literate: convert org/layout-engine.org from doc-only to tangle source

Now tangles to layout.lisp + layout/tests.lisp.
Deleted hand-written originals and regenerated — GREEN.

src/layout/layout.lisp

@@ -1,5 +1,3 @@
-;;; layout — Pure CL Flexbox layout engine
-
 (defpackage :cl-tty.layout
   (:use :cl)
   (:export
@@ -15,7 +13,6 @@
    #:layout-node-parent #:layout-node-fixed-width
    #:layout-node-fixed-height #:normalize-box
    #:box-edge))
-
 (in-package :cl-tty.layout)
 
 (defun normalize-box (spec)
@@ -70,14 +67,7 @@
         (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.
-Rounding errors are amortized across the first N children."
   (let* ((n (length children))
          (gap-total (* gap (max 0 (1- n))))
          (base (mapcar (lambda (c)
@@ -98,10 +88,6 @@ Rounding errors are amortized across the first N children."
                                (decf sz (round (* (abs remaining) (/ (layout-node-shrink c) shrink-total)))))
                              (max 1 sz)))
                          children base)))
-      ;; Distribute rounding remainder to first N children so that
-      ;; the total of sizes exactly fills avail minus gap-total.
-      ;; Only correct when grow or shrink was actually applied —
-      ;; otherwise children keep their fixed sizes and may not fill space.
       (when (or (and (plusp remaining) (plusp grow-total))
                 (and (minusp remaining) (plusp shrink-total)))
         (let ((delta (- avail gap-total (reduce #'+ sizes))))
@@ -111,8 +97,6 @@ Rounding errors are amortized across the first N children."
       sizes)))
 
 (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))
@@ -124,10 +108,8 @@ Recursively computes position and size for every node."
                     (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
@@ -146,7 +128,6 @@ Recursively computes position and size for every node."
                                          (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)
@@ -170,8 +151,6 @@ Recursively computes position and size for every node."
     (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