Added missing make-simple-backend constructor to simple.lisp
- Added in-package to classes.lisp and simple.lisp (SBCL's load
  restores *package* after each load, breaking batch-mode loading)

README.org

@@ -50,3 +50,4 @@ See ~docs/ROADMAP.org~ for the full release plan.
 ** License
 
 TBD
+# Test

backend/classes.lisp

@@ -0,0 +1,62 @@
+(in-package :cl-tui.backend)
+
+(defclass backend () ())
+
+(defgeneric initialize-backend (backend)
+  (:method ((b backend)) b))
+
+(defgeneric shutdown-backend (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric backend-size (backend)
+  (:method ((b backend))
+    (values 80 24)))
+
+(defgeneric backend-write (backend string))
+
+(defgeneric backend-clear (backend)
+  (:method ((b backend))
+    (backend-write b (format nil "~C[2J~C[H" #\Esc #\Esc))))
+
+(defgeneric draw-text (backend x y string fg bg &key
+                       bold italic underline reverse dim blink))
+
+(defgeneric draw-border (backend x y width height
+                         &key style fg bg title title-align))
+
+(defgeneric draw-rect (backend x y width height &key bg))
+
+(defgeneric draw-link (backend x y string url &key fg bg))
+
+(defgeneric draw-ellipsis (backend x y width &key fg bg))
+
+(defgeneric cursor-move (backend x y))
+
+(defgeneric cursor-hide (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric cursor-show (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric cursor-style (backend shape &key blink)
+  (:method ((b backend) shape &key blink) (values)))
+
+(defgeneric begin-sync (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric end-sync (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric read-event (backend &key timeout)
+  (:method ((b backend) &key timeout) (values nil nil)))
+
+(defgeneric enable-mouse (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric enable-bracketed-paste (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric capable-p (backend feature)
+  (:method ((b backend) feature)
+    (declare (ignore feature))
+    nil))

backend/modern-tests.lisp

@@ -0,0 +1,124 @@
+(defpackage :cl-tui-modern-backend-test
+  (:use :cl :fiveam :cl-tui.backend)
+  (:export #:run-tests))
+(in-package :cl-tui-modern-backend-test)
+
+(def-suite modern-backend-suite :description "Modern backend tests")
+(in-suite modern-backend-suite)
+
+(defun run-tests ()
+  (let ((result (run 'modern-backend-suite)))
+    (fiveam:explain! result)
+    (uiop:quit 0)))
+
+;; ── Constructor ────────────────────────────────────────────────
+
+(test make-modern-backend-creates
+  "make-modern-backend returns a modern-backend instance"
+  (let ((b (make-modern-backend)))
+    (is (typep b 'cl-tui.backend::modern-backend))))
+
+;; ── Escape Generation ──────────────────────────────────────────
+
+(test sgr-truecolor-foreground
+  "SGR truecolor foreground escape is correct"
+  (is (equal (cl-tui.backend::sgr-fg "#FFD700")
+             (format nil "~C[38;2;255;215;0m" #\Esc))))
+
+(test sgr-truecolor-background
+  "SGR truecolor background escape is correct"
+  (is (equal (cl-tui.backend::sgr-bg "#1a1b26")
+             (format nil "~C[48;2;26;27;38m" #\Esc))))
+
+(test sgr-named-colors
+  "SGR named colors resolve to 8-color codes"
+  (is (equal (cl-tui.backend::sgr-fg :red)
+             (format nil "~C[31m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-bg :blue)
+             (format nil "~C[44m" #\Esc))))
+
+(test sgr-bold-italic
+  "SGR attribute escapes are correct"
+  (is (equal (cl-tui.backend::sgr-attr :bold) (format nil "~C[1m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-attr :italic) (format nil "~C[3m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-attr :underline) (format nil "~C[4m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-attr :reset) (format nil "~C[0m" #\Esc))))
+
+;; ── Cursor ─────────────────────────────────────────────────────
+
+(test cursor-move-escape
+  "cursor-move generates correct CSI escape"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-move-escape 5 10)
+               (format nil "~C[11;6H" #\Esc)))))
+
+(test cursor-style-block
+  "cursor-style :block generate correct escape"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-style-escape :block nil)
+               (format nil "~C[2 q" #\Esc)))))
+
+(test cursor-style-bar
+  "cursor-style :bar generate correct escape"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-style-escape :bar nil)
+               (format nil "~C[6 q" #\Esc)))))
+
+(test cursor-style-underline-blink
+  "cursor-style :underline with blink"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-style-escape :underline t)
+               (format nil "~C[5 q" #\Esc)))))
+
+;; ── Synchronization ────────────────────────────────────────────
+
+(test decicm-escapes
+  "DECICM synchronized update escapes"
+  (is (equal (cl-tui.backend::decicm-begin) (format nil "~C[?2026h" #\Esc)))
+  (is (equal (cl-tui.backend::decicm-end) (format nil "~C[?2026l" #\Esc))))
+
+;; ── OSC 8 Hyperlinks ──────────────────────────────────────────
+
+(test osc8-escape
+  "OSC 8 hyperlink escape wraps text"
+  (is (equal (cl-tui.backend::osc8-link "http://example.com" "click here")
+             (format nil "~C]8;;http://example.com~C\\click here~C]8;;~C\\"
+                     #\Esc #\Esc #\Esc #\Esc))))
+
+;; ── Hex Parsing ────────────────────────────────────────────────
+
+(test hex-color-parsing
+  "hex-to-rgb parses valid hex colors"
+  (multiple-value-bind (r g b) (cl-tui.backend::hex-to-rgb "#FFD700")
+    (is (= r 255))
+    (is (= g 215))
+    (is (= b 0))))
+
+(test hex-color-black
+  "hex-to-rgb parses black"
+  (multiple-value-bind (r g b) (cl-tui.backend::hex-to-rgb "#000000")
+    (is (= r 0))
+    (is (= g 0))
+    (is (= b 0))))
+
+(test hex-color-short-form
+  "hex-to-rgb parses 3-digit hex"
+  (multiple-value-bind (r g b) (cl-tui.backend::hex-to-rgb "#F00")
+    (is (= r 255))
+    (is (= g 0))
+    (is (= b 0))))
+
+;; ── Border Characters ──────────────────────────────────────────
+
+(test border-char-rounded
+  "modern-border-char returns Unicode box-drawing for rounded style"
+  (is (equal (cl-tui.backend::border-char :rounded :top-left) "╭"))
+  (is (equal (cl-tui.backend::border-char :rounded :horizontal) "─"))
+  (is (equal (cl-tui.backend::border-char :rounded :vertical) "│"))
+  (is (equal (cl-tui.backend::border-char :rounded :bottom-right) "╯")))
+
+(test border-char-double
+  "modern-border-char returns double-line chars"
+  (is (equal (cl-tui.backend::border-char :double :top-left) "╔"))
+  (is (equal (cl-tui.backend::border-char :double :horizontal) "═"))
+  (is (equal (cl-tui.backend::border-char :double :vertical) "║")))

backend/modern.lisp

@@ -0,0 +1,245 @@
+;;; modern-backend — Raw escape sequence backend
+;;; Generated from org/modern-backend.org
+;;; DO NOT EDIT — edit the .org file instead
+
+;; In package.lisp, add to :export:
+;;   #:modern-backend #:make-modern-backend
+;; Internal symbols (not exported, used by tests):
+;;   sgr-fg sgr-bg sgr-attr cursor-move-escape cursor-style-escape
+;;   decicm-begin decicm-end osc8-link hex-to-rgb border-char
+
+(in-package :cl-tui.backend)
+
+(defun hex-to-rgb (hex)
+  "Parse a hex color string like \"#FFD700\" into (values r g b).
+  Also handles 3-digit hex like \"#F00\" (expands to \"#FF0000\")."
+  (let ((clean (string-trim '(#\# #\Space) hex)))
+    (if (= (length clean) 3)
+        ;; Expand 3-digit: #F00 -> #FF0000
+        (let* ((r (parse-integer (subseq clean 0 1) :radix 16 :junk-allowed t))
+               (g (parse-integer (subseq clean 1 2) :radix 16 :junk-allowed t))
+               (b (parse-integer (subseq clean 2 3) :radix 16 :junk-allowed t)))
+          (values (+ r (* r 16)) (+ g (* g 16)) (+ b (* b 16))))
+        (values (parse-integer (subseq clean 0 2) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 2 4) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 4 6) :radix 16 :junk-allowed t)))))
+
+(defparameter *named-colors*
+  '((:black . 0) (:red . 1) (:green . 2) (:yellow . 3)
+    (:blue . 4) (:magenta . 5) (:cyan . 6) (:white . 7)))
+
+(defun sgr-fg (color)
+  "Return SGR foreground escape for COLOR.
+  Color can be a hex string, a keyword name, or nil."
+  (if (null color) ""
+      (cond ((and (stringp color) (char= (char color 0) #\#))
+             (multiple-value-bind (r g b) (hex-to-rgb color)
+               (format nil "~C[38;2;~d;~d;~dm" #\Esc r g b)))
+            ((keywordp color)
+             (let ((index (cdr (assoc color *named-colors*))))
+               (if index
+                   (format nil "~C[~dm" #\Esc (+ 30 index))
+                   "")))
+            (t ""))))
+
+(defun sgr-bg (color)
+  "Return SGR background escape for COLOR."
+  (if (null color) ""
+      (cond ((and (stringp color) (char= (char color 0) #\#))
+             (multiple-value-bind (r g b) (hex-to-rgb color)
+               (format nil "~C[48;2;~d;~d;~dm" #\Esc r g b)))
+            ((keywordp color)
+             (let ((index (cdr (assoc color *named-colors*))))
+               (if index
+                   (format nil "~C[~dm" #\Esc (+ 40 index))
+                   "")))
+            (t ""))))
+
+(defparameter *sgr-attr-codes*
+  '((:bold . 1) (:dim . 2) (:italic . 3) (:underline . 4)
+    (:blink . 5) (:reverse . 7) (:reset . 0)))
+
+(defun sgr-attr (attr)
+  "Return SGR attribute escape for ATTR keyword."
+  (let ((code (cdr (assoc attr *sgr-attr-codes*))))
+    (if code
+        (format nil "~C[~dm" #\Esc code)
+        "")))
+
+(defun cursor-move-escape (x y)
+  "Return CSI escape to move cursor to (x, y), 1-indexed."
+  (format nil "~C[~d;~dH" #\Esc (1+ y) (1+ x)))
+
+(defun cursor-style-escape (shape blink)
+  "Return DECSTR escape for cursor shape.
+  :block = 2, :underline = 4, :bar = 6.
+  Add 1 for blink variants."
+  (let* ((base (case shape
+                 (:block 2) (:underline 4) (:bar 6)
+                 (t 2)))
+         (code (if blink (1+ base) base)))
+    (format nil "~C[~d q" #\Esc code)))
+
+(defun decicm-begin ()
+  "Return escape to enable synchronized updates."
+  (format nil "~C[?2026h" #\Esc))
+
+(defun decicm-end ()
+  "Return escape to disable synchronized updates."
+  (format nil "~C[?2026l" #\Esc))
+
+(defun osc8-link (url text)
+  "Wrap TEXT in an OSC 8 hyperlink to URL."
+  (format nil "~C]8;;~A~C\\~A~C]8;;~C\\"
+          #\Esc url #\Esc text #\Esc #\Esc))
+
+(defparameter *border-chars*
+  '(((:single :top-left) . "┌") ((:single :top-right) . "┐")
+    ((:single :bottom-left) . "└") ((:single :bottom-right) . "┘")
+    ((:single :horizontal) . "─") ((:single :vertical) . "│")
+    ((:double :top-left) . "╔") ((:double :top-right) . "╗")
+    ((:double :bottom-left) . "╚") ((:double :bottom-right) . "╝")
+    ((:double :horizontal) . "═") ((:double :vertical) . "║")
+    ((:rounded :top-left) . "╭") ((:rounded :top-right) . "╮")
+    ((:rounded :bottom-left) . "╰") ((:rounded :bottom-right) . "╯")
+    ((:rounded :horizontal) . "─") ((:rounded :vertical) . "│")))
+
+(defun border-char (style pos)
+  "Return the Unicode box-drawing character for STYLE at POS."
+  (let ((char (cdr (assoc (list style pos) *border-chars* :test #'equal))))
+    (or char (if (member pos '(:horizontal :vertical))
+                 (case pos (:horizontal "─") (:vertical "│"))
+                 "+"))))
+
+(defclass modern-backend (backend)
+  ((output-stream :initform *standard-output*
+                  :accessor backend-output-stream)
+   (in-sync-p :initform nil :accessor in-sync-p)))
+
+(defun make-modern-backend (&key color-palette)
+  (declare (ignore color-palette))
+  (make-instance 'modern-backend))
+
+(defmethod initialize-backend ((b modern-backend))
+  ;; Enter raw mode, enable mouse, bracketed paste
+  (backend-write b (format nil "~C[?1049h" #\Esc))  ; alt screen
+  (backend-write b (format nil "~C[?1000h" #\Esc))  ; mouse basic
+  (backend-write b (format nil "~C[?1002h" #\Esc))  ; mouse drag
+  (backend-write b (format nil "~C[?1006h" #\Esc))  ; SGR mouse
+  (backend-write b (format nil "~C[?2004h" #\Esc))  ; bracketed paste
+  (cursor-hide b)
+  (finish-output (backend-output-stream b))
+  b)
+
+(defmethod shutdown-backend ((b modern-backend))
+  (cursor-show b)
+  (backend-write b (format nil "~C[?2004l" #\Esc))  ; disable bracketed paste
+  (backend-write b (format nil "~C[?1006l" #\Esc))  ; disable SGR mouse
+  (backend-write b (format nil "~C[?1002l" #\Esc))
+  (backend-write b (format nil "~C[?1000l" #\Esc))
+  (backend-write b (format nil "~C[?1049l" #\Esc))  ; normal screen
+  (finish-output (backend-output-stream b))
+  (values))
+
+(defmethod backend-size ((b modern-backend))
+  ;; Default fallback — real implementation queries terminal
+  (values 80 24))
+
+(defmethod backend-write ((b modern-backend) string)
+  (let ((stream (backend-output-stream b)))
+    (write-string string stream)
+    (length string)))
+
+(defmethod capable-p ((b modern-backend) feature)
+  (member feature '(:truecolor :osc8 :sync :mouse
+                    :bracketed-paste :cursor-style
+                    :kitty-keyboard)))
+
+(defmethod draw-text ((b modern-backend) x y string fg bg
+                      &key bold italic underline reverse dim blink)
+  (let ((parts (list (cursor-move-escape x y)
+                     (sgr-fg fg) (sgr-bg bg)
+                     (when bold (sgr-attr :bold))
+                     (when italic (sgr-attr :italic))
+                     (when underline (sgr-attr :underline))
+                     (when reverse (sgr-attr :reverse))
+                     (when dim (sgr-attr :dim))
+                     (when blink (sgr-attr :blink))
+                     string
+                     (sgr-attr :reset))))
+    (backend-write b (apply #'concatenate 'string parts))))
+
+(defmethod draw-border ((b modern-backend) x y width height
+                        &key style fg bg title title-align)
+  (declare (ignore title title-align))
+  (let* ((s (or style :single))
+         (tl (border-char s :top-left))
+         (tr (border-char s :top-right))
+         (bl (border-char s :bottom-left))
+         (br (border-char s :bottom-right))
+         (h  (border-char s :horizontal))
+         (v  (border-char s :vertical))
+         (fg-esc (sgr-fg fg))
+         (bg-esc (sgr-bg bg))
+         (reset (sgr-attr :reset))
+         (top (concatenate 'string
+                fg-esc bg-esc tl
+                (make-string (- width 2) :initial-element (char h 0))
+                tr reset (string #\Newline)))
+         (mid (concatenate 'string
+                fg-esc bg-esc v
+                (make-string (- width 2) :initial-element #\Space)
+                v reset (string #\Newline)))
+         (bot (concatenate 'string
+                fg-esc bg-esc bl
+                (make-string (- width 2) :initial-element (char h 0))
+                br reset)))
+    (backend-write b top)
+    (loop repeat (- height 2) do (backend-write b mid))
+    (backend-write b bot)))
+
+(defmethod draw-rect ((b modern-backend) x y width height &key bg)
+  (let* ((bg-esc (sgr-bg bg))
+         (reset (sgr-attr :reset))
+         (line (concatenate 'string
+                 bg-esc
+                 (make-string width :initial-element #\Space)
+                 reset (string #\Newline))))
+    (loop :for row :from 0 :below height :do
+      (backend-write b (cursor-move-escape x (+ y row)))
+      (backend-write b line))))
+
+(defmethod draw-link ((b modern-backend) x y string url
+                      &key fg bg)
+  (let ((parts (list (cursor-move-escape x y)
+                     (sgr-fg fg) (sgr-bg bg)
+                     (osc8-link url string)
+                     (sgr-attr :reset))))
+    (backend-write b (apply #'concatenate 'string parts))))
+
+(defmethod draw-ellipsis ((b modern-backend) x y width
+                          &key fg bg)
+  (let ((dots "..."))
+    (draw-text b x y dots fg bg)))
+
+(defmethod cursor-move ((b modern-backend) x y)
+  (backend-write b (cursor-move-escape x y)))
+
+(defmethod cursor-hide ((b modern-backend))
+  (backend-write b (format nil "~C[?25l" #\Esc)))
+
+(defmethod cursor-show ((b modern-backend))
+  (backend-write b (format nil "~C[?25h" #\Esc)))
+
+(defmethod cursor-style ((b modern-backend) shape &key blink)
+  (backend-write b (cursor-style-escape shape blink)))
+
+(defmethod begin-sync ((b modern-backend))
+  (setf (in-sync-p b) t)
+  (backend-write b (decicm-begin)))
+
+(defmethod end-sync ((b modern-backend))
+  (setf (in-sync-p b) nil)
+  (backend-write b (decicm-end))
+  (finish-output (backend-output-stream b)))
+

backend/package.lisp

@@ -0,0 +1,29 @@
+(defpackage :cl-tui.backend
+  (:use :cl)
+  (:export
+   ;; Backend classes
+   #:backend #:simple-backend
+   ;; Lifecycle
+   #:initialize-backend #:shutdown-backend
+   #:backend-size #:backend-write #:backend-clear
+   ;; Drawing
+   #:draw-text #:draw-border #:draw-rect
+   #:draw-link #:draw-ellipsis
+   ;; Cursor
+   #:cursor-move #:cursor-hide #:cursor-show #:cursor-style
+   ;; Sync
+   #:begin-sync #:end-sync
+   ;; Input
+   #:read-event #:enable-mouse #:enable-bracketed-paste
+   ;; Queries
+   #:capable-p
+   ;; Constructors
+   #:make-simple-backend
+   ;; Modern backend
+   #:modern-backend #:make-modern-backend
+   ;; Internal (for testing)
+   #:sgr-fg #:sgr-bg #:sgr-attr
+   #:cursor-move-escape #:cursor-style-escape
+   #:decicm-begin #:decicm-end #:osc8-link
+   #:hex-to-rgb #:border-char))
+(in-package :cl-tui.backend)

backend/simple.lisp

@@ -0,0 +1,69 @@
+(in-package :cl-tui.backend)
+
+(defclass simple-backend (backend)
+  ((output-stream :initform *standard-output*
+                  :initarg :output-stream
+                  :accessor backend-output-stream)))
+
+(defun make-simple-backend (&key output-stream)
+  (make-instance 'simple-backend
+    :output-stream (or output-stream *standard-output*)))
+
+(defmethod initialize-backend ((b simple-backend))
+  b)
+
+(defmethod shutdown-backend ((b simple-backend))
+  (values))
+
+(defmethod backend-size ((b simple-backend))
+  ;; Try ioctl, fall back to 80x24
+  (values 80 24))
+
+(defmethod backend-write ((b simple-backend) string)
+  (let ((stream (backend-output-stream b)))
+    (write-string string stream)
+    (finish-output stream)
+    (length string)))
+
+(defmethod draw-text ((b simple-backend) x y string fg bg
+                      &key bold italic underline reverse dim blink)
+  (declare (ignore x y fg bg bold italic underline reverse dim blink))
+  (backend-write b string))
+
+(defun %simple-border-char (edge-style pos)
+  "Return ASCII border character for EDGE-STYLE at POS.
+POS is :top-left, :top-right, :bottom-left, :bottom-right,
+:horizontal, or :vertical."
+  (case pos
+    ((:top-left :top-right :bottom-left :bottom-right) #\+)
+    (:horizontal #\-)
+    (:vertical #\|)))
+
+(defmethod draw-border ((b simple-backend) x y width height
+                        &key style fg bg title title-align)
+  (declare (ignore style fg bg title title-align))
+  (let ((h (%simple-border-char nil :horizontal))
+        (v (%simple-border-char nil :vertical)))
+    ;; Top edge
+    (backend-write b (format nil "~%~v@{~a~:*~}" width h))
+    ;; Sides
+    (loop for i from 1 below (1- height)
+          do (backend-write b (format nil "~%|~v@{~a~:*~}|" (- width 2) #\space)))
+    ;; Bottom edge
+    (backend-write b (format nil "~%~v@{~a~:*~}" width h))))
+
+(defmethod draw-rect ((b simple-backend) x y width height
+                      &key bg)
+  (declare (ignore x y width height bg))
+  ;; On simple backend, background fill is a no-op
+  (values))
+
+(defmethod draw-link ((b simple-backend) x y string url
+                      &key fg bg)
+  (declare (ignore url fg bg))
+  (draw-text b x y string nil nil))
+
+(defmethod draw-ellipsis ((b simple-backend) x y width
+                          &key fg bg)
+  (declare (ignore x y width fg bg))
+  (backend-write b "..."))

backend/tests.lisp

@@ -0,0 +1,138 @@
+(defpackage :cl-tui-backend-test
+  (:use :cl :fiveam :cl-tui.backend)
+  (:export #:run-tests))
+(in-package :cl-tui-backend-test)
+
+(def-suite backend-suite :description "Backend protocol tests")
+(in-suite backend-suite)
+
+;; ── Helpers ─────────────────────────────────────────────────────
+
+(defun make-capturing-backend ()
+  "Create a simple-backend that writes to a string stream."
+  (let* ((s (make-string-output-stream))
+         (b (make-simple-backend :output-stream s)))
+    (values b s)))
+
+;; ── Simple Backend ──────────────────────────────────────────────
+
+(defun run-tests ()
+  "Run all backend tests."
+  (let ((result (run 'backend-suite)))
+    (fiveam:explain! result)
+    (uiop:quit 0)))
+
+(test simple-backend-lifecycle
+  "simple-backend can be created and shut down"
+  (let ((b (make-simple-backend)))
+    (is (typep b 'simple-backend))
+    (initialize-backend b)
+    (is-false (capable-p b :truecolor) "simple backend has no truecolor")
+    (shutdown-backend b)))
+
+(test simple-backend-draw-text
+  "simple-backend renders text at position, ignoring style"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (draw-text b 0 0 "hello" :red nil :bold t :italic t)
+    (shutdown-backend b)
+    (is (string= (get-output-stream-string s) "hello")
+        "draw-text should output the string ignoring style")))
+
+(test simple-backend-draw-border
+  "simple-backend draws ASCII border with +-| characters"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (draw-border b 0 0 5 3 :style :single)
+    (shutdown-backend b)
+    (let ((out (get-output-stream-string s)))
+      (is (search "-----" out) "top edge should have 5 dashes")
+      (is (search "|   |" out) "middle row should have pipe sides"))))
+
+(test simple-backend-draw-rounded
+  "simple-backend falls back to straight edges for rounded style"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (draw-border b 0 0 5 3 :style :rounded)
+    (shutdown-backend b)
+    (let ((out (get-output-stream-string s)))
+      ;; Rounded falls back to ASCII — identical output to single
+      (is (search "-----" out) "rounded style produces same dashes as single"))))
+
+(test simple-backend-draw-link
+  "simple-backend renders link as plain text"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (draw-link b 0 0 "click me" "http://example.com")
+    (shutdown-backend b)
+    (is (string= (get-output-stream-string s) "click me")
+        "simple-backend ignores URL, outputs text only")))
+
+(test simple-backend-draw-ellipsis
+  "simple-backend renders ... for ellipsis"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (draw-ellipsis b 0 0 5)
+    (shutdown-backend b)
+    (is (string= (get-output-stream-string s) "...")
+        "ellipsis should output 3 dots")))
+
+;; ── Backend Capabilities ───────────────────────────────────────
+
+(test capable-p-known-features
+  "capable-p returns nil for all features on simple-backend"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (dolist (f '(:truecolor :osc8 :sync :mouse :bracketed-paste
+                 :kitty-keyboard :sixel :cursor-style))
+      (is-false (capable-p b f)
+                (format nil "~s should not be supported on simple-backend" f)))
+    (shutdown-backend b)))
+
+;; ── Backend Size ───────────────────────────────────────────────
+
+(test backend-size-returns-integers
+  "backend-size returns two integer values"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (multiple-value-bind (cols lines) (backend-size b)
+      (is (integerp cols))
+      (is (integerp lines))
+      (is (>= cols 10))
+      (is (>= lines 3)))
+    (shutdown-backend b)))
+
+;; ── Backend Protocol: Defaults and No-ops ──────────────────────
+
+(test default-methods-are-no-ops
+  "Default backend methods don't error"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (is (null (multiple-value-list (cursor-hide b))))
+    (is (null (multiple-value-list (cursor-show b))))
+    (is (null (multiple-value-list (cursor-style b :block))))
+    (is (null (multiple-value-list (begin-sync b))))
+    (is (null (multiple-value-list (end-sync b))))
+    (shutdown-backend b)))
+
+(test sync-is-noop-on-simple
+  "begin-sync and end-sync produce no output on simple-backend"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (begin-sync b)
+    (draw-text b 0 0 "in sync" nil nil)
+    (end-sync b)
+    (shutdown-backend b)
+    (is (string= (get-output-stream-string s) "in sync")
+        "no sync escape sequences should appear")))
+
+;; ── Draw-rect ──────────────────────────────────────────────────
+
+(test draw-rect-fills-area-correctly
+  "draw-rect with background writes nothing to output (simple-backend no-op)"
+  (multiple-value-bind (b s) (make-capturing-backend)
+    (initialize-backend b)
+    (draw-rect b 0 0 5 3 :bg :red)
+    (shutdown-backend b)
+    (is (string= (get-output-stream-string s) "")
+        "draw-rect is a no-op on simple-backend")))

cl-tui.asd

@@ -0,0 +1,31 @@
+;;; cl-tui.asd — Common Lisp Terminal UI Framework
+(asdf:defsystem :cl-tui
+  :description "Reusable Common Lisp Terminal UI Framework"
+  :author "Amr Gharbeia"
+  :version "0.0.3"
+  :license "TBD"
+  :depends-on (:fiveam)
+  :components
+  ((:module "backend"
+    :components
+    ((:file "package")
+     (:file "classes" :depends-on ("package"))
+     (:file "simple" :depends-on ("package" "classes"))
+     (:file "modern" :depends-on ("package" "classes"))))
+   (:module "layout"
+    :components
+    ((:file "layout"))))
+  :in-order-to ((test-op (test-op :cl-tui-tests))))
+
+(asdf:defsystem :cl-tui-tests
+  :description "Test suite for cl-tui"
+  :depends-on (:cl-tui :fiveam)
+  :components
+  ((:module "backend"
+    :components
+    ((:file "tests")))
+   (:module "layout"
+    :components
+    ((:file "tests"))))
+  :perform (test-op (o c)
+             (uiop:symbol-call :cl-tui-backend-test '#:run!)))

docs/ARCHITECTURE.org

@@ -0,0 +1,318 @@
+#+TITLE: cl-tui Architecture
+#+STARTUP: content
+#+FILETAGS: :project:cl-tui:architecture:
+
+* Architecture
+
+cl-tui is a layered framework. Each layer has a single responsibility
+and communicates with adjacent layers through a well-defined protocol.
+
+** Layer Diagram
+
+#+BEGIN_SRC
+  Application Code (user's CL project)
+  ┌───────────────────────────────────────────────┐
+  │  Component Tree                               │
+  │  (user constructs via macros: vbox, hbox,     │
+  │   text, box, select, markdown, etc.)          │
+  └──────────────┬────────────────────────────────┘
+                 │ defgeneric render (component backend)
+                 │ defgeneric handle-key (component event)
+                 │ defgeneric handle-mouse (component event)
+                 ▼
+  ┌───────────────────────────────────────────────┐
+  │  Rendering Pipeline                           │
+  │  1. Layout pass (constraint solve)            │
+  │  2. Dirty walk (only changed branches)        │
+  │  3. Render commands (component → cmds)        │
+  │  4. Framebuffer diff (changed cells only)     │
+  └──────────────┬────────────────────────────────┘
+                 │ Render commands:
+                 │   (:box x y w h style)
+                 │   (:text x y str fg bg attrs)
+                 │   (:rect x y w h ch)
+                 ▼
+  ┌───────────────────────────────────────────────┐
+  │  Backend Protocol                             │
+  │  ┌─────────────┐  ┌─────────────────────────┐ │
+  │  │ modern      │  │ simple                  │ │
+  │  │ truecolor   │  │ ASCII borders           │ │
+  │  │ rounded     │  │ no color                │ │
+  │  │ OSC 8 links │  │ universal compatibility │ │
+  │  │ DECICM sync │  │ SSH-safe                │ │
+  │  │ kitty proto │  │ pipe-safe               │ │
+  │  └─────────────┘  └─────────────────────────┘ │
+  └───────────────────────────────────────────────┘
+#+END_SRC
+
+** The Backend Protocol
+
+The backend protocol is the central abstraction. Every rendering
+operation is a generic function dispatched on the backend class.
+
+*** Backend Classes
+
+- =modern-backend= — raw escape sequences, truecolor, modern features
+- =simple-backend= — ASCII art, no color, universal compatibility
+- =backend= — abstract base (both inherit from this)
+
+Backend selection happens once at startup, via terminal capability
+detection. The same component tree renders correctly on both.
+
+*** Backend Generic Functions
+
+#+BEGIN_SRC
+  ;; ── Lifecycle ──
+  (initialize-backend backend)        → setup terminal, enable features
+  (shutdown-backend backend)          → restore terminal, cleanup
+  (suspend-backend backend)           → temporary suspend (SIGTSTP)
+  (resume-backend backend)            → re-initialize after resume
+
+  ;; ── Output ──
+  (backend-size backend)              → (values columns lines)
+  (backend-write backend string)      → raw output to terminal
+  (begin-sync backend)                → start synchronized update
+  (end-sync backend)                  → flush synchronized update
+  (backend-clear backend)             → clear entire screen
+
+  ;; ── Drawing primitives ──
+  (draw-rect backend x y w h ch style)           → fill rectangle
+  (draw-text backend x y str fg bg attrs)        → render text at position
+  (draw-border backend x y w h style attrs)      → draw border rectangle
+  (draw-ellipsis backend x y w)                  → truncated text marker
+  (draw-link backend x y str url fg bg attrs)    → OSC 8 hyperlink
+
+  ;; ── Cursor ──
+  (cursor-move backend x y)            → position cursor
+  (cursor-hide backend)                → hide cursor
+  (cursor-show backend)                → show cursor
+  (cursor-style backend :bar|:block|:underline &optional blink)
+
+  ;; ── Input ──
+  (read-event backend)                 → (values event-type event-data)
+  (enable-mouse backend)               → enable SGR mouse reporting
+  (enable-bracketed-paste backend)     → enable paste detection
+  (set-keyboard-mode backend :kitty|:default)
+
+  ;; ── Capability queries ──
+  (capable-p backend :truecolor|:osc8|:kitty-keyboard|:sync|:sixel|:mouse)
+#+END_SRC
+
+*** Style structure
+
+All drawing functions accept a =style= plist that is resolved through
+the theme engine before reaching the backend:
+
+#+BEGIN_SRC
+  (:fg :error                     ; semantic role from theme
+   :bg :background-panel          ; resolved to hex by theme
+   :bold t
+   :italic nil
+   :underline nil
+   :blink nil
+   :reverse nil
+   :dim nil
+   :hyperlink-url nil)            ; OSC 8 URL if set
+#+END_SRC
+
+The backend receives resolved hex colors, not semantic roles. Theme
+resolution happens in the pipeline layer, before backend dispatch.
+
+*** Backend Selection
+
+At startup:
+
+#+BEGIN_SRC
+  1. Check if stdout is a TTY (if not → simple-backend)
+  2. Send DA1 query: ESC [ c
+     - No response within 100ms → simple-backend
+     - Response parsed → check for modern features
+  3. Try DA3 (secondary device attributes):
+     - Kitty reports "Kitty" + protocol version
+     - WezTerm reports "WezTerm"
+     - iTerm2 reports specific codes
+  4. Query DECRPM for DECICM sync:
+     - ESC [?2026$p
+     - Response ESC [?2026;1$y = supported
+  5. If sync + truecolor + kitty keyboard → modern-backend
+     Otherwise → simple-backend
+#+END_SRC
+
+** Layout Engine
+
+The layout engine is pure Common Lisp — no Yoga FFI, no C dependencies.
+
+*** Constraint Model
+
+A terminal has ~200x80 cells. The constraint solver only needs to
+handle one-dimensional layout in two passes:
+
+1. **Column direction (vertical pass):** distribute Y positions, sum
+   children heights. Width is inherited from parent (minus padding).
+2. **Row direction (horizontal pass):** distribute X positions, sum
+   children widths. Height is inherited from parent.
+
+Flex properties:
+- =:grow= — proportional distribution of remaining space
+- =:shrink= — proportional reduction when content overflows
+- =:basis= — initial size before grow/shrink
+- =:wrap= — overflow moves to next row/column
+- =:gap= — spacing between children
+
+Position properties:
+- =:relative= — normal flow (default)
+- =:absolute= — positioned relative to parent's content box
+- =:top=, =:right=, =:bottom=, =:left= — offset for absolute
+
+This is a subset of CSS Flexbox. Enough for every TUI layout pattern
+(sidebar + content, toolbar + main + status, dialog overlay, tab
+navigation, split panes). ~200 lines.
+
+*** Layout Node
+
+#+BEGIN_SRC
+  (defclass layout-node ()
+    ;; Computed by solver
+    (x y width height             ; computed position + size
+     children                     ; list of child layout-nodes
+     parent                       ; parent layout-node (or nil for root)
+     ;; Style input
+     direction                    ; :row | :column | :row-reverse | :column-reverse
+     wrap                         ; :nowrap | :wrap | :wrap-reverse
+     grow shrink basis            ; flex sizing
+     align-self align-items       ; cross-axis alignment
+     justify-content              ; main-axis distribution
+     padding margin border        ; box model
+     gap                          ; spacing between children
+     position-type                ; :relative | :absolute
+     position-offset))            ; top/left for absolute
+#+END_SRC
+
+*** Composable API
+
+#+BEGIN_SRC
+  (vbox (:gap 1 :padding 1)
+    (header "Title")
+    (hbox (:grow 1)
+      (sidebar (:width 30) ...)
+      (content ...)))
+#+END_SRC
+
+Macros expand to layout-node construction + child wiring.
+
+** Component Tree
+
+Components are CLOS objects. Every component has a =layout-node=
+slot that drives positioning. Components define =render= methods.
+
+*** Base Component Class
+
+#+BEGIN_SRC
+  (defclass component ()
+    (layout-node         ; layout-node for this component
+     parent              ; parent component (or nil for root)
+     children            ; list of child components
+     dirty               ; t/nil — needs re-render
+     theme               ; theme reference
+     visible))           ; t/nil
+#+END_SRC
+
+*** Generic Functions
+
+- =(render component backend)= — returns list of render commands
+- =(handle-key component event)= — returns t if consumed
+- =(handle-mouse component event)= — returns t if consumed
+- =(measure component max-width max-height)= — returns (values w h)
+- =(children component)= — returns list of child components
+- =(find-focused component)= — returns the focused child (or nil)
+
+*** Rendering Pipeline
+
+#+BEGIN_SRC
+  1. (propagate-dirty root)     → mark ancestors dirty
+  2. (compute-layout root w h)  → pure CL constraint solve
+  3. (collect-commands root)     → walk dirty branches, call render
+  4. (diff-framebuffer prev curr) → emit only changed cells
+  5. (begin-sync backend)       → DECICM start
+  6. (flush-commands backend)   → write escape sequences
+  7. (end-sync backend)         → DECICM end
+  8. (clear-dirty root)         → mark all clean
+#+END_SRC
+
+** Input Handling
+
+Input goes through a layered keybinding system:
+
+1. Terminal emits escape sequences → parser converts to events
+2. Events dispatched through layers: =:global= → =:local= → =:focused=
+3. Focused component's =handle-key= fires first
+4. Unconsumed events bubble to =:local= keymap, then =:global=
+5. Modal layers (dialog) intercept before global
+
+Mouse events follow the same path, with hit-testing routing to the
+deepest component containing the click coordinates.
+
+** Theme Engine
+
+Semantic tokens → hex colors → backend color pairs. No code references
+hex values directly. =:accent= resolves to gold in default theme, blue
+in nord, green in gruvbox, depending on which preset is active.
+
+Presets define both =:dark= and =:light= variants. Auto-detection
+reads terminal background color at startup.
+
+** File Structure
+
+#+BEGIN_SRC
+  cl-tui/
+  ├── cl-tui.asd
+  ├── cl-tui-tests.asd
+  ├── README.org
+  ├── LICENSE
+  ├── docs/
+  │   ├── ROADMAP.org
+  │   └── ARCHITECTURE.org          ← this file
+  ├── src/
+  │   ├── package.lisp
+  │   ├── backend/
+  │   │   ├── protocol.lisp
+  │   │   ├── detection.lisp
+  │   │   ├── simple.lisp
+  │   │   └── modern.lisp
+  │   ├── layout/
+  │   │   ├── nodes.lisp
+  │   │   ├── solver.lisp
+  │   │   └── api.lisp
+  │   ├── components/
+  │   │   ├── base.lisp
+  │   │   ├── box.lisp
+  │   │   └── text.lisp
+  │   ├── rendering/
+  │   │   ├── pipeline.lisp
+  │   │   ├── dirty.lisp
+  │   │   └── diff.lisp
+  │   └── theme/
+  │       ├── tokens.lisp
+  │       └── presets.lisp
+  └── tests/
+      ├── package.lisp
+      ├── backend.lisp
+      ├── layout.lisp
+      └── components.lisp
+#+END_SRC
+
+** Dependency Graph
+
+  backend/     (no deps)
+  layout/      (no deps — pure math)
+  theme/       (backend for color resolution)
+  components/  (layout, theme, rendering)
+  rendering/   (layout, components, backend, theme)
+  input/       (backend for raw events)
+
+Init order:
+  1. Backend — detect, initialize
+  2. Theme — load default preset
+  3. Layout — construct component tree
+  4. Render — layout → commands → flush
+  5. Input — event loop (blocks on read-event)

docs/ROADMAP.org

@@ -5,10 +5,81 @@
 * The Roadmap
 
 Each phase is one minor release. Phases ship in dependency order — each depends on
-the components from prior phases. The layout engine ships first because everything
+the components from prior phases. The backend protocol ships first because
-else builds on it.
+everything else builds on it.
 
-Feature releases increment the minor version (v0.X.0). Bugfix releases increment
+** v0.0.1: Foundation — Backend Protocol
+
+The abstraction layer that makes everything portable. Two backends:
+=modern= (raw escape sequences, truecolor, modern features) and =simple=
+(ASCII art, universal compatibility). The component tree never touches
+the terminal directly — it dispatches through the protocol.
+
+*** TODO Backend protocol definition
+:PROPERTIES:
+:ID:       id-v000-protocol
+:CREATED:  [2026-05-10 Sat]
+:END:
+
+- Define =backend= abstract class with generic functions:
+  - =initialize-backend=, =shutdown-backend=, =suspend-backend=, =resume-backend=
+  - =backend-size=, =backend-write=, =backend-clear=
+  - =begin-sync=, =end-sync= — DECICM synchronized updates
+  - =draw-rect=, =draw-text=, =draw-border=, =draw-ellipsis=, =draw-link=
+  - =cursor-move=, =cursor-hide=, =cursor-show=, =cursor-style=
+  - =read-event=, =enable-mouse=, =enable-bracketed-paste=, =set-keyboard-mode=
+  - =capable-p= — query feature support
+- Style plist structure: ~(:fg :error :bg :background-panel :bold t :italic nil ...)~
+- ~100 lines
+
+*** TODO Simple backend
+:PROPERTIES:
+:ID:       id-v000-simple
+:CREATED:  [2026-05-10 Sat]
+:END:
+
+- =simple-backend= class — inherits =backend=
+- Borders: ASCII (~+-|~), no rounded corners
+- No color, no bold/italic — plain characters only
+- No OSC 8 links, no mouse, no synchronized updates
+- Works on any terminal, any SSH connection, piped output
+- ~100 lines
+
+*** TODO Modern backend
+:PROPERTIES:
+:ID:       id-v000-modern
+:CREATED:  [2026-05-10 Sat]
+:END:
+
+- =modern-backend= class — inherits =backend=
+- Truecolor 24-bit foreground/background
+- Rounded, single, double border styles via Unicode box-drawing
+- OSC 8 hyperlinks (clickable URLs)
+- DECICM synchronized updates (flicker-free)
+- SGR mouse tracking + kitty keyboard protocol
+- Bracketed paste detection
+- Bold, italic, underline, dim, blink, reverse, strikethrough
+- Cursor style: =:bar=, =:block=, =:underline=, with blink option
+- ~250 lines
+
+*** TODO Terminal capability detection
+:PROPERTIES:
+:ID:       id-v000-detection
+:CREATED:  [2026-05-10 Sat]
+:END:
+
+- =detect-backend= → returns =modern-backend= or =simple-backend=
+- Check if stdout is a TTY (if not → =simple-backend=)
+- Send DA1 (~ESC[c~) query, 100ms timeout
+- Send DA3 (~ESC[?c~) for kitty/wezterm identification
+- Query DECRPM (~ESC[?2026$p~) for DECICM sync support
+- Query truecolor support via =COLORTERM= env var + DA response
+- Cache detection result so subsequent calls are instant
+- ~100 lines
+
+~550 lines total. Dependencies: None (pure CL, no FFI, no external libs).
+
+** v0.0.2: Layout Engine
 the patch version (v0.X.Y).
 
 ** File Update Checklist

layout/layout.lisp

@@ -0,0 +1,188 @@
+;;; layout — Pure CL Flexbox layout engine
+
+(defpackage :cl-tui.layout
+  (:use :cl)
+  (:export
+   #:layout-node #:make-layout-node
+   #:layout-node-add-child #:layout-node-remove-child
+   #:layout-node-children
+   #:layout-node-x #:layout-node-y
+   #:layout-node-width #:layout-node-height
+   #:layout-node-direction
+   #:compute-layout
+   #:vbox #:hbox #:spacer
+   ;; For tests
+   #:layout-node-parent #:layout-node-fixed-width
+   #:layout-node-fixed-height #:normalize-box
+   #:box-edge))
+
+(in-package :cl-tui.layout)
+
+(defun normalize-box (spec)
+  (cond ((null spec) '(:top 0 :right 0 :bottom 0 :left 0))
+        ((numberp spec) `(:top ,spec :right ,spec :bottom ,spec :left ,spec))
+        ((getf spec :top) spec)
+        (t '(:top 0 :right 0 :bottom 0 :left 0))))
+
+(defun box-edge (box edge)
+  (or (getf box edge) 0))
+
+(defclass layout-node ()
+  ((parent   :initform nil :accessor layout-node-parent)
+   (children :initform nil :accessor layout-node-children)
+   (x :initform 0 :accessor layout-node-x)
+   (y :initform 0 :accessor layout-node-y)
+   (width :initform 0 :accessor layout-node-width)
+   (height :initform 0 :accessor layout-node-height)
+   (direction :initform :column :initarg :direction :accessor layout-node-direction)
+   (grow :initform 0 :initarg :grow :accessor layout-node-grow)
+   (shrink :initform 1 :initarg :shrink :accessor layout-node-shrink)
+   (padding :initform '(:top 0 :right 0 :bottom 0 :left 0) :initarg :padding :accessor layout-node-padding)
+   (margin :initform '(:top 0 :right 0 :bottom 0 :left 0) :initarg :margin :accessor layout-node-margin)
+   (gap :initform 0 :initarg :gap :accessor layout-node-gap)
+   (position-type :initform :relative :initarg :position-type :accessor layout-node-position-type)
+   (position-offset :initform nil :initarg :position-offset :accessor layout-node-position-offset)
+   (fixed-width :initform nil :initarg :width :accessor layout-node-fixed-width)
+   (fixed-height :initform nil :initarg :height :accessor layout-node-fixed-height)))
+
+(defun make-layout-node (&key direction grow shrink padding margin gap
+                         position-type position-offset width height)
+  (make-instance 'layout-node
+    :direction (or direction :column)
+    :grow (or grow 0) :shrink (or shrink 1)
+    :padding (normalize-box padding) :margin (normalize-box margin)
+    :gap (or gap 0)
+    :position-type (or position-type :relative)
+    :position-offset position-offset
+    :width width :height height))
+
+(defun layout-node-add-child (parent child)
+  (setf (layout-node-parent child) parent)
+  (setf (layout-node-children parent)
+        (nconc (layout-node-children parent) (list child)))
+  child)
+
+(defun layout-node-remove-child (parent child)
+  (setf (layout-node-parent child) nil)
+  (setf (layout-node-children parent)
+        (delete child (layout-node-children parent)))
+  child)
+
+;; ── Solver ─────────────────────────────────────────────────────
+
+(defun distribute-sizes (children avail gap horizontal)
+  "Compute child sizes given available space and gap.
+HORIZONTAL is non-nil when distributing width (row layout).
+Each child starts from its fixed size (if any). Remaining space
+is distributed by grow ratio; overflow is reduced by shrink ratio."
+  (let* ((n (length children))
+         (gap-total (* gap (max 0 (1- n))))
+         (base (mapcar (lambda (c)
+                         (or (if horizontal
+                                 (layout-node-fixed-width c)
+                                 (layout-node-fixed-height c))
+                             0))
+                       children))
+         (base-total (reduce #'+ base))
+         (remaining (- avail base-total gap-total))
+         (grow-total (reduce #'+ (mapcar #'layout-node-grow children)))
+         (shrink-total (reduce #'+ (mapcar #'layout-node-shrink children))))
+    (mapcar (lambda (c b)
+              (let ((sz b))
+                (when (and (plusp remaining) (plusp grow-total))
+                  (incf sz (round (* remaining (/ (layout-node-grow c) grow-total)))))
+                (when (and (minusp remaining) (plusp shrink-total))
+                  (decf sz (round (* (abs remaining) (/ (layout-node-shrink c) shrink-total)))))
+                (max 1 sz)))
+            children base)))
+
+(defun compute-layout (root available-width available-height)
+  "Layout all children of ROOT within the given dimensions.
+Recursively computes position and size for every node."
+  (labels ((place-children (node x y max-w max-h)
+             (let* ((children (layout-node-children node))
+                    (is-row (eql (layout-node-direction node) :row))
+                    (pl (box-edge (layout-node-padding node) :left))
+                    (pt (box-edge (layout-node-padding node) :top))
+                    (pr (box-edge (layout-node-padding node) :right))
+                    (pb (box-edge (layout-node-padding node) :bottom))
+                    (cw (max 0 (- max-w pl pr)))
+                    (ch (max 0 (- max-h pt pb)))
+                    (gap (layout-node-gap node))
+                    (sizes (distribute-sizes children (if is-row cw ch) gap is-row)))
+               ;; Position the node (content area starts at padding inset)
+               (setf (layout-node-x node) (+ x pl)
+                     (layout-node-y node) (+ y pt))
+               ;; Place each child sequentially
+               (loop :with pos = 0
+                     :for child :in children
+                     :for size :in sizes
+                     :do (if is-row
+                             (setf (layout-node-width child) size
+                                   (layout-node-x child) (+ x pl pos)
+                                   (layout-node-height child) ch
+                                   (layout-node-y child) (+ y pt))
+                             (setf (layout-node-height child) size
+                                   (layout-node-y child) (+ y pt pos)
+                                   (layout-node-width child) cw
+                                   (layout-node-x child) (+ x pl)))
+                         (place-children child
+                                         (layout-node-x child)
+                                         (layout-node-y child)
+                                         (if is-row size cw)
+                                         (if is-row ch size))
+                         (incf pos (+ size gap)))
+               ;; Compute own size from children
+               (let ((last-child (car (last children))))
+                 (if is-row
+                     (setf (layout-node-width node)
+                           (or (layout-node-fixed-width node)
+                               (if last-child
+                                   (+ (layout-node-x node)
+                                      (layout-node-width last-child)
+                                      pr)
+                                   max-w))
+                           (layout-node-height node)
+                           max-h)
+                     (setf (layout-node-height node)
+                           (or (layout-node-fixed-height node)
+                               (if last-child
+                                   (let ((last-y (layout-node-y last-child))
+                                         (last-h (layout-node-height last-child)))
+                                     (+ last-y last-h pb))
+                                   max-h))
+                           (layout-node-width node)
+                           max-w))))))
+    (place-children root 0 0 available-width available-height)
+    root))
+
+;; ── Macros ─────────────────────────────────────────────────────
+
+(defmacro vbox ((&key grow shrink padding margin gap width height) &body children)
+  (let ((n (gensym)))
+    `(let ((,n (make-layout-node :direction :column
+                ,@(when grow `(:grow ,grow))
+                ,@(when shrink `(:shrink ,shrink))
+                ,@(when padding `(:padding ,padding))
+                ,@(when margin `(:margin ,margin))
+                ,@(when gap `(:gap ,gap))
+                ,@(when width `(:width ,width))
+                ,@(when height `(:height ,height)))))
+       ,@(loop for c in children collect `(layout-node-add-child ,n ,c))
+       ,n)))
+
+(defmacro hbox ((&key grow shrink padding margin gap width height) &body children)
+  (let ((n (gensym)))
+    `(let ((,n (make-layout-node :direction :row
+                ,@(when grow `(:grow ,grow))
+                ,@(when shrink `(:shrink ,shrink))
+                ,@(when padding `(:padding ,padding))
+                ,@(when margin `(:margin ,margin))
+                ,@(when gap `(:gap ,gap))
+                ,@(when width `(:width ,width))
+                ,@(when height `(:height ,height)))))
+       ,@(loop for c in children collect `(layout-node-add-child ,n ,c))
+       ,n)))
+
+(defmacro spacer (&key grow)
+  `(make-layout-node :grow ,(or grow 1)))

layout/tests.lisp

@@ -0,0 +1,175 @@
+(defpackage :cl-tui-layout-test
+  (:use :cl :fiveam :cl-tui.layout)
+  (:export #:run-tests))
+(in-package :cl-tui-layout-test)
+
+(def-suite layout-suite :description "Layout engine tests")
+(in-suite layout-suite)
+
+(defun run-tests ()
+  (let ((result (run 'layout-suite)))
+    (fiveam:explain! result)
+    (uiop:quit 0)))
+
+(test make-layout-node-defaults
+  (let ((n (make-layout-node)))
+    (is (typep n 'layout-node))
+    (is (eql (layout-node-direction n) :column))))
+
+(test make-layout-node-row
+  (let ((n (make-layout-node :direction :row)))
+    (is (eql (layout-node-direction n) :row))))
+
+(test add-child-sets-parent
+  (let ((parent (make-layout-node)) (child (make-layout-node)))
+    (layout-node-add-child parent child)
+    (is (eql (layout-node-parent child) parent))
+    (is (= (length (layout-node-children parent)) 1))))
+
+(test remove-child-clears-parent
+  (let ((parent (make-layout-node)) (child (make-layout-node)))
+    (layout-node-add-child parent child)
+    (layout-node-remove-child parent child)
+    (is (null (layout-node-parent child)))
+    (is (= (length (layout-node-children parent)) 0))))
+
+(test column-two-children-vertical
+  (let* ((root (make-layout-node :direction :column))
+         (c1 (make-layout-node :height 3))
+         (c2 (make-layout-node :height 5)))
+    (layout-node-add-child root c1) (layout-node-add-child root c2)
+    (compute-layout root 20 20)
+    (is (= (layout-node-y c1) 0)) (is (= (layout-node-height c1) 3))
+    (is (= (layout-node-y c2) 3)) (is (= (layout-node-height c2) 5))))
+
+(test row-two-children-horizontal
+  (let* ((root (make-layout-node :direction :row))
+         (c1 (make-layout-node :width 10))
+         (c2 (make-layout-node :width 5)))
+    (layout-node-add-child root c1) (layout-node-add-child root c2)
+    (compute-layout root 20 10)
+    (is (= (layout-node-x c1) 0)) (is (= (layout-node-width c1) 10))
+    (is (= (layout-node-x c2) 10)) (is (= (layout-node-width c2) 5))))
+
+(test flex-grow-distributes-space
+  (let* ((root (make-layout-node :direction :row :width 20))
+         (c1 (make-layout-node :width 4 :grow 1))
+         (c2 (make-layout-node :width 4 :grow 2)))
+    (layout-node-add-child root c1) (layout-node-add-child root c2)
+    (compute-layout root 20 10)
+    (is (= (layout-node-width c1) 8)) (is (= (layout-node-width c2) 12))))
+
+(test flex-grow-single-child
+  (let* ((root (make-layout-node :direction :row :width 20))
+         (c (make-layout-node :width 5 :grow 1)))
+    (layout-node-add-child root c)
+    (compute-layout root 20 10)
+    (is (= (layout-node-width c) 20))))
+
+(test flex-shrink-reduces-overflow
+  (let* ((root (make-layout-node :direction :row :width 10))
+         (c1 (make-layout-node :width 8 :shrink 1))
+         (c2 (make-layout-node :width 8 :shrink 1)))
+    (layout-node-add-child root c1) (layout-node-add-child root c2)
+    (compute-layout root 10 10)
+    (is (= (layout-node-width c1) 5)) (is (= (layout-node-width c2) 5))))
+
+(test padding-reduces-content-area
+  (let* ((root (make-layout-node :direction :column :padding '(:top 1 :left 1 :bottom 1 :right 1)))
+         (c (make-layout-node :height 3)))
+    (layout-node-add-child root c)
+    (compute-layout root 20 10)
+    (is (= (layout-node-x c) 1)) (is (= (layout-node-y c) 1))
+    (is (= (layout-node-height c) 3))))
+
+(test gap-between-children
+  (let* ((root (make-layout-node :direction :column :gap 2))
+         (c1 (make-layout-node :height 3))
+         (c2 (make-layout-node :height 3)))
+    (layout-node-add-child root c1) (layout-node-add-child root c2)
+    (compute-layout root 20 20)
+    (is (= (layout-node-y c1) 0)) (is (= (layout-node-y c2) 5))))
+
+(test vbox-macro
+  (let ((r (vbox () (make-layout-node :height 3) (make-layout-node :height 5))))
+    (compute-layout r 20 20)
+    (is (= (length (layout-node-children r)) 2))
+    (is (= (layout-node-y (elt (layout-node-children r) 1)) 3))))
+
+(test hbox-macro
+  (let ((r (hbox () (make-layout-node :width 5) (make-layout-node :width 3))))
+    (compute-layout r 20 10)
+    (is (= (length (layout-node-children r)) 2))
+    (is (= (layout-node-x (elt (layout-node-children r) 1)) 5))))
+
+(test spacer-takes-grow
+  (let ((r (hbox (:width 20) (make-layout-node :width 5) (spacer :grow 1) (make-layout-node :width 5))))
+    (compute-layout r 20 10)
+    (let ((c (layout-node-children r)))
+      (is (= (layout-node-x (elt c 2)) 15)) (is (= (layout-node-width (elt c 1)) 10)))))
+
+(test nested-vbox-in-hbox
+  (let* ((sidebar (vbox (:width 5 :height 10) (make-layout-node :height 3) (make-layout-node :height 7)))
+         (main (vbox (:grow 1 :height 10) (make-layout-node :height 2) (make-layout-node :grow 1)))
+         (r (hbox (:width 30 :height 10) sidebar main)))
+    (compute-layout r 30 10)
+    (is (= (layout-node-width sidebar) 5))
+    (is (>= (layout-node-width main) 20))
+    (let ((sc (layout-node-children sidebar)))
+      (is (= (layout-node-y (elt sc 0)) 0))
+      (is (= (layout-node-y (elt sc 1)) 3)))))
+
+;; ── Edge Cases ────────────────────────────────────────────────
+
+(test empty-container-does-not-crash
+  "compute-layout on a node with no children should not error"
+  (let ((r (make-layout-node)))
+    (compute-layout r 20 20)
+    (is (integerp (layout-node-width r)))
+    (is (integerp (layout-node-height r)))))
+
+(test single-child-in-column
+  "A column with one child places it correctly"
+  (let* ((r (make-layout-node :direction :column :width 10 :height 20))
+         (c (make-layout-node :height 5)))
+    (layout-node-add-child r c)
+    (compute-layout r 10 20)
+    (is (= (layout-node-y c) 0))
+    (is (= (layout-node-height c) 5))))
+
+(test zero-size-container
+  "compute-layout with zero available space should not error"
+  (let* ((r (make-layout-node :direction :column))
+         (c (make-layout-node :height 5)))
+    (layout-node-add-child r c)
+    (compute-layout r 0 0)
+    (is (integerp (layout-node-x c)))
+    (is (integerp (layout-node-y c)))))
+
+(test deep-nesting-three-levels
+  "Three-level deep nesting produces correct leaf positions"
+  (let* ((out (vbox ()                                    ; outer box
+                (vbox (:grow 1)                           ; middle box
+                  (make-layout-node :height 2))))         ; leaf
+         (leaf (elt (layout-node-children
+                      (elt (layout-node-children out) 0)) 0)))
+    (compute-layout out 20 20)
+    (is (= (layout-node-y leaf) 0))))
+
+(test large-padding-leaves-room
+  "Large padding reduces content area but doesn't crash"
+  (let* ((r (make-layout-node :direction :column
+                              :padding '(:top 5 :left 5 :bottom 5 :right 5)))
+         (c (make-layout-node :height 3)))
+    (layout-node-add-child r c)
+    (compute-layout r 20 20)
+    (is (= (layout-node-x c) 5))
+    (is (= (layout-node-y c) 5))))
+
+(test negative-grow-is-clamped
+  "Grow values are adjusted but still compute"
+  (let* ((r (make-layout-node :direction :row :width 10))
+         (c (make-layout-node :width 5 :grow -1)))
+    (layout-node-add-child r c)
+    (compute-layout r 10 10)
+    (is (integerp (layout-node-width c)))))

org/backend-protocol.org

@@ -0,0 +1,382 @@
+#+TITLE: cl-tui Backend Protocol — v0.0.1
+#+STARTUP: content
+#+FILETAGS: :cl-tui:backend:v0.0.1:
+#+OPTIONS: ^:nil
+
+* Backend Protocol
+
+The backend protocol is the rendering abstraction layer. Every visual
+operation dispatches through generic functions on a backend class.
+Two implementations exist: =modern-backend= (raw escape sequences,
+truecolor, modern terminal features) and =simple-backend= (ASCII art,
+universal compatibility).
+
+** Contract
+
+*** Backend Lifecycle
+
+- =(initialize-backend backend)= → backend
+  Initialize the terminal, set raw mode, enable features.
+  Returns the backend instance.
+
+- =(shutdown-backend backend)= → nil
+  Restore terminal to cooked mode, reset colors, show cursor.
+  Must be called on exit regardless of how the image stops.
+
+- =(backend-size backend)= → (values columns lines integer integer)
+  Return terminal dimensions. First value = columns, second = lines.
+
+- =(backend-write backend string)= → integer
+  Write raw string to terminal output. Returns number of bytes written.
+
+- =(backend-clear backend)= → nil
+  Clear the entire screen and reset cursor to (0,0).
+
+*** Rendering Primitives
+
+- =(draw-text backend x y string fg bg &key bold italic underline reverse dim blink)= → nil
+  Render text at position (x, y). fg and bg are hex color strings
+  (e.g. "#FFD700") or nil for default. Attributes are booleans.
+
+- =(draw-border backend x y width height &key style fg bg title title-align)= → nil
+  Draw a border rectangle. Style is :single, :double, or :rounded.
+
+- =(draw-rect backend x y width height &key bg)= → nil
+  Fill a rectangle with background color.
+
+- =(draw-link backend x y string url &key fg bg)= → nil
+  Render clickable hyperlink (OSC 8 escape sequence).
+
+- =(draw-ellipsis backend x y width &key fg bg)= → nil
+  Render "..." truncated text marker at position.
+
+*** Cursor Operations
+
+- =(cursor-move backend x y)= → nil
+  Move cursor to position (x, y). Origin is top-left (0,0).
+
+- =(cursor-hide backend)= → nil
+- =(cursor-show backend)= → nil
+
+- =(cursor-style backend shape &key blink)= → nil
+  shape is :block, :bar, or :underline.
+
+*** Synchronization
+
+- =(begin-sync backend)= → nil
+  Start synchronized update (DECICM). All subsequent output is buffered
+  by the terminal until =end-sync=.
+
+- =(end-sync backend)= → nil
+  Flush synchronized update buffer. The entire frame appears at once.
+
+*** Input
+
+- =(read-event backend &key timeout)= → (values keyword list)
+  Read next input event. Blocks until event or timeout.
+  Returns event type keyword and event data plist.
+
+- =(enable-mouse backend)= → nil
+  Enable SGR mouse tracking (press, release, drag, scroll).
+
+- =(enable-bracketed-paste backend)= → nil
+  Enable bracketed paste mode.
+
+*** Capability Queries
+
+- =(capable-p backend feature)= → boolean
+  Feature is :truecolor, :osc8, :sync, :mouse, :bracketed-paste,
+  :kitty-keyboard, :sixel, :cursor-style.
+
+** Backend Classes
+
+*** Simple Backend
+
+=(make-simple-backend)= → simple-backend
+
+The minimal backend. ASCII borders, no color, no modern features.
+Works everywhere — SSH, serial, pipes, ancient terminals.
+
+Borders:
+- Single: + - |
+- Double: + = |
+- Rounded: + - |  (same as single — no rounded chars)
+
+No color, no bold, no italic, no links, no mouse, no sync.
+
+*** Modern Backend
+
+=(make-modern-backend)= → modern-backend
+
+Full-featured backend. Truecolor, Unicode box-drawing, OSC 8 links,
+DECICM sync, mouse tracking, kitty keyboard protocol.
+
+Borders:
+- Single: ┌ ─ ┐ │ └ ┘
+- Double: ╔ ═ ╗ ║ ╚ ╝
+- Rounded: ╭ ─ ╮ │ ╰ ╯
+
+** Test Suite
+
+#+BEGIN_SRC lisp
+(defpackage :cl-tui-backend-test
+  (:use :cl :fiveam)
+  (:export #:run!))
+(in-package :cl-tui-backend-test)
+
+(def-suite backend-suite :description "Backend protocol tests")
+(in-suite backend-suite)
+
+;; ── Simple Backend ──────────────────────────────────────────────
+
+(test simple-backend-lifecycle
+  "simple-backend can be created and shut down"
+  (let ((b (make-simple-backend)))
+    (is (typep b 'simple-backend))
+    (initialize-backend b)
+    (is (capable-p b :truecolor) nil "simple backend has no truecolor")
+    (shutdown-backend b)))
+
+(test simple-backend-draw-text
+  "simple-backend renders text at position, ignoring style"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (draw-text b 0 0 "hello" nil nil)
+    ;; No crash = pass (simple backend writes to *standard-output*)
+    (shutdown-backend b)
+    (is-t t)))
+
+(test simple-backend-border-single
+  "simple-backend draws ASCII single border"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (draw-border b 0 0 10 5 :style :single)
+    (shutdown-backend b)
+    (is-t t)))
+
+(test simple-backend-border-rounded
+  "simple-backend falls back to straight edges for rounded"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (draw-border b 0 0 10 5 :style :rounded)
+    ;; No error — rounded falls back to single on simple
+    (shutdown-backend b)
+    (is-t t)))
+
+;; ── Backend Capabilities ───────────────────────────────────────
+
+(test capable-p-known-features
+  "capable-p returns nil for all features on simple-backend"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (dolist (f '(:truecolor :osc8 :sync :mouse :bracketed-paste
+                 :kitty-keyboard :sixel :cursor-style))
+      (is (capable-p b f) nil
+          (format nil "~s should not be supported on simple-backend" f)))
+    (shutdown-backend b)))
+
+;; ── Backend Size ───────────────────────────────────────────────
+
+(test backend-size-returns-integers
+  "backend-size returns two integer values"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (multiple-value-bind (cols lines) (backend-size b)
+      (is (integerp cols))
+      (is (integerp lines))
+      (is (>= cols 10))
+      (is (>= lines 3)))
+    (shutdown-backend b)))
+
+;; ── Drawing Primitives ─────────────────────────────────────────
+
+(test draw-rect-fills-area
+  "draw-rect fills a rectangular area with background"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (draw-rect b 0 0 5 3 :bg nil)
+    (shutdown-backend b)
+    (is-t t)))
+
+(test draw-text-multi-line
+  "draw-text handles strings with newlines"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (draw-text b 0 0 "line1~%line2" nil nil)
+    (shutdown-backend b)
+    (is-t t)))
+
+;; ── Synchronization ────────────────────────────────────────────
+
+(test sync-is-noop-on-simple
+  "begin-sync and end-sync are no-ops on simple-backend"
+  (let ((b (make-simple-backend)))
+    (initialize-backend b)
+    (begin-sync b)
+    (draw-text b 0 0 "in sync" nil nil)
+    (end-sync b)
+    (shutdown-backend b)
+    (is-t t)))
+#+END_SRC
+
+** Implementation
+
+*** Package
+
+#+BEGIN_SRC lisp
+(defpackage :cl-tui.backend
+  (:use :cl)
+  (:export
+   ;; Backend classes
+   #:backend #:simple-backend
+   ;; Lifecycle
+   #:initialize-backend #:shutdown-backend
+   #:backend-size #:backend-write #:backend-clear
+   ;; Drawing
+   #:draw-text #:draw-border #:draw-rect
+   #:draw-link #:draw-ellipsis
+   ;; Cursor
+   #:cursor-move #:cursor-hide #:cursor-show #:cursor-style
+   ;; Sync
+   #:begin-sync #:end-sync
+   ;; Input
+   #:read-event #:enable-mouse #:enable-bracketed-paste
+   ;; Queries
+   #:capable-p
+   ;; Constructors
+   #:make-simple-backend))
+(in-package :cl-tui.backend)
+#+END_SRC
+
+*** Backend Base Class
+
+#+BEGIN_SRC lisp
+(defclass backend () ())
+
+(defgeneric initialize-backend (backend)
+  (:method ((b backend)) b))
+
+(defgeneric shutdown-backend (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric backend-size (backend)
+  (:method ((b backend))
+    (values 80 24)))
+
+(defgeneric backend-write (backend string))
+
+(defgeneric backend-clear (backend)
+  (:method ((b backend))
+    (backend-write b (string #\escape) "[2J")
+    (cursor-move b 0 0)))
+
+(defgeneric draw-text (backend x y string fg bg &key
+                       bold italic underline reverse dim blink))
+
+(defgeneric draw-border (backend x y width height
+                         &key style fg bg title title-align))
+
+(defgeneric draw-rect (backend x y width height &key bg))
+
+(defgeneric draw-link (backend x y string url &key fg bg))
+
+(defgeneric draw-ellipsis (backend x y width &key fg bg))
+
+(defgeneric cursor-move (backend x y))
+
+(defgeneric cursor-hide (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric cursor-show (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric cursor-style (backend shape &key blink)
+  (:method ((b backend) shape &key blink) (values)))
+
+(defgeneric begin-sync (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric end-sync (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric read-event (backend &key timeout)
+  (:method ((b backend) &key timeout) (values nil nil)))
+
+(defgeneric enable-mouse (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric enable-bracketed-paste (backend)
+  (:method ((b backend)) (values)))
+
+(defgeneric capable-p (backend feature)
+  (:method ((b backend) feature)
+    (declare (ignore feature))
+    nil))
+#+END_SRC
+
+*** Simple Backend
+
+#+BEGIN_SRC lisp
+(defclass simple-backend (backend)
+  ((output-stream :initform *standard-output*
+                  :accessor backend-output-stream)))
+
+(defmethod initialize-backend ((b simple-backend))
+  b)
+
+(defmethod shutdown-backend ((b simple-backend))
+  (values))
+
+(defmethod backend-size ((b simple-backend))
+  ;; Try ioctl, fall back to 80x24
+  (values 80 24))
+
+(defmethod backend-write ((b simple-backend) string)
+  (let ((stream (backend-output-stream b)))
+    (write-string string stream)
+    (finish-output stream)
+    (length string)))
+
+(defmethod draw-text ((b simple-backend) x y string fg bg
+                      &key bold italic underline reverse dim blink)
+  (declare (ignore x y fg bg bold italic underline reverse dim blink))
+  (backend-write b string))
+
+(defun %simple-border-char (edge-style pos)
+  "Return ASCII border character for EDGE-STYLE at POS.
+POS is :top-left, :top-right, :bottom-left, :bottom-right,
+:horizontal, or :vertical."
+  (case pos
+    ((:top-left :top-right :bottom-left :bottom-right) #\+)
+    (:horizontal #\-)
+    (:vertical #\|)))
+
+(defmethod draw-border ((b simple-backend) x y width height
+                        &key style fg bg title title-align)
+  (declare (ignore style fg bg title title-align))
+  (let ((h (%simple-border-char nil :horizontal))
+        (v (%simple-border-char nil :vertical)))
+    ;; Top edge
+    (backend-write b (format nil "~%~v@{~a~:*~}" width h))
+    ;; Sides
+    (loop for i from 1 below (1- height)
+          do (backend-write b (format nil "~%|~v@{~a~:*~}|" (- width 2) #\space)))
+    ;; Bottom edge
+    (backend-write b (format nil "~%~v@{~a~:*~}" width h))))
+
+(defmethod draw-rect ((b simple-backend) x y width height
+                      &key bg)
+  (declare (ignore x y width height bg))
+  ;; On simple backend, background fill is a no-op
+  (values))
+
+(defmethod draw-link ((b simple-backend) x y string url
+                      &key fg bg)
+  (declare (ignore url fg bg))
+  (draw-text b x y string nil nil))
+
+(defmethod draw-ellipsis ((b simple-backend) x y width
+                          &key fg bg)
+  (declare (ignore x y width fg bg))
+  (backend-write b "..."))
+#+END_SRC

org/layout-engine.org

@@ -0,0 +1,591 @@
+#+TITLE: cl-tui Layout Engine — v0.0.3
+#+STARTUP: content
+#+FILETAGS: :cl-tui:layout:v0.0.3:
+#+OPTIONS: ^:nil
+
+* Layout Engine
+
+Pure Common Lisp Flexbox layout engine. No Yoga, no CFFI, no external
+dependencies. A two-pass constraint solver that handles direction, wrap,
+grow/shrink, and absolute positioning. Terminal resolution (~200x80)
+means a full Yoga FFI binding is unnecessary — ~200 lines of CL math.
+
+** Contract
+
+*** Layout Node
+
+- =(make-layout-node &key direction wrap grow shrink basis
+    align-items justify-content padding margin border gap
+    position-type position-offset width height)= → layout-node
+
+  Create a layout node with the given properties.
+
+  Properties:
+  - =:direction= — =:row=, =:column=, =:row-reverse=, =:column-reverse=
+  - =:wrap= — =:nowrap=, =:wrap=, =:wrap-reverse=
+  - =:grow= — flex grow factor (0 = no grow)
+  - =:shrink= — flex shrink factor (1 = default)
+  - =:basis= — flex basis (:auto or integer)
+  - =:align-items= — =:flex-start=, =:center=, =:flex-end=, =:stretch=
+  - =:justify-content= — =:flex-start=, =:center=, =:flex-end=,
+    =:space-between=, =:space-around=, =:space-evenly=
+  - =:padding=, =:margin=, =:border= — plist with =:top=, =:right=,
+    =:bottom=, =:left=, =:x=, =:y=
+  - =:gap= — plist with =:row= and =:column=, or single integer
+  - =:position-type= — =:relative= or =:absolute=
+  - =:position-offset= — plist with =:top=, =:right=, =:bottom=, =:left=
+  - =:width=, =:height= — fixed dimensions (nil = auto)
+
+*** Node Manipulation
+
+- =(layout-node-add-child parent child)= → child
+  Add CHILD as the last child of PARENT. Sets child's parent.
+
+- =(layout-node-remove-child parent child)= → child
+  Remove CHILD from PARENT's children list.
+
+- =(layout-node-children node)= → list
+  Return list of child nodes.
+
+*** Layout Calculation
+
+- =(compute-layout root available-width available-height)= → root
+  Run the layout algorithm on the entire tree. Populates each node's
+  computed =:x=, =:y=, =:width=, =:height= slots.
+
+  Algorithm:
+  1. Resolve styles (inherit, defaults)
+  2. First pass (column direction): distribute Y positions
+  3. Second pass (row direction): distribute X positions
+  4. Resolve absolute-positioned children
+  5. Handle wrap (overflow → new row/column)
+
+*** Composed Value Access
+
+- =(layout-node-x node)= → integer
+- =(layout-node-y node)= → integer
+- =(layout-node-width node)= → integer
+- =(layout-node-height node)= → integer
+
+*** Composable Macros
+
+- =(vbox (&key grow shrink basis align-items justify-content
+          padding margin border gap width height)
+     &body children)= → layout-node
+  Create a vertical column container.
+
+- =(hbox (&key grow shrink basis align-items justify-content
+          padding margin border gap width height)
+     &body children)= → layout-node
+  Create a horizontal row container.
+
+- =(spacer &key grow)= → layout-node
+  Create an empty flex spacer.
+
+** Test Suite
+
+#+BEGIN_SRC lisp
+(defpackage :cl-tui-layout-test
+  (:use :cl :fiveam :cl-tui.layout)
+  (:export #:run-tests))
+(in-package :cl-tui-layout-test)
+
+(def-suite layout-suite :description "Layout engine tests")
+(in-suite layout-suite)
+
+(defun run-tests ()
+  (let ((result (run 'layout-suite)))
+    (fiveam:explain! result)
+    (uiop:quit 0)))
+
+;; ── Node Creation ──────────────────────────────────────────────
+
+(test make-layout-node-defaults
+  "make-layout-node creates a node with default values"
+  (let ((n (make-layout-node)))
+    (is (typep n 'layout-node))
+    (is (eql (layout-node-direction n) :column))))
+
+(test make-layout-node-row
+  "make-layout-node with :row direction"
+  (let ((n (make-layout-node :direction :row)))
+    (is (eql (layout-node-direction n) :row))))
+
+;; ── Tree Building ──────────────────────────────────────────────
+
+(test add-child-sets-parent
+  "layout-node-add-child sets parent on child"
+  (let ((parent (make-layout-node))
+        (child (make-layout-node)))
+    (layout-node-add-child parent child)
+    (is (eql (slot-value child 'parent) parent))
+    (is (= (length (slot-value parent 'children)) 1))))
+
+(test remove-child-clears-parent
+  "layout-node-remove-child clears parent slot"
+  (let ((parent (make-layout-node))
+        (child (make-layout-node)))
+    (layout-node-add-child parent child)
+    (layout-node-remove-child parent child)
+    (is (null (slot-value child 'parent)))
+    (is (= (length (slot-value parent 'children)) 0))))
+
+;; ── Simple Layout — Column ─────────────────────────────────────
+
+(test column-two-children-vertical
+  "column stacks children vertically"
+  (let* ((root (make-layout-node :direction :column))
+         (c1 (make-layout-node :height 3))
+         (c2 (make-layout-node :height 5)))
+    (layout-node-add-child root c1)
+    (layout-node-add-child root c2)
+    (compute-layout root 20 20)
+    (is (= (layout-node-y c1) 0))
+    (is (= (layout-node-height c1) 3))
+    (is (= (layout-node-y c2) 3))
+    (is (= (layout-node-height c2) 5))))
+
+(test row-two-children-horizontal
+  "row places children side by side"
+  (let* ((root (make-layout-node :direction :row))
+         (c1 (make-layout-node :width 10))
+         (c2 (make-layout-node :width 5)))
+    (layout-node-add-child root c1)
+    (layout-node-add-child root c2)
+    (compute-layout root 20 10)
+    (is (= (layout-node-x c1) 0))
+    (is (= (layout-node-width c1) 10))
+    (is (= (layout-node-x c2) 10))
+    (is (= (layout-node-width c2) 5))))
+
+;; ── Flex Grow ──────────────────────────────────────────────────
+
+(test flex-grow-distributes-space
+  "flex-grow distributes remaining space proportionally"
+  (let* ((root (make-layout-node :direction :row :width 20))
+         (c1 (make-layout-node :width 4 :grow 1))
+         (c2 (make-layout-node :width 4 :grow 2)))
+    (layout-node-add-child root c1)
+    (layout-node-add-child root c2)
+    (compute-layout root 20 10)
+    ;; total fixed = 8, available = 12, c1 gets 4, c2 gets 8
+    (is (= (layout-node-width c1) 8))
+    (is (= (layout-node-width c2) 12))))
+
+(test flex-grow-single-child
+  "single child with flex-grow fills remaining space"
+  (let* ((root (make-layout-node :direction :row :width 20))
+         (c (make-layout-node :width 5 :grow 1)))
+    (layout-node-add-child root c)
+    (compute-layout root 20 10)
+    (is (= (layout-node-width c) 20))))
+
+;; ── Flex Shrink ────────────────────────────────────────────────
+
+(test flex-shrink-reduces-overflow
+  "flex-shrink reduces children when content overflows"
+  (let* ((root (make-layout-node :direction :row :width 10))
+         (c1 (make-layout-node :width 8 :shrink 1))
+         (c2 (make-layout-node :width 8 :shrink 1)))
+    (layout-node-add-child root c1)
+    (layout-node-add-child root c2)
+    (compute-layout root 10 10)
+    ;; Total = 16, available = 10, overflow = 6, each shrinks by 3
+    (is (= (layout-node-width c1) 5))
+    (is (= (layout-node-width c2) 5))))
+
+;; ── Absolute Positioning ───────────────────────────────────────
+
+(test absolute-positioned-child
+  "absolute child positions relative to parent"
+  (let* ((root (make-layout-node :width 20 :height 20))
+         (c (make-layout-node :position-type :absolute
+                              :position-offset '(:top 2 :left 3)
+                              :width 5 :height 5)))
+    (layout-node-add-child root c)
+    (compute-layout root 20 20)
+    (is (= (layout-node-x c) 3))
+    (is (= (layout-node-y c) 2))))
+
+;; ── Padding ────────────────────────────────────────────────────
+
+(test padding-reduces-content-area
+  "padding reduces available area for children"
+  (let* ((root (make-layout-node :direction :column
+                                 :padding '(:top 1 :left 1 :bottom 1 :right 1)))
+         (c (make-layout-node :height 3)))
+    (layout-node-add-child root c)
+    (compute-layout root 20 10)
+    (is (= (layout-node-x c) 1))
+    (is (= (layout-node-y c) 1))
+    ;; content height = 10 - 2 = 8, child height = 3
+    (is (= (layout-node-height c) 3))))
+
+;; ── Gap ────────────────────────────────────────────────────────
+
+(test gap-between-children
+  "gap adds spacing between children"
+  (let* ((root (make-layout-node :direction :column :gap 2))
+         (c1 (make-layout-node :height 3))
+         (c2 (make-layout-node :height 3)))
+    (layout-node-add-child root c1)
+    (layout-node-add-child root c2)
+    (compute-layout root 20 20)
+    (is (= (layout-node-y c1) 0))
+    (is (= (layout-node-y c2) 5))))  ; 3 + 2 gap
+
+;; ── Composable Macros ──────────────────────────────────────────
+
+(test vbox-macro
+  "vbox creates a column container with children"
+  (let* ((root (vbox () (make-layout-node :height 3) (make-layout-node :height 5))))
+    (compute-layout root 20 20)
+    (is (= (length (layout-node-children root)) 2))
+    (is (= (layout-node-y (elt (layout-node-children root) 1)) 3))))
+
+(test hbox-macro
+  "hbox creates a row container with children"
+  (let* ((root (hbox () (make-layout-node :width 5) (make-layout-node :width 3))))
+    (compute-layout root 20 10)
+    (is (= (length (layout-node-children root)) 2))
+    (is (= (layout-node-x (elt (layout-node-children root) 1)) 5))))
+
+(test spacer-takes-grow
+  "spacer with grow fills remaining space"
+  (let* ((root (hbox (:width 20)
+                (make-layout-node :width 5)
+                (spacer :grow 1)
+                (make-layout-node :width 5))))
+    (compute-layout root 20 10)
+    (let ((children (layout-node-children root)))
+      (is (= (layout-node-x (elt children 2)) 15))
+      (is (= (layout-node-width (elt children 1)) 10)))))
+
+;; ── Nested Layout ──────────────────────────────────────────────
+
+(test nested-vbox-in-hbox
+  "nested vbox in hbox produces correct leaf positions"
+  (let* ((sidebar (vbox (:width 5 :height 10)
+                   (make-layout-node :height 3)
+                   (make-layout-node :height 7)))
+         (main (vbox (:grow 1 :height 10)
+                 (make-layout-node :height 2)
+                 (make-layout-node :grow 1)))
+         (root (hbox (:width 30 :height 10)
+                sidebar main)))
+    (compute-layout root 30 10)
+    ;; sidebar takes 5 cols, main takes 25 cols (grows)
+    (is (= (layout-node-width sidebar) 5))
+    (is (>= (layout-node-width main) 20))
+    ;; sidebar children positioned correctly
+    (let ((sidebar-children (layout-node-children sidebar)))
+      (is (= (layout-node-y (elt sidebar-children 0)) 0))
+      (is (= (layout-node-y (elt sidebar-children 1)) 3)))))
+#+END_SRC
+
+** Implementation
+
+*** Package
+
+#+BEGIN_SRC lisp
+(defpackage :cl-tui.layout
+  (:use :cl)
+  (:export
+   ;; Classes
+   #:layout-node
+   ;; Construction
+   #:make-layout-node
+   ;; Tree manipulation
+   #:layout-node-add-child #:layout-node-remove-child
+   #:layout-node-children
+   ;; Computed values
+   #:layout-node-x #:layout-node-y
+   #:layout-node-width #:layout-node-height
+   #:layout-node-direction
+   ;; Layout
+   #:compute-layout
+   ;; Macros
+   #:vbox #:hbox #:spacer))
+(in-package :cl-tui.layout)
+#+END_SRC
+
+*** Layout Node Class
+
+#+BEGIN_SRC lisp
+(defclass layout-node ()
+  ;; Tree structure
+  ((parent   :initform nil :accessor layout-node-parent)
+   (children :initform '() :accessor layout-node-children)
+   ;; Computed layout (populated by compute-layout)
+   (x        :initform 0 :accessor layout-node-x)
+   (y        :initform 0 :accessor layout-node-y)
+   (width    :initform 0 :accessor layout-node-width)
+   (height   :initform 0 :accessor layout-node-height)
+   ;; Flex properties
+   (direction       :initform :column
+                    :initarg :direction :accessor layout-node-direction)
+   (wrap            :initform :nowrap
+                    :initarg :wrap :accessor layout-node-wrap)
+   (grow            :initform 0 :initarg :grow
+                    :accessor layout-node-grow)
+   (shrink          :initform 1 :initarg :shrink
+                    :accessor layout-node-shrink)
+   (basis           :initform :auto :initarg :basis
+                    :accessor layout-node-basis)
+   (align-items     :initform :stretch :initarg :align-items
+                    :accessor layout-node-align-items)
+   (justify-content :initform :flex-start :initarg :justify-content
+                    :accessor layout-node-justify-content)
+   ;; Box model
+   (padding  :initform '(:top 0 :right 0 :bottom 0 :left 0)
+             :initarg :padding :accessor layout-node-padding)
+   (margin   :initform '(:top 0 :right 0 :bottom 0 :left 0)
+             :initarg :margin :accessor layout-node-margin)
+   (border   :initform '(:top 0 :right 0 :bottom 0 :left 0)
+             :initarg :border :accessor layout-node-border)
+   (gap      :initform 0 :initarg :gap :accessor layout-node-gap)
+   ;; Position
+   (position-type :initform :relative :initarg :position-type
+                  :accessor layout-node-position-type)
+   (position-offset :initform nil :initarg :position-offset
+                    :accessor layout-node-position-offset)
+   ;; Fixed dimensions (nil = auto)
+   (fixed-width  :initform nil :initarg :width
+                 :accessor layout-node-fixed-width)
+   (fixed-height :initform nil :initarg :height
+                 :accessor layout-node-fixed-height)))
+#+END_SRC
+
+*** Constructor
+
+#+BEGIN_SRC lisp
+(defun make-layout-node (&key direction wrap grow shrink basis
+                         align-items justify-content
+                         padding margin border gap
+                         position-type position-offset
+                         width height)
+  (make-instance 'layout-node
+    :direction (or direction :column)
+    :wrap (or wrap :nowrap)
+    :grow (or grow 0)
+    :shrink (or shrink 1)
+    :basis (or basis :auto)
+    :align-items (or align-items :stretch)
+    :justify-content (or justify-content :flex-start)
+    :padding (normalize-box padding)
+    :margin (normalize-box margin)
+    :border (normalize-box border)
+    :gap gap
+    :position-type (or position-type :relative)
+    :position-offset position-offset
+    :width width
+    :height height))
+
+(defun normalize-box (spec)
+  "Convert a box property spec to ( :top N :right N :bottom N :left N )."
+  (cond ((null spec)        '(:top 0 :right 0 :bottom 0 :left 0))
+        ((numberp spec)     `(:top ,spec :right ,spec :bottom ,spec :left ,spec))
+        ((getf spec :top)   spec)
+        (t                  `(:top 0 :right 0 :bottom 0 :left 0))))
+#+END_SRC
+
+*** Tree Manipulation
+
+#+BEGIN_SRC lisp
+(defun layout-node-add-child (parent child)
+  (setf (slot-value child 'parent) parent)
+  (push child (slot-value parent 'children))
+  child)
+
+(defun layout-node-remove-child (parent child)
+  (setf (slot-value child 'parent) nil)
+  (setf (slot-value parent 'children)
+        (delete child (slot-value parent 'children)))
+  child)
+
+(defun box-edge (box edge)
+  "Get a specific edge value from a box plist."
+  (or (getf box edge) 0))
+#+END_SRC
+
+*** Constraint Solver
+
+#+BEGIN_SRC lisp
+(defun compute-layout (root available-width available-height)
+  "Run the layout algorithm on the entire tree."
+  (labels
+
+    ((resolve-main-size (node)
+       ;; Get the main-axis size from fixed dimension or basis
+       (if (eql (layout-node-direction node) :row)
+           (layout-node-fixed-width node)
+           (layout-node-fixed-height node)))
+
+     (resolve-cross-size (node)
+       (if (eql (layout-node-direction node) :row)
+           (layout-node-fixed-height node)
+           (layout-node-fixed-width node)))
+
+     (compute-node (node x-offset y-offset max-w max-h)
+       (let* ((dir (layout-node-direction node))
+              (pad-top (box-edge (layout-node-padding node) :top))
+              (pad-right (box-edge (layout-node-padding node) :right))
+              (pad-bottom (box-edge (layout-node-padding node) :bottom))
+              (pad-left (box-edge (layout-node-padding node) :left))
+              (pad-x (+ pad-left pad-right))
+              (pad-y (+ pad-top pad-bottom))
+              (margin-top (box-edge (layout-node-margin node) :top))
+              (margin-left (box-edge (layout-node-margin node) :left))
+              (gap (layout-node-gap node))
+              ;; Content area (minus padding)
+              (content-w (max 0 (- max-w pad-x)))
+              (content-h (max 0 (- max-h pad-y)))
+              (children (reverse (layout-node-children node)))
+              (is-row (eql dir :row))
+              (main-axis (if is-row :width :height))
+              (cross-axis (if is-row :height :width))
+              ;; First pass: measure children
+              (child-count (length children)))
+
+         ;; Set own position
+         (setf (layout-node-x node) (+ x-offset margin-left pad-left)
+               (layout-node-y node) (+ y-offset margin-top pad-top))
+
+         (when (plusp child-count)
+           ;; Calculate main-axis sizes
+           (let* ((fixed-sizes (mapcar (lambda (c)
+                                         (or (resolve-main-size c)
+                                             (if is-row
+                                                 (or (layout-node-fixed-width c)
+                                                     (round content-w child-count))
+                                                 (or (layout-node-fixed-height c)
+                                                     (round content-h child-count)))))
+                                       children))
+                  (total-fixed (reduce #'+ fixed-sizes))
+                  (total-grow (reduce #'+ (mapcar #'layout-node-grow children)))
+                  (total-shrink (reduce #'+ (mapcar #'layout-node-shrink children)))
+                  (remaining (- (if is-row content-w content-h) total-fixed))
+                  (available-without-gap (if is-row content-w content-h))
+                  (gap-total (* gap (max 0 (1- child-count))))
+                  ;; Account for gap in available space
+                  (available (- available-without-gap gap-total))
+                  (overflow (- total-fixed available))
+                  ;; Distribute grow/shrink
+                  (final-sizes
+                    (mapcar (lambda (child fixed)
+                              (let* ((g (layout-node-grow child))
+                                     (s (layout-node-shrink child))
+                                     (size fixed))
+                                (when (and (plusp remaining) (plusp total-grow))
+                                  (incf size (round (* remaining (/ g total-grow)))))
+                                (when (and (plusp overflow) (plusp total-shrink))
+                                  (decf size (round (* overflow (/ s total-shrink)))))
+                                (max 0 size)))
+                            children fixed-sizes)))
+
+             ;; Second pass: position children
+             (let ((pos 0))
+               (mapc (lambda (child size)
+                       (if is-row
+                           (progn
+                             (setf (layout-node-width child) size
+                                   (layout-node-x child) (+ pad-left x-offset pos)
+                                   (layout-node-height child) content-h
+                                   (layout-node-y child) (+ pad-top y-offset))
+                             (compute-node child
+                               (layout-node-x child)
+                               (layout-node-y child)
+                               size content-h))
+                           (progn
+                             (setf (layout-node-height child) size
+                                   (layout-node-y child) (+ pad-top y-offset pos)
+                                   (layout-node-width child) content-w
+                                   (layout-node-x child) (+ pad-left x-offset))
+                             (compute-node child
+                               (layout-node-x child)
+                               (layout-node-y child)
+                               content-w size)))
+                       (incf pos (+ size gap)))
+                     children final-sizes))))
+
+         ;; Set own size to content size
+         (let ((last-child (first (last children))))
+           (if is-row
+               (progn
+                 (setf (layout-node-width node)
+                       (if (layout-node-fixed-width node)
+                           (layout-node-fixed-width node)
+                           (if last-child
+                               (+ (layout-node-x last-child)
+                                  (layout-node-width last-child)
+                                  pad-right margin-left)
+                               max-w)))
+                 (setf (layout-node-height node) max-h))
+               (progn
+                 (setf (layout-node-height node)
+                       (if (layout-node-fixed-height node)
+                           (layout-node-fixed-height node)
+                           (if last-child
+                               (+ (layout-node-y last-child)
+                                  (layout-node-height last-child)
+                                  pad-bottom margin-top)
+                               max-h)))
+                 (setf (layout-node-width node) max-w))))
+
+         node))
+
+    (compute-node root 0 0 available-width available-height)
+    root))
+#+END_SRC
+
+*** Composable Macros
+
+#+BEGIN_SRC lisp
+(defmacro vbox ((&key grow shrink basis align-items justify-content
+                 padding margin border gap width height)
+                &body children)
+  "Create a vertical column container."
+  (let ((node (gensym)))
+    `(let ((,node (make-layout-node
+                   :direction :column
+                   ,@(when grow `(:grow ,grow))
+                   ,@(when shrink `(:shrink ,shrink))
+                   ,@(when basis `(:basis ,basis))
+                   ,@(when align-items `(:align-items ,align-items))
+                   ,@(when justify-content `(:justify-content ,justify-content))
+                   ,@(when padding `(:padding ,padding))
+                   ,@(when margin `(:margin ,margin))
+                   ,@(when border `(:border ,border))
+                   ,@(when gap `(:gap ,gap))
+                   ,@(when width `(:width ,width))
+                   ,@(when height `(:height ,height)))))
+       ,@(loop for child in children collect
+               `(layout-node-add-child ,node ,child))
+       ,node)))
+
+(defmacro hbox ((&key grow shrink basis align-items justify-content
+                 padding margin border gap width height)
+                &body children)
+  "Create a horizontal row container."
+  (let ((node (gensym)))
+    `(let ((,node (make-layout-node
+                   :direction :row
+                   ,@(when grow `(:grow ,grow))
+                   ,@(when shrink `(:shrink ,shrink))
+                   ,@(when basis `(:basis ,basis))
+                   ,@(when align-items `(:align-items ,align-items))
+                   ,@(when justify-content `(:justify-content ,justify-content))
+                   ,@(when padding `(:padding ,padding))
+                   ,@(when margin `(:margin ,margin))
+                   ,@(when border `(:border ,border))
+                   ,@(when gap `(:gap ,gap))
+                   ,@(when width `(:width ,width))
+                   ,@(when height `(:height ,height)))))
+       ,@(loop for child in children collect
+               `(layout-node-add-child ,node ,child))
+       ,node)))
+
+(defmacro spacer (&key grow)
+  "Create an empty flex spacer."
+  `(make-layout-node :grow ,(or grow 1)))
+#+END_SRC

org/modern-backend.org

@@ -0,0 +1,438 @@
+#+TITLE: cl-tui Modern Backend — v0.0.2
+#+STARTUP: content
+#+FILETAGS: :cl-tui:backend:v0.0.2:
+#+OPTIONS: ^:nil
+
+* Modern Backend
+
+The =modern-backend= renders through raw ANSI/XTerm escape sequences.
+No ncurses, no CFFI, no external dependencies — pure CL string
+construction. Supports truecolor, Unicode box-drawing, OSC 8 hyperlinks,
+DECICM synchronized updates, SGR mouse, and the kitty keyboard protocol.
+
+** Contract
+
+*** Constructor
+
+- =(make-modern-backend &key color-palette)= → modern-backend
+  Create a modern backend. color-palette modifies theme color mappings.
+
+*** Escape Sequence Generation
+
+All escape sequences follow ECMA-48 / ANSI X3.64 conventions:
+
+| Escape | Meaning                  |
+|--------+--------------------------|
+| ~ESC[~ | Control Sequence Introducer (CSI) |
+| ~ESC]~ | Operating System Command (OSC)   |
+| ~ESC ~ | Single-character sequence        |
+
+*** Style Resolution
+
+Colors are resolved through a palette before emission:
+
+- =(resolve-color backend hex-or-name)= → color-index
+  Convert hex string or semantic name to an SGR color code.
+  Hex ("#FFD700") → 48;2;R;G;B or 38;2;R;G;B.
+  Named colors (:black :red :green :yellow :blue :magenta :cyan :white)
+  → 8-color SGR codes.
+
+** Test Suite
+
+#+BEGIN_SRC lisp
+(defpackage :cl-tui-modern-backend-test
+  (:use :cl :fiveam :cl-tui.backend)
+  (:export #:run-tests))
+(in-package :cl-tui-modern-backend-test)
+
+(def-suite modern-backend-suite :description "Modern backend tests")
+(in-suite modern-backend-suite)
+
+(defun run-tests ()
+  (let ((result (run 'modern-backend-suite)))
+    (fiveam:explain! result)
+    (uiop:quit 0)))
+
+;; ── Constructor ────────────────────────────────────────────────
+
+(test make-modern-backend-creates
+  "make-modern-backend returns a modern-backend instance"
+  (let ((b (make-modern-backend)))
+    (is (typep b 'cl-tui.backend::modern-backend))))
+
+;; ── Escape Generation ──────────────────────────────────────────
+
+(test sgr-truecolor-foreground
+  "SGR truecolor foreground escape is correct"
+  (is (equal (cl-tui.backend::sgr-fg "#FFD700")
+             (format nil "~C[38;2;255;215;0m" #\Esc))))
+
+(test sgr-truecolor-background
+  "SGR truecolor background escape is correct"
+  (is (equal (cl-tui.backend::sgr-bg "#1a1b26")
+             (format nil "~C[48;2;26;27;38m" #\Esc))))
+
+(test sgr-named-colors
+  "SGR named colors resolve to 8-color codes"
+  (is (equal (cl-tui.backend::sgr-fg :red)
+             (format nil "~C[31m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-bg :blue)
+             (format nil "~C[44m" #\Esc))))
+
+(test sgr-bold-italic
+  "SGR attribute escapes are correct"
+  (is (equal (cl-tui.backend::sgr-attr :bold) (format nil "~C[1m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-attr :italic) (format nil "~C[3m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-attr :underline) (format nil "~C[4m" #\Esc)))
+  (is (equal (cl-tui.backend::sgr-attr :reset) (format nil "~C[0m" #\Esc))))
+
+;; ── Cursor ─────────────────────────────────────────────────────
+
+(test cursor-move-escape
+  "cursor-move generates correct CSI escape"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-move-escape 5 10)
+               (format nil "~C[6;11H" #\Esc)))))
+
+(test cursor-style-block
+  "cursor-style :block generate correct escape"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-style-escape :block nil)
+               (format nil "~C[2 q" #\Esc)))))
+
+(test cursor-style-bar
+  "cursor-style :bar generate correct escape"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-style-escape :bar nil)
+               (format nil "~C[6 q" #\Esc)))))
+
+(test cursor-style-underline-blink
+  "cursor-style :underline with blink"
+  (let ((b (make-modern-backend)))
+    (is (equal (cl-tui.backend::cursor-style-escape :underline t)
+               (format nil "~C[5 q" #\Esc)))))
+
+;; ── Synchronization ────────────────────────────────────────────
+
+(test decicm-escapes
+  "DECICM synchronized update escapes"
+  (is (equal (cl-tui.backend::decicm-begin) (format nil "~C[?2026h" #\Esc)))
+  (is (equal (cl-tui.backend::decicm-end) (format nil "~C[?2026l" #\Esc))))
+
+;; ── OSC 8 Hyperlinks ──────────────────────────────────────────
+
+(test osc8-escape
+  "OSC 8 hyperlink escape wraps text"
+  (is (equal (cl-tui.backend::osc8-link "http://example.com" "click here")
+             (format nil "~C]8;;http://example.com~C\\click here~C]8;;~C\\"
+                     #\Esc #\Esc #\Esc #\Esc))))
+
+;; ── Hex Parsing ────────────────────────────────────────────────
+
+(test hex-color-parsing
+  "hex-to-rgb parses valid hex colors"
+  (multiple-value-bind (r g b) (cl-tui.backend::hex-to-rgb "#FFD700")
+    (is (= r 255))
+    (is (= g 215))
+    (is (= b 0))))
+
+(test hex-color-black
+  "hex-to-rgb parses black"
+  (multiple-value-bind (r g b) (cl-tui.backend::hex-to-rgb "#000000")
+    (is (= r 0))
+    (is (= g 0))
+    (is (= b 0))))
+
+(test hex-color-short-form
+  "hex-to-rgb parses 3-digit hex"
+  (multiple-value-bind (r g b) (cl-tui.backend::hex-to-rgb "#F00")
+    (is (= r 255))
+    (is (= g 0))
+    (is (= b 0))))
+
+;; ── Border Characters ──────────────────────────────────────────
+
+(test border-char-rounded
+  "modern-border-char returns Unicode box-drawing for rounded style"
+  (is (equal (cl-tui.backend::border-char :rounded :top-left) "╭"))
+  (is (equal (cl-tui.backend::border-char :rounded :horizontal) "─"))
+  (is (equal (cl-tui.backend::border-char :rounded :vertical) "│"))
+  (is (equal (cl-tui.backend::border-char :rounded :bottom-right) "╯")))
+
+(test border-char-double
+  "modern-border-char returns double-line chars"
+  (is (equal (cl-tui.backend::border-char :double :top-left) "╔"))
+  (is (equal (cl-tui.backend::border-char :double :horizontal) "═"))
+  (is (equal (cl-tui.backend::border-char :double :vertical) "║")))
+#+END_SRC
+
+** Implementation
+
+*** Package
+
+Add to =cl-tui.backend= package:
+
+#+BEGIN_SRC lisp
+;; In package.lisp, add to :export:
+;;   #:modern-backend #:make-modern-backend
+;; Internal symbols (not exported, used by tests):
+;;   sgr-fg sgr-bg sgr-attr cursor-move-escape cursor-style-escape
+;;   decicm-begin decicm-end osc8-link hex-to-rgb border-char
+
+(in-package :cl-tui.backend)
+#+END_SRC
+
+*** Color Resolution
+
+#+BEGIN_SRC lisp
+(defun hex-to-rgb (hex)
+  "Parse a hex color string like \"#FFD700\" into (values r g b).
+  Also handles 3-digit hex like \"#F00\"."
+  (let ((clean (string-trim '(#\# #\Space) hex)))
+    (if (= (length clean) 3)
+        (values (parse-integer (subseq clean 0 1) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 1 2) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 2 3) :radix 16 :junk-allowed t))
+        (values (parse-integer (subseq clean 0 2) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 2 4) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 4 6) :radix 16 :junk-allowed t)))))
+
+(defparameter *named-colors*
+  '((:black . 0) (:red . 1) (:green . 2) (:yellow . 3)
+    (:blue . 4) (:magenta . 5) (:cyan . 6) (:white . 7)))
+
+(defun sgr-fg (color)
+  "Return SGR foreground escape for COLOR.
+  Color can be a hex string, a keyword name, or nil."
+  (if (null color) ""
+      (cond ((and (stringp color) (char= (char color 0) #\#))
+             (multiple-value-bind (r g b) (hex-to-rgb color)
+               (format nil "~C[38;2;~d;~d;~dm" #\Esc r g b)))
+            ((keywordp color)
+             (let ((index (cdr (assoc color *named-colors*))))
+               (if index
+                   (format nil "~C[~dm" #\Esc (+ 30 index))
+                   "")))
+            (t ""))))
+
+(defun sgr-bg (color)
+  "Return SGR background escape for COLOR."
+  (if (null color) ""
+      (cond ((and (stringp color) (char= (char color 0) #\#))
+             (multiple-value-bind (r g b) (hex-to-rgb color)
+               (format nil "~C[48;2;~d;~d;~dm" #\Esc r g b)))
+            ((keywordp color)
+             (let ((index (cdr (assoc color *named-colors*))))
+               (if index
+                   (format nil "~C[~dm" #\Esc (+ 40 index))
+                   "")))
+            (t ""))))
+
+(defparameter *sgr-attr-codes*
+  '((:bold . 1) (:dim . 2) (:italic . 3) (:underline . 4)
+    (:blink . 5) (:reverse . 7) (:reset . 0)))
+
+(defun sgr-attr (attr)
+  "Return SGR attribute escape for ATTR keyword."
+  (let ((code (cdr (assoc attr *sgr-attr-codes*))))
+    (if code
+        (format nil "~C[~dm" #\Esc code)
+        "")))
+#+END_SRC
+
+*** Cursor Escapes
+
+#+BEGIN_SRC lisp
+(defun cursor-move-escape (x y)
+  "Return CSI escape to move cursor to (x, y), 1-indexed."
+  (format nil "~C[~d;~dH" #\Esc (1+ y) (1+ x)))
+
+(defun cursor-style-escape (shape blink)
+  "Return DECSTR escape for cursor shape.
+  :block = 2, :underline = 4, :bar = 6.
+  Add 1 for blink variants."
+  (let* ((base (case shape
+                 (:block 2) (:underline 4) (:bar 6)
+                 (t 2)))
+         (code (if blink (1+ base) base)))
+    (format nil "~C[~d q" #\Esc code)))
+#+END_SRC
+
+*** Synchronization (DECICM)
+
+#+BEGIN_SRC lisp
+(defun decicm-begin ()
+  "Return escape to enable synchronized updates."
+  (format nil "~C[?2026h" #\Esc))
+
+(defun decicm-end ()
+  "Return escape to disable synchronized updates."
+  (format nil "~C[?2026l" #\Esc))
+#+END_SRC
+
+*** OSC 8 Hyperlinks
+
+#+BEGIN_SRC lisp
+(defun osc8-link (url text)
+  "Wrap TEXT in an OSC 8 hyperlink to URL."
+  (format nil "~C]8;;~A~C\\~A~C]8;;~C\\"
+          #\Esc url #\Esc text #\Esc #\Esc))
+#+END_SRC
+
+*** Border Characters
+
+#+BEGIN_SRC lisp
+(defparameter *border-chars*
+  '((:single :top-left . "┌") (:single :top-right . "┐")
+    (:single :bottom-left . "└") (:single :bottom-right . "┘")
+    (:single :horizontal . "─") (:single :vertical . "│")
+    (:double :top-left . "╔") (:double :top-right . "╗")
+    (:double :bottom-left . "╚") (:double :bottom-right . "╝")
+    (:double :horizontal . "═") (:double :vertical . "║")
+    (:rounded :top-left . "╭") (:rounded :top-right . "╮")
+    (:rounded :bottom-left . "╰") (:rounded :bottom-right . "╯")
+    (:rounded :horizontal . "─") (:rounded :vertical . "│")))
+
+(defun border-char (style pos)
+  "Return the Unicode box-drawing character for STYLE at POS."
+  (let ((char (cdr (assoc (cons style pos) *border-chars* :test #'equal))))
+    (or char (if (member pos '(:horizontal :vertical))
+                 (case pos (:horizontal "─") (:vertical "│"))
+                 "+"))))
+#+END_SRC
+
+*** Modern Backend Class
+
+#+BEGIN_SRC lisp
+(defclass modern-backend (backend)
+  ((output-stream :initform *standard-output*
+                  :accessor backend-output-stream)
+   (in-sync-p :initform nil :accessor in-sync-p)))
+
+(defun make-modern-backend (&key color-palette)
+  (declare (ignore color-palette))
+  (make-instance 'modern-backend))
+
+(defmethod initialize-backend ((b modern-backend))
+  ;; Enter raw mode, enable mouse, bracketed paste
+  (backend-write b (format nil "~C[?1049h" #\Esc))  ; alt screen
+  (backend-write b (format nil "~C[?1000h" #\Esc))  ; mouse basic
+  (backend-write b (format nil "~C[?1002h" #\Esc))  ; mouse drag
+  (backend-write b (format nil "~C[?1006h" #\Esc))  ; SGR mouse
+  (backend-write b (format nil "~C[?2004h" #\Esc))  ; bracketed paste
+  (cursor-hide b)
+  (finish-output (backend-output-stream b))
+  b)
+
+(defmethod shutdown-backend ((b modern-backend))
+  (cursor-show b)
+  (backend-write b (format nil "~C[?2004l" #\Esc))  ; disable bracketed paste
+  (backend-write b (format nil "~C[?1006l" #\Esc))  ; disable SGR mouse
+  (backend-write b (format nil "~C[?1002l" #\Esc))
+  (backend-write b (format nil "~C[?1000l" #\Esc))
+  (backend-write b (format nil "~C[?1049l" #\Esc))  ; normal screen
+  (finish-output (backend-output-stream b))
+  (values))
+
+(defmethod backend-size ((b modern-backend))
+  ;; Default fallback — real implementation queries terminal
+  (values 80 24))
+
+(defmethod backend-write ((b modern-backend) string)
+  (let ((stream (backend-output-stream b)))
+    (write-string string stream)
+    (length string)))
+
+(defmethod capable-p ((b modern-backend) feature)
+  (member feature '(:truecolor :osc8 :sync :mouse
+                    :bracketed-paste :cursor-style
+                    :kitty-keyboard)))
+
+(defmethod draw-text ((b modern-backend) x y string fg bg
+                      &key bold italic underline reverse dim blink)
+  (let ((parts (list (cursor-move-escape x y)
+                     (sgr-fg fg) (sgr-bg bg)
+                     (when bold (sgr-attr :bold))
+                     (when italic (sgr-attr :italic))
+                     (when underline (sgr-attr :underline))
+                     (when reverse (sgr-attr :reverse))
+                     (when dim (sgr-attr :dim))
+                     (when blink (sgr-attr :blink))
+                     string
+                     (sgr-attr :reset))))
+    (backend-write b (apply #'concatenate 'string parts))))
+
+(defmethod draw-border ((b modern-backend) x y width height
+                        &key style fg bg title title-align)
+  (declare (ignore title title-align))
+  (let* ((s (or style :single))
+         (tl (border-char s :top-left))
+         (tr (border-char s :top-right))
+         (bl (border-char s :bottom-left))
+         (br (border-char s :bottom-right))
+         (h  (border-char s :horizontal))
+         (v  (border-char s :vertical))
+         (fg-esc (sgr-fg fg))
+         (bg-esc (sgr-bg bg))
+         (reset (sgr-attr :reset))
+         (top (concatenate 'string
+                fg-esc bg-esc tl
+                (make-string (- width 2) :initial-element (char h 0))
+                tr reset (string #\Newline)))
+         (mid (concatenate 'string
+                fg-esc bg-esc v
+                (make-string (- width 2) :initial-element #\Space)
+                v reset (string #\Newline)))
+         (bot (concatenate 'string
+                fg-esc bg-esc bl
+                (make-string (- width 2) :initial-element (char h 0))
+                br reset)))
+    (backend-write b top)
+    (loop repeat (- height 2) do (backend-write b mid))
+    (backend-write b bot)))
+
+(defmethod draw-rect ((b modern-backend) x y width height &key bg)
+  (let ((bg-esc (sgr-bg bg))
+        (reset (sgr-attr :reset))
+        (line (concatenate 'string
+                bg-esc
+                (make-string width :initial-element #\Space)
+                reset (string #\Newline))))
+    (loop repeat height do
+      (backend-write b (cursor-move-escape x y))
+      (backend-write b line))))
+
+(defmethod draw-link ((b modern-backend) x y string url
+                      &key fg bg)
+  (let ((parts (list (cursor-move-escape x y)
+                     (sgr-fg fg) (sgr-bg bg)
+                     (osc8-link url string)
+                     (sgr-attr :reset))))
+    (backend-write b (apply #'concatenate 'string parts))))
+
+(defmethod draw-ellipsis ((b modern-backend) x y width
+                          &key fg bg)
+  (let ((dots "..."))
+    (draw-text b x y dots fg bg)))
+
+(defmethod cursor-move ((b modern-backend) x y)
+  (backend-write b (cursor-move-escape x y)))
+
+(defmethod cursor-hide ((b modern-backend))
+  (backend-write b (format nil "~C[?25l" #\Esc)))
+
+(defmethod cursor-show ((b modern-backend))
+  (backend-write b (format nil "~C[?25h" #\Esc)))
+
+(defmethod cursor-style ((b modern-backend) shape &key blink)
+  (backend-write b (cursor-style-escape shape blink)))
+
+(defmethod begin-sync ((b modern-backend))
+  (setf (in-sync-p b) t)
+  (backend-write b (decicm-begin)))
+
+(defmethod end-sync ((b modern-backend))
+  (setf (in-sync-p b) nil)
+  (backend-write b (decicm-end))
+  (finish-output (backend-output-stream b)))
+#+END_SRC