W14: C23 adapter-dom render-output tests (test-only) — section C complete

The DOM adapter's only test file asserts membership predicates ("if is a
render form") — zero tests inspect what render-to-dom actually builds
(hosts.md C23), and the file is excluded from the runner as browser-only.

Discovery: the browser-only assumption is false for render output —
(import (web adapter-dom)) disk-resolves in the OCaml runner and
render-to-dom works against its mock DOM. Add
web/tests/test-adapter-dom-render.sx (8 tests) pinning the adapter's real
output contract (probed first): text renders as a nodeType-3 child text
node; when/map wrap output in a FRAGMENT child; if inlines the chosen
branch; attrs/class/id land on the element; voids have no children.

Auto-included in default runs — first render-output coverage of the
1512-line adapter in the standard gate. Remaining depth (boolean attrs,
on-*/bind/ref/key, reactive attrs, hydration cursor) tracked on the
checklist. 254/0 standalone.

Test-only: no semantics edits, no push.

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

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

@@ -76,7 +76,10 @@ Pin each confirmed-and-fixed finding with a minimal repro. Add suites to
       logging; 5 pins incl. the S10 map-over-perform probe (CEK keeps all
       elements — the drop class is serving-JIT-side). Runner-only (needs
       cek-* driver bindings)
-- [ ] C23 — adapter-dom render-output tests
+- [x] C23 — adapter-dom render-output tests
+      (`web/tests/test-adapter-dom-render.sx`, 8 tests vs runner mock DOM;
+      follow-up depth still open: boolean attrs, on-*/bind/ref/key,
+      reactive attrs, hydration cursor)
 
 ### D. WASM corpus runner
 - [ ] F2 — promote conformance's `run_wasm.js` prototype into CI
@@ -91,6 +94,20 @@ Pin each confirmed-and-fixed finding with a minimal repro. Add suites to
 
 ## Progress log (newest first)
 
+- 2026-07-04 — **C23 adapter-dom render-output tests (item C.4) — section C
+  COMPLETE**. Key discovery: the "browser-only" exclusion of adapter-dom
+  testing is FALSE for render output — `(import (web adapter-dom))`
+  disk-resolves in the OCaml runner and `render-to-dom` works against its
+  mock DOM (dom-* → host-* → mock elements). New
+  `web/tests/test-adapter-dom-render.sx` (8 tests): tag/text-child-node,
+  class+id, ordered children, void element, when-false empty FRAGMENT,
+  when-true branch-in-fragment, map N-children-in-fragment, if inlines
+  branch. Probed the adapter's output contract first (text = nodeType-3
+  child; control flow = FRAGMENT wrapper; if inlines). Auto-included in
+  default runs (not on the exclusion list) — first render-output coverage
+  of the 1512-line adapter in the standard gate. Follow-up depth (boolean
+  attrs, on-*/bind/ref/key, reactive, hydration) noted on the checklist.
+  254/0 standalone. Test-only.
 - 2026-07-04 — **C21 perform-mode harness (item C.3)**. Added
   `harness-run-perform` to spec/harness.sx (exported): drives
   `make-cek-state`/`cek-step-loop`, services each