Step 17b: Pretext — DOM-free text layout with otfm font measurement

Pure SX text layout library with one IO boundary (text-measure perform).
Knuth-Plass optimal line breaking, Liang's hyphenation, position calculation.

Library (lib/text-layout.sx):
- break-lines: Knuth-Plass DP over word widths
- break-lines-greedy: simple word-wrap for comparison
- hyphenate-word: Liang's trie algorithm
- position-line/position-lines: running x/y sums
- measure-text: single perform (text-measure IO)

Server font measurement (otfm):
- Reads OpenType cmap + hmtx tables from .ttf files
- DejaVu Serif/Sans bundled in shared/static/fonts/
- _cek_io_resolver hook: perform works inside aser/eval_expr
- JIT VM suspension inline resolution for IO in compiled code

~font component (shared/sx/templates/font.sx):
- Works like ~tw: emits @font-face CSS via cssx scope
- Sets font-family on parent via spread
- Deduplicates font declarations

Infrastructure fixes:
- stdin load command: per-expression error handling (was aborting on first error)
- cek_run IO hook: _cek_io_resolver in sx_types.ml
- JIT VmSuspended: inline IO resolution when resolver installed
- ListRef handling in IO resolver (perform creates ListRef, not List)

Demo page at /sx/(applications.(pretext)):
- Hero: justified paragraph with otfm-measured proportional widths
- Greedy vs Knuth-Plass side-by-side comparison
- Badness scoring visualization
- Hyphenation syllable decomposition

25 new tests (spec/tests/test-text-layout.sx), 3201/3201 passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sx/sx/pretext-demo.sx

@@ -1,7 +1,7 @@
 ;; Pretext demo — DOM-free text layout
 ;;
 ;; Visual-first: shows typeset text, then explains how.
-;; Uses measure-text (perform) for real glyph measurement.
+;; Uses measure-text (perform) for glyph measurement.
 
 ;; Compute positioned word data for one line.
 (define
@@ -45,15 +45,6 @@
                     {:y y :words (pretext-position-line lw lwid gap)}))))))
         (range n-lines)))))
 
-;; Measure all words and return widths list
-(define
-  pretext-measure-words
-  (fn
-    (words font size)
-    (map
-      (fn (w) (let ((m (measure-text font size w))) (get m :width)))
-      words)))
-
 ;; Render pre-computed positioned lines
 (defcomp
   ~pretext-demo/render-paragraph
@@ -109,13 +100,23 @@
       (font "serif")
       (size 15))
     (let
-      ((sw (pretext-measure-words sample-words font size))
-        (space-m (measure-text font size " "))
-        (n-words (len sample-words)))
+      ((sw (list)) (n-words (len sample-words)))
+      (for-each
+        (fn
+          (w)
+          (let
+            ((m (measure-text font size w)))
+            (append! sw (get m :width))))
+        sample-words)
       (let
-        ((space-w (get space-m :width)))
+        ((space-m (measure-text font size " "))
+          (space-w (get (measure-text font size " ") :width)))
         (div
-          (~tw :tokens "space-y-10")
+          (begin
+            (~tw :tokens "space-y-10")
+            (~font
+              :family "Pretext Serif"
+              :src "/static/fonts/DejaVuSerif.ttf"))
           (div
             (~tw :tokens "space-y-4")
             (div
@@ -166,11 +167,6 @@
               (div
                 (~tw :tokens "grid grid-cols-1 md:grid-cols-2 gap-4")
                 (~pretext-demo/render-paragraph
-                  :words sample-words
-                  :widths sw
-                  :space-width space-w
-                  :max-width nm
-                  :line-height 22
                   :lines (pretext-layout-lines
                     sample-words
                     sw
@@ -178,14 +174,11 @@
                     space-w
                     nm
                     22)
+                  :max-width nm
+                  :line-height 22
                   :n-words n-words
                   :label "Greedy (browser default)")
                 (~pretext-demo/render-paragraph
-                  :words sample-words
-                  :widths sw
-                  :space-width space-w
-                  :max-width nm
-                  :line-height 22
                   :lines (pretext-layout-lines
                     sample-words
                     sw
@@ -193,6 +186,8 @@
                     space-w
                     nm
                     22)
+                  :max-width nm
+                  :line-height 22
                   :n-words n-words
                   :label "Knuth-Plass optimal"))))
           (div