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>

plans/agent-briefings/sx-gate-loop.md

@@ -47,7 +47,9 @@ Pin each confirmed-and-fixed finding with a minimal repro. Add suites to
 - [x] K18 [W7] — `expt` overflow now float-promotes (no 63-bit wrap)
 - [x] K20 [W7] — `contains?` now supports dict key membership
 - [x] K09/K11/K39 [W5] — longhand `unquote-splicing`, guard sentinel gensym, `do` IIFE-head
-- [ ] K49 [W8] — render depth/cycle guard (infinite recursive component)
+- [x] K49 [W8] — five void elements (area/base/embed/param/track) renderable
+      (spec side; native regen drift → see Blocked). NB: the depth/cycle guard
+      is K16 [W8], still OPEN — not a W14 pin target until its fix lands
 - [ ] crit-2 [W1] — signal-return frame key (verify the pin is non-vacuous)
 - [ ] C1/C1b [W3] — HTTP-mode concurrency fixes, pin
 - [ ] S4 [conformance] — housekeeping repro, pin
@@ -77,6 +79,18 @@ Pin each confirmed-and-fixed finding with a minimal repro. Add suites to
 
 ## Progress log (newest first)
 
+- 2026-07-03 — **K49 void-elements pin (item A.4) + regen-drift DISCOVERY**.
+  Corrected the checklist label first: K49 is "five void elements
+  unrenderable" (core.md:335), not the depth guard (that's K16, OPEN). Added
+  suite `gate-K49-void-elements-renderable` (3 tests): spec `HTML_TAGS`
+  contains all five; `(render-to-html '(base :href "x") (make-env))` →
+  `<base href="x" />`; all five render self-closing. Runner-env gotchas:
+  `current-env`/`symbol` are not bound in run_tests — use `(make-env)` and
+  literal quoted forms. **Discovery:** the first draft pinned via the
+  runner's native `render-html` and FAILED — `hosts/ocaml/lib/sx_render.ml`
+  (generated) was never regenerated after dc7aa709's spec fix, so the native
+  render path still errors on the five tags. Recorded under Blocked; live
+  evidence for F13 (regen-diff gate). 264 passed / 0 failed. Test-only.
 - 2026-07-03 — **K09/K11/K39 W5 special-form pins (item A.3)**. Three suites
   added to `spec/tests/test-gate-pins.sx`: `gate-K09-longhand-unquote-splicing`
   (R7RS longhand `(unquote-splicing X)` now splices, incl. empty-list case;
@@ -102,4 +116,15 @@ Pin each confirmed-and-fixed finding with a minimal repro. Add suites to
   promotion). Verified 4/4 green under the OCaml run_tests kernel. Test-only.
 
 ## Blocked
-- (none)
+- **K49 native path — sx_render.ml regen drift** (found 2026-07-03 while
+  pinning A.4): dc7aa709 fixed HTML_TAGS in `spec/render.sx` but never re-ran
+  `hosts/ocaml/bootstrap_render.py`, so the generated
+  `hosts/ocaml/lib/sx_render.ml` still carries a stale `html_tags_list`
+  without area/base/embed/param/track. The runner's native `render-html`
+  convenience (and any native fast-path render) therefore STILL throws
+  `Undefined symbol: base` — dc7aa709's "verified on the native binary" claim
+  did not cover this path. Fix = regen (hosts lane, semantics-adjacent — out
+  of scope for this test-only loop). This is a live instance of **F13**
+  (regen-diff CI gate, section-B/D territory): a regen-diff check would have
+  caught it at commit time. The K49 pin covers the spec side only; when the
+  regen lands, extend the suite with `render-html`-path assertions.