W14: pin K49 void-elements spec fix; discover sx_render.ml regen drift (test-only)

K49: area/base/embed/param/track were in VOID_ELEMENTS but missing from
HTML_TAGS — render fell through to "Undefined symbol: base". dc7aa709 fixed
spec/render.sx; add suite gate-K49-void-elements-renderable (3 tests): the
spec registry contains all five, and render-to-html renders each as a
self-closing void. 264 passed / 0 failed under OCaml run_tests.

DISCOVERY (recorded in the briefing's Blocked section): the generated
hosts/ocaml/lib/sx_render.ml was never regenerated after the spec fix — its
stale html_tags_list still lacks the five tags, so the runner's native
render-html path STILL errors. Fix is a bootstrap_render.py regen (hosts
lane, out of scope for this test-only loop). Live evidence for F13
(regen-diff CI gate). Pin covers the spec side only for now.

Also corrects the checklist label: K49 = void elements; the depth/cycle
guard is K16 (OPEN, W8).

Test-only: no semantics edits, no push.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

spec/tests/test-gate-pins.sx

@@ -119,3 +119,45 @@
   (deftest
     "do with a single IIFE form returns its value"
     (assert= (do ((fn () 42))) 42)))
+
+;; --------------------------------------------------------------------------
+;; K49 [W8, med] Five void elements (area base embed param track) were in
+;; VOID_ELEMENTS but missing from HTML_TAGS — render fell through to
+;; function-call dispatch: (render-to-html '(base :href "x")) threw
+;; "Undefined symbol: base". dc7aa709 fixed the SPEC registry
+;; (spec/render.sx). NB: the generated OCaml render library
+;; (hosts/ocaml/lib/sx_render.ml, bootstrap_render.py output) still carries
+;; a STALE html_tags_list without these five — the runner's native
+;; `render-html` convenience therefore still errors. That regen drift is
+;; W14 item F13 (regen-diff gate); this suite pins the spec side only.
+;; --------------------------------------------------------------------------
+(defsuite
+  "gate-K49-void-elements-renderable"
+  (deftest
+    "spec HTML_TAGS registry contains all five void elements"
+    (for-each
+      (fn
+        (t)
+        (assert (contains? HTML_TAGS t) (str "HTML_TAGS missing " t)))
+      (list "area" "base" "embed" "param" "track")))
+  (deftest
+    "spec render-to-html renders base self-closing with attr"
+    (assert-equal
+      "<base href=\"x\" />"
+      (render-to-html (quote (base :href "x")) (make-env))))
+  (deftest
+    "spec render-to-html renders all five as self-closing voids"
+    (for-each
+      (fn
+        (form)
+        (let
+          ((html (render-to-html form (make-env))))
+          (assert
+            (string-contains? html "/>")
+            (str (first form) " not self-closing: " html))))
+      (list
+        (quote (area))
+        (quote (base))
+        (quote (embed))
+        (quote (param))
+        (quote (track))))))