HS: append command, list stringify as comma-separated

Compiler:
- append to symbol → (set! target (hs-append target value))
- append to DOM → (hs-append! value target)

Runtime:
- hs-append: pure function for string concat and list append
- hs-append!: DOM insertAdjacentHTML for element targets

Mock DOM:
- dom_stringify handles List by joining elements with commas
  (matching JS Array.toString() behavior)

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

lib/hyperscript/runtime.sx

@@ -393,16 +393,29 @@
                 (true (do-loop (rest remaining))))))))
       (do-loop items))))
 
+(begin
+  (define
+    hs-append
+    (fn
+      (target value)
+      (cond
+        ((string? target) (str target value))
+        ((list? target) (append target (list value)))
+        (true (str target value)))))
+  (define
+    hs-append!
+    (fn (value target) (dom-insert-adjacent-html target "beforeend" value))))
+
+
+
+
+
 (define
   hs-fetch
   (fn
     (url format)
     (perform (list "io-fetch" url (if format format "text")))))
 
-
-
-
-
 (define
   hs-coerce
   (fn
@@ -491,7 +504,8 @@
           (map (fn (k) (list k (get value k))) (keys value))
           value))
       (true value))))
-
+;; ── Sandbox/test runtime additions ──────────────────────────────
+;; Property access — dot notation and .length
 (define
   hs-add
   (fn
@@ -501,8 +515,7 @@
       ((list? b) (cons a b))
       ((or (string? a) (string? b)) (str a b))
       (true (+ a b)))))
-;; ── Sandbox/test runtime additions ──────────────────────────────
-;; Property access — dot notation and .length
+;; DOM query stub — sandbox returns empty list
 (define
   hs-make
   (fn
@@ -513,15 +526,15 @@
       ((= type-name "Set") (list))
       ((= type-name "Map") (dict))
       (true (dict)))))
-;; DOM query stub — sandbox returns empty list
-(define hs-install (fn (behavior-fn) (behavior-fn me)))
 ;; Method dispatch — obj.method(args)
-(define
-  hs-measure
-  (fn (target) (perform (list (quote io-measure) target))))
+(define hs-install (fn (behavior-fn) (behavior-fn me)))
 
 ;; ── 0.9.90 features ─────────────────────────────────────────────
 ;; beep! — debug logging, returns value unchanged
+(define
+  hs-measure
+  (fn (target) (perform (list (quote io-measure) target))))
+;; Property-based is — check obj.key truthiness
 (define
   hs-transition
   (fn
@@ -534,7 +547,7 @@
         (str prop " " (/ duration 1000) "s")))
     (dom-set-style target prop value)
     (when duration (hs-settle target))))
-;; Property-based is — check obj.key truthiness
+;; Array slicing (inclusive both ends)
 (define
   hs-transition-from
   (fn
@@ -548,7 +561,7 @@
         (str prop " " (/ duration 1000) "s")))
     (dom-set-style target prop (str to-val))
     (when duration (hs-settle target))))
-;; Array slicing (inclusive both ends)
+;; Collection: sorted by
 (define
   hs-type-check
   (fn
@@ -568,21 +581,21 @@
             (= (host-typeof value) "element")
             (= (host-typeof value) "text")))
         (true (= (host-typeof value) (downcase type-name)))))))
-;; Collection: sorted by
+;; Collection: sorted by descending
 (define
   hs-type-check-strict
   (fn
     (value type-name)
     (if (nil? value) false (hs-type-check value type-name))))
-;; Collection: sorted by descending
+;; Collection: split by
 (define
   hs-strict-eq
   (fn (a b) (and (= (type-of a) (type-of b)) (= a b))))
-;; Collection: split by
+;; Collection: joined by
 (define
   hs-eq-ignore-case
   (fn (a b) (= (downcase (str a)) (downcase (str b)))))
-;; Collection: joined by
+
 (define
   hs-starts-with-ic?
   (fn (str prefix) (starts-with? (downcase str) (downcase prefix))))