diff --git a/plans/agent-briefings/sx-gate-loop.md b/plans/agent-briefings/sx-gate-loop.md
index 5a9a8f0d..29c1a97e 100644
--- a/plans/agent-briefings/sx-gate-loop.md
+++ b/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
diff --git a/web/tests/test-adapter-dom-render.sx b/web/tests/test-adapter-dom-render.sx
new file mode 100644
index 00000000..646c7eff
--- /dev/null
+++ b/web/tests/test-adapter-dom-render.sx
@@ -0,0 +1,93 @@
+;; ==========================================================================
+;; test-adapter-dom-render.sx — C23 (W14): actual render-OUTPUT tests for
+;; the DOM adapter. The pre-existing test-adapter-dom.sx asserts membership
+;; predicates only ("if is a render form") — zero tests inspected what
+;; render-to-dom actually builds, leaving the 1512-line adapter the
+;; thinnest-tested relative to size (hosts.md C23).
+;;
+;; Runs against the OCaml runner's mock DOM (host-* primitives) through the
+;; real (web adapter-dom) library, disk-resolved by import.
+;;
+;; Adapter output contract (probed 2026-07-04):
+;;   - text renders as a CHILD TEXT NODE (nodeType 3, textContent set);
+;;     the parent's own textContent prop stays "" in the mock
+;;   - control-flow forms (when/map/...) wrap their output in a FRAGMENT
+;;     child; `if` inlines the chosen branch directly
+;; ==========================================================================
+(import (web adapter-dom))
+
+(defsuite
+  "adapter-dom-render-output"
+  (deftest
+    "simple element: tag, text child node"
+    (let
+      ((el (render-to-dom (quote (div "hello")) (make-env))))
+      (assert= (dom-node-name el) "DIV")
+      (let
+        ((kids (dom-get-prop el "children")))
+        (assert= (len kids) 1)
+        (assert= (dom-get-prop (first kids) "nodeType") 3)
+        (assert= (dom-text-content (first kids)) "hello"))))
+  (deftest
+    "class and id land on the element"
+    (let
+      ((el (render-to-dom (quote (div :class "card" :id "main" "x")) (make-env))))
+      (assert= (dom-get-prop el "className") "card")
+      (assert
+        (or
+          (= (dom-get-prop el "id") "main")
+          (= (get (dom-get-prop el "attributes") "id") "main"))
+        "id not set as prop or attribute")))
+  (deftest
+    "nested children are appended in order"
+    (let
+      ((el (render-to-dom (quote (ul (li "a") (li "b") (li "c"))) (make-env))))
+      (let
+        ((kids (dom-get-prop el "children")))
+        (assert= (len kids) 3)
+        (assert= (dom-node-name (first kids)) "LI")
+        (assert=
+          (dom-text-content
+            (first (dom-get-prop (nth kids 2) "children")))
+          "c"))))
+  (deftest
+    "void element renders with no children"
+    (let
+      ((el (render-to-dom (quote (input :type "text")) (make-env))))
+      (assert= (dom-node-name el) "INPUT")
+      (assert= (len (dom-get-prop el "children")) 0)))
+  (deftest
+    "when false yields an empty fragment"
+    (let
+      ((el (render-to-dom (quote (div (when false (span "hidden")))) (make-env))))
+      (let
+        ((kids (dom-get-prop el "children")))
+        (assert= (len kids) 1)
+        (assert= (dom-node-name (first kids)) "FRAGMENT")
+        (assert= (len (dom-get-prop (first kids) "children")) 0))))
+  (deftest
+    "when true renders the branch inside its fragment"
+    (let
+      ((el (render-to-dom (quote (div (when true (span "shown")))) (make-env))))
+      (let
+        ((frag (first (dom-get-prop el "children"))))
+        (assert= (dom-node-name frag) "FRAGMENT")
+        (assert=
+          (dom-node-name (first (dom-get-prop frag "children")))
+          "SPAN"))))
+  (deftest
+    "map render form produces one child per element inside its fragment"
+    (let
+      ((el (render-to-dom (quote (ul (map (fn (x) (li x)) (list "1" "2" "3")))) (make-env))))
+      (let
+        ((frag (first (dom-get-prop el "children"))))
+        (assert= (dom-node-name frag) "FRAGMENT")
+        (let
+          ((items (dom-get-prop frag "children")))
+          (assert= (len items) 3)
+          (assert= (dom-node-name (first items)) "LI")))))
+  (deftest
+    "if render form inlines the chosen branch directly"
+    (let
+      ((el (render-to-dom (quote (div (if true (b "yes") (i "no")))) (make-env))))
+      (assert= (dom-node-name (first (dom-get-prop el "children"))) "B"))))