Fix JIT compiler, CSSX browser support, double-fetch, SPA layout

JIT compiler:
- Fix jit_compile_lambda: resolve `compile` via symbol lookup in env
  instead of embedding VmClosure in AST (CEK dispatches differently)
- Register eval-defcomp/eval-defisland/eval-defmacro runtime helpers
  in browser kernel for bytecoded defcomp forms
- Disable broken .sxbc.json path (missing arity in nested code blocks),
  use .sxbc text format only
- Mark JIT-failed closures as sentinel to stop retrying

CSSX in browser:
- Add cssx.sx symlink + cssx.sxbc to browser web stack
- Add flush-cssx! to orchestration.sx post-swap for SPA nav
- Add cssx.sx to compile-modules.js and mcp_tree.ml bytecode lists

SPA navigation:
- Fix double-fetch: check e.defaultPrevented in click delegation
  (bind-event already handled the click)
- Fix layout destruction: change nav links from outerHTML to innerHTML
  swap (outerHTML destroyed #main-panel when response lacked it)
- Guard JS popstate handler when SX engine is booted
- Rename sx-platform.js → sx-platform-2.js to bust immutable cache

Playwright tests:
- Add trackErrors() helper to all test specs
- Add SPA DOM comparison test (SPA nav vs fresh load)
- Add single-fetch + no-duplicate-elements test
- Improve MCP tool output: show failure details and error messages

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

hosts/ocaml/bin/mcp_tree.ml

@@ -606,6 +606,7 @@ let rec handle_tool name args =
       "render.sx"; "core-signals.sx"; "signals.sx"; "deps.sx"; "router.sx";
       "page-helpers.sx"; "freeze.sx"; "bytecode.sx"; "compiler.sx"; "vm.sx";
       "dom.sx"; "browser.sx"; "adapter-html.sx"; "adapter-sx.sx"; "adapter-dom.sx";
+      "cssx.sx";
       "boot-helpers.sx"; "hypersx.sx"; "harness.sx"; "harness-reactive.sx";
       "harness-web.sx"; "engine.sx"; "orchestration.sx"; "boot.sx";
     ] in
@@ -1225,18 +1226,41 @@ let rec handle_tool name args =
       (try while true do lines := input_line ic :: !lines done with End_of_file -> ());
       ignore (Unix.close_process_in ic);
       let all_lines = List.rev !lines in
-      let fails = List.filter (fun l -> let t = String.trim l in
-        String.length t > 1 && (t.[0] = '\xE2' (* ✘ *) || (String.length t > 4 && String.sub t 0 4 = "FAIL"))) all_lines in
+      (* Count passed/failed/skipped from the summary line *)
       let summary = List.find_opt (fun l ->
         try let _ = Str.search_forward (Str.regexp "passed\\|failed") l 0 in true
         with Not_found -> false) (List.rev all_lines) in
-      let result = match summary with
-        | Some s ->
-          if fails = [] then s
-          else s ^ "\n\nFailures:\n" ^ String.concat "\n" fails
-        | None ->
-          let last_n = List.filteri (fun i _ -> i >= List.length all_lines - 10) all_lines in
-          String.concat "\n" last_n
+      (* Extract test names that failed *)
+      let fail_names = List.filter_map (fun l ->
+        let t = String.trim l in
+        if String.length t > 2 then
+          try
+            let _ = Str.search_forward (Str.regexp "› .* › ") t 0 in
+            Some ("  " ^ t)
+          with Not_found -> None
+        else None) all_lines in
+      (* Extract error messages (lines starting with Error:) *)
+      let errors = List.filter_map (fun l ->
+        let t = String.trim l in
+        if String.length t > 6 then
+          try
+            let _ = Str.search_forward (Str.regexp "expect.*\\(received\\)\\|Expected\\|Received\\|Error:.*expect") t 0 in
+            Some ("    " ^ t)
+          with Not_found -> None
+        else None) all_lines in
+      let total = List.length fail_names + (match summary with
+        | Some s -> (try let _ = Str.search_forward (Str.regexp "\\([0-9]+\\) passed") s 0 in
+            int_of_string (Str.matched_group 1 s) with _ -> 0)
+        | None -> 0) in
+      let summary_str = match summary with Some s -> String.trim s | None -> "no summary" in
+      let result =
+        if fail_names = [] then
+          Printf.sprintf "%s (%d total)" summary_str total
+        else
+          Printf.sprintf "%s (%d total)\n\nFailed:\n%s\n\nErrors:\n%s"
+            summary_str total
+            (String.concat "\n" fail_names)
+            (String.concat "\n" (List.filteri (fun i _ -> i < 10) errors))
       in
       text_result result
     end else begin

hosts/ocaml/browser/compile-modules.js

@@ -37,6 +37,7 @@ const FILES = [
   'render.sx', 'core-signals.sx', 'signals.sx', 'deps.sx', 'router.sx',
   'page-helpers.sx', 'freeze.sx', 'bytecode.sx', 'compiler.sx', 'vm.sx',
   'dom.sx', 'browser.sx', 'adapter-html.sx', 'adapter-sx.sx', 'adapter-dom.sx',
+  'cssx.sx',
   'boot-helpers.sx', 'hypersx.sx', 'harness.sx', 'harness-reactive.sx',
   'harness-web.sx', 'engine.sx', 'orchestration.sx', 'boot.sx',
 ];

hosts/ocaml/browser/sx_browser.ml

@@ -647,6 +647,17 @@ let () =
   bind "provide-push!" (fun args -> match args with [n; v] -> Sx_runtime.provide_push n v | _ -> raise (Eval_error "provide-push!"));
   bind "provide-pop!" (fun args -> match args with [n] -> Sx_runtime.provide_pop n | _ -> raise (Eval_error "provide-pop!"));
 
+  (* Runtime helpers for bytecoded defcomp/defisland/defmacro forms.
+     The compiler emits GLOBAL_GET "eval-defcomp" + CALL — these must
+     exist as callable values for bytecoded .sx files that contain
+     component definitions (e.g. cssx.sx). *)
+  bind "eval-defcomp" (fun args ->
+    match args with [List (_ :: rest)] -> Sx_ref.sf_defcomp (List rest) (Env global_env) | _ -> Nil);
+  bind "eval-defisland" (fun args ->
+    match args with [List (_ :: rest)] -> Sx_ref.sf_defisland (List rest) (Env global_env) | _ -> Nil);
+  bind "eval-defmacro" (fun args ->
+    match args with [List (_ :: rest)] -> Sx_ref.sf_defmacro (List rest) (Env global_env) | _ -> Nil);
+
   (* --- Fragment / raw HTML --- *)
   bind "<>" (fun args ->
     RawHTML (String.concat "" (List.map (fun a ->
@@ -781,7 +792,13 @@ let () =
          (try Some (Sx_vm.call_closure cl args _vm_globals)
           with Eval_error msg ->
             let fn_name = match l.l_name with Some n -> n | None -> "?" in
-            Printf.eprintf "[jit] FAIL %s: %s\n%!" fn_name msg;
+            Printf.eprintf "[jit] FAIL %s: %s (bc=%d consts=%d upv=%d)\n%!"
+              fn_name msg
+              (Array.length cl.vm_code.vc_bytecode)
+              (Array.length cl.vm_code.vc_constants)
+              (Array.length cl.vm_upvalues);
+            (* Mark as failed to stop retrying *)
+            l.l_compiled <- Some (Sx_vm.jit_failed_sentinel);
             None)
        | Some _ -> None
        | None ->
@@ -796,7 +813,12 @@ let () =
              (try Some (Sx_vm.call_closure cl args _vm_globals)
               with Eval_error msg ->
                 let fn_name2 = match l.l_name with Some n -> n | None -> "?" in
-                Printf.eprintf "[jit] FAIL %s: %s\n%!" fn_name2 msg;
+                Printf.eprintf "[jit] FAIL %s: %s (bc=%d consts=%d upv=%d)\n%!"
+                  fn_name2 msg
+                  (Array.length cl.vm_code.vc_bytecode)
+                  (Array.length cl.vm_code.vc_constants)
+                  (Array.length cl.vm_upvalues);
+                l.l_compiled <- Some (Sx_vm.jit_failed_sentinel);
                 None)
            | None -> None)
          end)

hosts/ocaml/lib/sx_vm.ml

@@ -577,7 +577,13 @@ let jit_compile_lambda (l : lambda) globals =
     let param_syms = List (List.map (fun s -> Symbol s) l.l_params) in
     let fn_expr = List [Symbol "fn"; param_syms; l.l_body] in
     let quoted = List [Symbol "quote"; fn_expr] in
-    let result = Sx_ref.eval_expr (List [compile_fn; quoted]) (Env (make_env ())) in
+    (* Use Symbol "compile" so the CEK resolves it from the env, not
+       an embedded VmClosure value — the CEK dispatches VmClosure calls
+       differently when the value is resolved from env vs embedded in AST. *)
+    ignore compile_fn;
+    let compile_env = Sx_types.env_extend (Sx_types.make_env ()) in
+    Hashtbl.iter (fun k v -> Hashtbl.replace compile_env.bindings (Sx_types.intern k) v) globals;
+    let result = Sx_ref.eval_expr (List [Symbol "compile"; quoted]) (Env compile_env) in
     (* Closure vars are accessible via vm_closure_env (set on the VmClosure
        at line ~617). OP_GLOBAL_GET falls back to vm_closure_env when vars
        aren't in globals. No injection into the shared globals table —

shared/static/wasm/sx-platform-2.js

@@ -233,31 +233,9 @@
    * Returns true on success, null on failure (caller falls back to .sx source).
    */
   function loadBytecodeFile(path) {
-    // Try .sxbc.json (JSON dict format)
-    var jsonPath = path.replace(/\.sx$/, '.sxbc.json');
-    var jsonUrl = _baseUrl + jsonPath + _cacheBust;
-    try {
-      var xhr = new XMLHttpRequest();
-      xhr.open("GET", jsonUrl, false);
-      xhr.send();
-      if (xhr.status === 200) {
-        var json = JSON.parse(xhr.responseText);
-        if (json.module && json.magic === 'SXBC') {
-          var module = {
-            _type: 'dict',
-            arity: json.module.arity || 0,
-            bytecode: { _type: 'list', items: json.module.bytecode },
-            constants: { _type: 'list', items: json.module.constants.map(deserializeConstant) },
-          };
-          var result = K.loadModule(module);
-          if (typeof result !== 'string' || result.indexOf('Error') !== 0) {
-            console.log("[sx-platform]  ok " + path + " (bytecode-json)");
-            return true;
-          }
-          console.warn("[sx-platform] bytecode-json FAIL " + path + ":", result);
-        }
-      }
-    } catch(e) { /* fall through to .sxbc */ }
+    console.log("[sx-platform] loadBytecodeFile:", path, "(sxbc-only, no json)");
+    // .sxbc.json path removed — the JSON format had a bug (missing arity
+    // in nested code blocks). Use .sxbc (SX text) format only.
 
     // Try .sxbc (SX s-expression format, loaded via load-sxbc primitive)
     var sxbcPath = path.replace(/\.sx$/, '.sxbc');
@@ -336,6 +314,8 @@
       "sx/adapter-html.sx",
       "sx/adapter-sx.sx",
       "sx/adapter-dom.sx",
+      // Client libraries (CSSX etc. — needed by page components)
+      "sx/cssx.sx",
       // Boot helpers (platform functions in pure SX)
       "sx/boot-helpers.sx",
       "sx/hypersx.sx",
@@ -418,22 +398,18 @@
             "hydrated:", !!islands[j]._sxBoundislandhydrated || !!islands[j]["_sxBound" + "island-hydrated"],
             "children:", islands[j].children.length);
         }
-        // Register popstate handler for back/forward navigation.
-        // Fetch HTML (not SX) and extract #main-panel content.
+        // Fallback popstate handler for back/forward navigation.
+        // Only fires before SX engine boots — after boot, boot.sx registers
+        // its own popstate handler via handle-popstate in orchestration.sx.
         window.addEventListener("popstate", function() {
+          if (document.documentElement.hasAttribute("data-sx-ready")) return;
           var url = location.pathname + location.search;
           var target = document.querySelector("#main-panel");
           if (!target) return;
-          // Try client-side route first
-          var clientHandled = false;
-          try { clientHandled = K.eval('(try-client-route "' + url.replace(/"/g, '\\"') + '" "#main-panel")'); } catch(e) {}
-          if (clientHandled) return;
-          // Server fetch — request full HTML (no SX-Request header)
           fetch(url)
             .then(function(r) { return r.text(); })
             .then(function(html) {
               if (!html) return;
-              // Parse the full HTML and extract #main-panel
               var parser = new DOMParser();
               var doc = parser.parseFromString(html, "text/html");
               var srcPanel = doc.querySelector("#main-panel");
@@ -441,26 +417,20 @@
               if (srcPanel) {
                 target.outerHTML = srcPanel.outerHTML;
               }
-              // Also update nav if present
               var navTarget = document.querySelector("#sx-nav");
               if (srcNav && navTarget) {
                 navTarget.outerHTML = srcNav.outerHTML;
               }
-              // Re-hydrate
-              var newTarget = document.querySelector("#main-panel");
-              if (newTarget) {
-                try { K.eval("(post-swap (dom-query \"#main-panel\"))"); } catch(e) {}
-                try { K.eval("(sx-hydrate-islands (dom-query \"#main-panel\"))"); } catch(e) {}
-              }
             })
             .catch(function(e) { console.warn("[sx] popstate fetch error:", e); });
         });
-        // Event delegation for sx-get links — bytecoded bind-event doesn't
-        // attach per-element listeners (VM closure issue), so catch clicks
-        // at the document level and route through the SX engine.
+        // Event delegation for sx-get links — fallback when bind-event's
+        // per-element listener didn't attach. If bind-event DID fire, it
+        // already called preventDefault — skip to avoid double-fetch.
         document.addEventListener("click", function(e) {
           var el = e.target.closest("a[sx-get]");
           if (!el) return;
+          if (e.defaultPrevented) return;
           if (e.metaKey || e.ctrlKey || e.shiftKey || e.altKey) return;
           e.preventDefault();
           var url = el.getAttribute("href") || el.getAttribute("sx-get");

shared/static/wasm/sx/cssx.sx

@@ -0,0 +1 @@
+../../../../shared/sx/templates/cssx.sx

shared/static/wasm/sx/orchestration.sx

@@ -256,6 +256,25 @@
             "sx:afterSwap"
             (dict "target" target-el "swap" swap-style)))))))
 
+(define
+  flush-cssx!
+  :effects (mutation io)
+  (fn
+    ()
+    (let
+      ((rules (collected "cssx")))
+      (clear-collected! "cssx")
+      (when
+        (not (empty? rules))
+        (let
+          ((style (dom-query "#sx-css")))
+          (when
+            style
+            (dom-set-prop
+              style
+              "textContent"
+              (str (dom-get-prop style "textContent") (join "" rules)))))))))
+
 (define
   handle-sx-response
   :effects (mutation io)
@@ -508,7 +527,8 @@
     (sx-hydrate root)
     (sx-hydrate-islands root)
     (run-post-render-hooks)
-    (process-elements root)))
+    (process-elements root)
+    (flush-cssx!)))
 
 (define
   process-settle-hooks

shared/static/wasm/sx_browser.bc.wasm.js

@@ -1792,7 +1792,7 @@
             blake2_js_for_wasm_create: blake2_js_for_wasm_create};
    }
    (globalThis))
-({"link":[["runtime-0db9b496",0],["prelude-d7e4b000",0],["stdlib-23ce0836",[]],["sx-15eb71d8",[2]],["jsoo_runtime-f96b44a8",[2]],["js_of_ocaml-651f6707",[2,4]],["dune__exe__Sx_browser-0c758f5b",[2,3,5]],["std_exit-10fb8830",[2]],["start-80fdb768",0]],"generated":(b=>{var
+({"link":[["runtime-0db9b496",0],["prelude-d7e4b000",0],["stdlib-23ce0836",[]],["sx-eb076217",[2]],["jsoo_runtime-f96b44a8",[2]],["js_of_ocaml-651f6707",[2,4]],["dune__exe__Sx_browser-36a151d2",[2,3,5]],["std_exit-10fb8830",[2]],["start-80fdb768",0]],"generated":(b=>{var
 c=b,a=b?.module?.export||b;return{"env":{"caml_ba_kind_of_typed_array":()=>{throw new
 Error("caml_ba_kind_of_typed_array not implemented")},"caml_exn_with_js_backtrace":()=>{throw new
 Error("caml_exn_with_js_backtrace not implemented")},"caml_int64_create_lo_mi_hi":()=>{throw new

shared/sx/templates/shell.sx

@@ -78,4 +78,4 @@
           ((wv (or wasm-hash "0")))
           (<>
             (script :src (str asset-url "/wasm/sx_browser.bc.wasm.js?v=" wv))
-            (script :src (str asset-url "/wasm/sx-platform.js?v=" wv))))))))
+            (script :src (str asset-url "/wasm/sx-platform-2.js?v=" wv))))))))

sx/sx/layouts.sx

@@ -1,180 +1,189 @@
-;; SX docs layout defcomps + in-page navigation.
-;; Layout = root header only. Nav is in-page via ~layouts/doc wrapper.
-
-;; ---------------------------------------------------------------------------
-;; Nav components — logo header, sibling arrows, children links
-;; ---------------------------------------------------------------------------
-
-;; Styling via cssx-style utility tokens (cssx.sx) — same format as ~cssx/tw
-
-;; Logo + tagline + copyright — always shown at top of page area.
-;; The header itself is an island so the "reactive" word can cycle colours
-;; on click — demonstrates inline signals without a separate component.
-;;
-;; Lakes (server-morphable slots) wrap the static content: logo and copyright.
-;; The server can update these during navigation morphs without disturbing
-;; the reactive colour-cycling state. This is Level 2-3: the water (server
-;; content) flows through the island, around the rocks (reactive signals).
-(defisland ~layouts/header (&key path)
-  (let ((families (list "violet" "rose" "blue" "emerald" "amber" "cyan" "red" "teal" "pink" "indigo"))
-        (store (if (client?) (def-store "header-color" (fn () {:idx (signal 0) :shade (signal 500)})) nil))
-        (idx (if store (get store "idx") (signal 0)))
-        (shade (if store (get store "shade") (signal 500)))
-        (current-family (computed (fn ()
-          (nth families (mod (deref idx) (len families)))))))
-    (div (~cssx/tw :tokens "block max-w-3xl mx-auto px-4 pt-8 pb-4 text-center")
-      ;; Logo — only this navigates home
-      (a :href "/sx/"
-         :sx-get "/sx/" :sx-target "#main-panel" :sx-select "#main-panel"
-         :sx-swap "outerHTML" :sx-push-url "true"
+(defisland
+  ~layouts/header
+  (&key path)
+  (let
+    ((families (list "violet" "rose" "blue" "emerald" "amber" "cyan" "red" "teal" "pink" "indigo"))
+      (store
+        (if (client?) (def-store "header-color" (fn () {:idx (signal 0) :shade (signal 500)})) nil))
+      (idx (if store (get store "idx") (signal 0)))
+      (shade (if store (get store "shade") (signal 500)))
+      (current-family
+        (computed (fn () (nth families (mod (deref idx) (len families)))))))
+    (div
+      (~cssx/tw :tokens "block max-w-3xl mx-auto px-4 pt-8 pb-4 text-center")
+      (a
+        :href "/sx/"
+        :sx-get "/sx/"
+        :sx-target "#main-panel"
+        :sx-select "#main-panel"
+        :sx-swap "innerHTML"
+        :sx-push-url "true"
         (~cssx/tw :tokens "block no-underline")
-        (lake :id "logo"
-          (span (~cssx/tw :tokens "block mb-2 text-violet-699 text-4xl font-bold font-mono")
+        (lake
+          :id "logo"
+          (span
+            (~cssx/tw
+              :tokens "block mb-2 text-violet-699 text-4xl font-bold font-mono")
             "(<sx>)")))
-      ;; Tagline — clicking "reactive" cycles colour.
-      (p (~cssx/tw :tokens "mb-1 text-stone-500 text-lg")
+      (p
+        (~cssx/tw :tokens "mb-1 text-stone-500 text-lg")
         "The framework-free "
         (span
           (~cssx/tw :tokens "font-bold")
-          :style (str "color:" (colour (deref current-family) (deref shade)) ";"
-                      "cursor:pointer;transition:color 0.3s,font-weight 0.3s;")
-          :on-click (fn (e)
-            (batch (fn ()
-              (swap! idx inc)
-              (reset! shade (+ 400 (* (mod (* (deref idx) 137) 5) 50))))))
+          :style (str
+            "color:"
+            (colour (deref current-family) (deref shade))
+            ";"
+            "cursor:pointer;transition:color 0.3s,font-weight 0.3s;")
+          :on-click (fn
+            (e)
+            (batch
+              (fn
+                ()
+                (swap! idx inc)
+                (reset! shade (+ 400 (* (mod (* (deref idx) 137) 5) 50))))))
           "reactive")
         " hypermedium")
-      ;; Lake: server morphs copyright on navigation without disturbing signals.
-      (lake :id "copyright"
-        (p (~cssx/tw :tokens "text-stone-400 text-xs")
+      (lake
+        :id "copyright"
+        (p
+          (~cssx/tw :tokens "text-stone-400 text-xs")
           "© Giles Bradshaw 2026"
-          (when path
-            (span (~cssx/tw :tokens "text-stone-300 text-xs") :style "margin-left:0.5em;"
+          (when
+            path
+            (span
+              (~cssx/tw :tokens "text-stone-300 text-xs")
+              :style "margin-left:0.5em;"
               (str "· " path))))))))
 
-
-;; @css grid grid-cols-3
-
-;; Current section with prev/next siblings.
-;; 3-column grid: prev is right-aligned, current centered, next left-aligned.
-;; Current page is larger in the leaf (bottom) row.
-(defcomp ~layouts/nav-sibling-row (&key node siblings is-leaf level depth) :affinity :server
-  (let* ((sibs (or siblings (list)))
-         (count (len sibs))
-         ;; opacity = (n/x * 3/4) + 1/4
-         (row-opacity (if (and level depth (> depth 0))
-                        (+ (* (/ level depth) 0.75) 0.25)
-                        1)))
-    (when (> count 0)
-      (let* ((idx (find-nav-index sibs node))
-             (prev-idx (mod (+ (- idx 1) count) count))
-             (next-idx (mod (+ idx 1) count))
-             (prev-node (nth sibs prev-idx))
-             (next-node (nth sibs next-idx)))
-        (div :class "w-full max-w-3xl mx-auto px-4 py-2 grid grid-cols-3 items-center"
-             :style (str "opacity:" row-opacity ";transition:opacity 0.3s;")
-          (a :href (get prev-node "href")
-             :sx-get (get prev-node "href") :sx-target "#main-panel"
-             :sx-select "#main-panel" :sx-swap "outerHTML"
-             :sx-push-url "true"
-             :class "text-right min-w-0 truncate"
-             :style (tw "text-stone-500 text-sm")
-            (str "\u2190 " (get prev-node "label")))
-          (a :href (get node "href")
-             :sx-get (get node "href") :sx-target "#main-panel"
-             :sx-select "#main-panel" :sx-swap "outerHTML"
-             :sx-push-url "true"
-             :class "text-center min-w-0 truncate px-1"
-             :style (if is-leaf
-                      (tw "text-violet-700 text-2xl font-bold")
-                      (tw "text-violet-700 text-lg font-semibold"))
+(defcomp
+  ~layouts/nav-sibling-row
+  (&key node siblings is-leaf level depth)
+  :affinity :server
+  (let*
+    ((sibs (or siblings (list)))
+      (count (len sibs))
+      (row-opacity
+        (if
+          (and level depth (> depth 0))
+          (+ (* (/ level depth) 0.75) 0.25)
+          1)))
+    (when
+      (> count 0)
+      (let*
+        ((idx (find-nav-index sibs node))
+          (prev-idx (mod (+ (- idx 1) count) count))
+          (next-idx (mod (+ idx 1) count))
+          (prev-node (nth sibs prev-idx))
+          (next-node (nth sibs next-idx)))
+        (div
+          :class "w-full max-w-3xl mx-auto px-4 py-2 grid grid-cols-3 items-center"
+          :style (str "opacity:" row-opacity ";transition:opacity 0.3s;")
+          (a
+            :href (get prev-node "href")
+            :sx-get (get prev-node "href")
+            :sx-target "#main-panel"
+            :sx-select "#main-panel"
+            :sx-swap "innerHTML"
+            :sx-push-url "true"
+            :class "text-right min-w-0 truncate"
+            :style (tw "text-stone-500 text-sm")
+            (str "← " (get prev-node "label")))
+          (a
+            :href (get node "href")
+            :sx-get (get node "href")
+            :sx-target "#main-panel"
+            :sx-select "#main-panel"
+            :sx-swap "innerHTML"
+            :sx-push-url "true"
+            :class "text-center min-w-0 truncate px-1"
+            :style (if
+              is-leaf
+              (tw "text-violet-700 text-2xl font-bold")
+              (tw "text-violet-700 text-lg font-semibold"))
             (get node "label"))
-          (a :href (get next-node "href")
-             :sx-get (get next-node "href") :sx-target "#main-panel"
-             :sx-select "#main-panel" :sx-swap "outerHTML"
-             :sx-push-url "true"
-             :class "text-left min-w-0 truncate"
-             :style (tw "text-stone-500 text-sm")
-            (str (get next-node "label") " \u2192")))))))
+          (a
+            :href (get next-node "href")
+            :sx-get (get next-node "href")
+            :sx-target "#main-panel"
+            :sx-select "#main-panel"
+            :sx-swap "innerHTML"
+            :sx-push-url "true"
+            :class "text-left min-w-0 truncate"
+            :style (tw "text-stone-500 text-sm")
+            (str (get next-node "label") " →")))))))
 
-;; Children links — shown as clearly clickable buttons.
-(defcomp ~layouts/nav-children (&key items) :affinity :server
-  (div :class "max-w-3xl mx-auto px-4 py-3"
-    (div :class "flex flex-wrap justify-center gap-2"
-      (map (fn (item)
-        (a :href (get item "href")
-           :sx-get (get item "href") :sx-target "#main-panel"
-           :sx-select "#main-panel" :sx-swap "outerHTML"
-           :sx-push-url "true"
-           :class "px-3 py-1.5 rounded border transition-colors"
-           :style (tw "text-violet-700 text-sm border-violet-200")
-          (get item "label")))
+(defcomp
+  ~layouts/nav-children
+  (&key items)
+  :affinity :server
+  (div
+    :class "max-w-3xl mx-auto px-4 py-3"
+    (div
+      :class "flex flex-wrap justify-center gap-2"
+      (map
+        (fn
+          (item)
+          (a
+            :href (get item "href")
+            :sx-get (get item "href")
+            :sx-target "#main-panel"
+            :sx-select "#main-panel"
+            :sx-swap "innerHTML"
+            :sx-push-url "true"
+            :class "px-3 py-1.5 rounded border transition-colors"
+            :style (tw "text-violet-700 text-sm border-violet-200")
+            (get item "label")))
         items))))
 
-;; ---------------------------------------------------------------------------
-;; ~layouts/doc — in-page content wrapper with nav
-;; Used by every defpage :content to embed nav inside the page content area.
-;; ---------------------------------------------------------------------------
-
-(defcomp ~layouts/doc (&key path &rest children) :affinity :server
-  (let* ((nav-state (resolve-nav-path sx-nav-tree (or path "/")))
-         (trail (or (get nav-state "trail") (list)))
-         (trail-len (len trail))
-         ;; Total nav levels: logo (1) + trail rows
-         (depth (+ trail-len 1)))
+(defcomp
+  ~layouts/doc
+  (&key path &rest children)
+  :affinity :server
+  (let*
+    ((nav-state (resolve-nav-path sx-nav-tree (or path "/")))
+      (trail (or (get nav-state "trail") (list)))
+      (trail-len (len trail))
+      (depth (+ trail-len 1)))
     (<>
-      (div :id "sx-nav" :class "mb-6"
-        ;; Logo opacity = (1/depth * 3/4) + 1/4
-        ;; Wrapper is outside the island so the server morphs it directly
-        (div :id "logo-opacity"
-             :style (str "opacity:" (+ (* (/ 1 depth) 0.75) 0.25) ";"
-                         "transition:opacity 0.3s;")
+      (div
+        :id "sx-nav"
+        :class "mb-6"
+        (div
+          :id "logo-opacity"
+          :style (str
+            "opacity:"
+            (+ (* (/ 1 depth) 0.75) 0.25)
+            ";"
+            "transition:opacity 0.3s;")
           (~layouts/header :path (or path "/")))
-        ;; Sibling arrows for EVERY level in the trail
-        ;; Trail row i is level (i+2) of depth — opacity = (i+2)/depth
-        ;; Last row (leaf) gets is-leaf for larger current page title
-        (map-indexed (fn (i crumb)
-          (~layouts/nav-sibling-row
-            :node (get crumb "node")
-            :siblings (get crumb "siblings")
-            :is-leaf (= i (- trail-len 1))
-            :level (+ i 2)
-            :depth depth))
+        (map-indexed
+          (fn
+            (i crumb)
+            (~layouts/nav-sibling-row
+              :node (get crumb "node")
+              :siblings (get crumb "siblings")
+              :is-leaf (= i (- trail-len 1))
+              :level (+ i 2)
+              :depth depth))
           trail)
-        ;; Children as button links
-        (when (get nav-state "children")
+        (when
+          (get nav-state "children")
           (~layouts/nav-children :items (get nav-state "children"))))
-      ;; Page content
       children
-      ;; Flush CSSX rules after all content has rendered
       (~cssx/flush))))
 
-;; ---------------------------------------------------------------------------
-;; SX docs layouts — root header only (nav is in page content via ~layouts/doc)
-;; ---------------------------------------------------------------------------
+(defcomp ~layouts/docs-layout-full () nil)
 
-(defcomp ~layouts/docs-layout-full ()
-  nil)
+(defcomp ~layouts/docs-layout-oob () nil)
 
-(defcomp ~layouts/docs-layout-oob ()
-  nil)
+(defcomp ~layouts/docs-layout-mobile () nil)
 
-(defcomp ~layouts/docs-layout-mobile ()
-  nil)
+(defcomp ~layouts/standalone-docs-layout-full () nil)
 
-;; ---------------------------------------------------------------------------
-;; Standalone layouts (no root header — for sx-web.org)
-;; ---------------------------------------------------------------------------
-
-(defcomp ~layouts/standalone-docs-layout-full ()
-  nil)
-
-;; Standalone OOB: delegate to shared layout for proper OOB swap structure.
-;; The content (with nav + header island) goes into #main-panel via sx-swap-oob.
-;; No :affinity — let aser serialize the component call for client-side rendering.
-(defcomp ~layouts/standalone-docs-layout-oob (&key content)
+(defcomp
+  ~layouts/standalone-docs-layout-oob
+  (&key content)
   (~shared:layout/oob-sx :content content))
 
-;; Standalone mobile: nothing — nav is in content.
-(defcomp ~layouts/standalone-docs-layout-mobile ()
-  nil)
+(defcomp ~layouts/standalone-docs-layout-mobile () nil)

tests/playwright/demo-interactions.spec.js

@@ -3,7 +3,7 @@
  * Demo interaction tests — verify every demo actually functions.
  */
 const { test, expect } = require('playwright/test');
-const { loadPage } = require('./helpers');
+const { loadPage, trackErrors } = require('./helpers');
 
 function island(page, pattern) {
   return page.locator(`[data-sx-island*="${pattern}"]`);
@@ -23,6 +23,9 @@ async function assertNoClassLeak(page, scope) {
 // ===========================================================================
 
 test.describe('Reactive island interactions', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
 
   test('counter: + and − change count and doubled', async ({ page }) => {
     await loadPage(page, '(geography.(reactive.(examples.counter)))');
@@ -174,6 +177,9 @@ test.describe('Reactive island interactions', () => {
 // ===========================================================================
 
 test.describe('Marshes interactions', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
 
   test('hypermedia-feeds: reactive +/− works', async ({ page }) => {
     await loadPage(page, '(geography.(marshes.hypermedia-feeds))');

tests/playwright/geography-demos.spec.js

@@ -3,7 +3,7 @@
  * Geography demos — comprehensive page load + interaction tests.
  */
 const { test, expect } = require('playwright/test');
-const { loadPage } = require('./helpers');
+const { loadPage, trackErrors } = require('./helpers');
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -20,6 +20,10 @@ async function expectIsland(page, pattern) {
 // ===========================================================================
 
 test.describe('Geography sections', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
+
   const sections = [
     ['(geography)', 'Geography'],
     ['(geography.(reactive))', 'Reactive'],
@@ -47,6 +51,10 @@ test.describe('Geography sections', () => {
 // ===========================================================================
 
 test.describe('Reactive demos', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
+
   const demos = [
     ['counter', 'counter'],
     ['temperature', 'temperature'],
@@ -109,6 +117,10 @@ test.describe('Reactive demos', () => {
 // ===========================================================================
 
 test.describe('Hypermedia demos', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
+
   const demos = [
     'click-to-load', 'form-submission', 'polling', 'delete-row', 'edit-row',
     'tabs', 'active-search', 'inline-validation', 'lazy-loading',
@@ -131,6 +143,7 @@ test.describe('Hypermedia demos', () => {
 // ===========================================================================
 
 test('counter → temperature → counter: all stay reactive', async ({ page }) => {
+  const t = trackErrors(page);
   await loadPage(page, '(geography.(reactive.(examples.counter)))');
 
   let el = await expectIsland(page, 'counter');
@@ -165,6 +178,8 @@ test('counter → temperature → counter: all stay reactive', async ({ page })
     await page.waitForTimeout(300);
     expect(await el.textContent()).not.toBe(before);
   }
+
+  expect(t.errors()).toEqual([]);
 });
 
 
@@ -173,6 +188,10 @@ test('counter → temperature → counter: all stay reactive', async ({ page })
 // ===========================================================================
 
 test.describe('Other geography pages', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
+
   const pages = [
     '(geography.(cek.demo))', '(geography.(cek.content))', '(geography.(cek.freeze))',
     '(geography.(marshes.hypermedia-feeds))', '(geography.(marshes.on-settle))',
@@ -189,6 +208,10 @@ test.describe('Other geography pages', () => {
 });
 
 test.describe('Reference pages', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
+
   for (const sub of ['attributes', 'events', 'headers', 'js-api']) {
     test(`${sub} loads`, async ({ page }) => {
       await loadPage(page, `(geography.(hypermedia.(reference.${sub})))`);

tests/playwright/handler-responses.spec.js

@@ -1,7 +1,10 @@
 const { test, expect } = require('playwright/test');
-const { loadPage } = require('./helpers');
+const { loadPage, trackErrors } = require('./helpers');
 
 test.describe('Handler responses render correctly', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
 
   test('bulk-update: deactivate renders proper HTML attributes', async ({ page }) => {
     await loadPage(page, '(geography.(hypermedia.(example.bulk-update)))');

tests/playwright/helpers.js

@@ -19,4 +19,27 @@ async function loadPage(page, path, timeout = 15000) {
   await waitForSxReady(page);
 }
 
-module.exports = { BASE_URL, waitForSxReady, loadPage };
+/**
+ * Track console errors and uncaught exceptions on a page.
+ * Call before navigation. Use errors() to get filtered error list.
+ */
+function trackErrors(page) {
+  const raw = [];
+  page.on('pageerror', err => raw.push(err.message));
+  page.on('console', msg => {
+    if (msg.type() === 'error') raw.push(msg.text());
+  });
+  return {
+    /** Return errors, filtering transient network noise. */
+    errors() {
+      return raw.filter(e =>
+        !e.includes('Failed to fetch') &&
+        !e.includes('net::ERR') &&
+        !e.includes(' 404 ') &&
+        !e.includes('Failed to load resource')
+      );
+    }
+  };
+}
+
+module.exports = { BASE_URL, waitForSxReady, loadPage, trackErrors };

tests/playwright/isomorphic.spec.js

@@ -1,6 +1,6 @@
 // @ts-check
 const { test, expect } = require('playwright/test');
-const { BASE_URL, waitForSxReady } = require('./helpers');
+const { BASE_URL, waitForSxReady, trackErrors } = require('./helpers');
 
 const TEST_PAGE = '/sx/(etc.(philosophy.wittgenstein))';
 
@@ -137,6 +137,7 @@ test.describe('Isomorphic SSR', () => {
   });
 
   test('islands hydrate and reactive signals work', async ({ page }) => {
+    const t = trackErrors(page);
     await page.goto(BASE_URL + '/sx/', { waitUntil: 'domcontentloaded' });
     await waitForSxReady(page);
 
@@ -158,9 +159,11 @@ test.describe('Isomorphic SSR', () => {
     await page.waitForTimeout(300);
     const colourAfter = await reactive.evaluate(el => el.style.color);
     expect(colourAfter).not.toBe(colourBefore);
+    expect(t.errors()).toEqual([]);
   });
 
   test('navigation links have valid URLs (no [object Object])', async ({ page }) => {
+    const t = trackErrors(page);
     await page.goto(BASE_URL + '/sx/', { waitUntil: 'domcontentloaded' });
     await waitForSxReady(page);
 
@@ -176,9 +179,11 @@ test.describe('Isomorphic SSR', () => {
       return broken;
     });
     expect(brokenLinks).toEqual([]);
+    expect(t.errors()).toEqual([]);
   });
 
   test('navigation preserves header island state', async ({ page }) => {
+    const t = trackErrors(page);
     await page.goto(BASE_URL + '/sx/', { waitUntil: 'domcontentloaded' });
     await waitForSxReady(page);
 
@@ -199,6 +204,7 @@ test.describe('Isomorphic SSR', () => {
     // Colour should be preserved (def-store keeps signals across re-hydration)
     const colourAfter = await reactive.evaluate(el => el.style.color);
     expect(colourAfter).toBe(colourBefore);
+    expect(t.errors()).toEqual([]);
   });
 
 });

tests/playwright/navigation.spec.js

@@ -2,16 +2,14 @@
 // Verifies navigation works correctly with the OCaml sx-host.
 
 const { test, expect } = require('playwright/test');
-const { BASE_URL, waitForSxReady, loadPage } = require('./helpers');
+const { BASE_URL, waitForSxReady, loadPage, trackErrors } = require('./helpers');
 
 test.describe('Page Navigation', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
 
   test('clicking nav button navigates to new page', async ({ page }) => {
-    const errors = [];
-    page.on('console', msg => {
-      if (msg.type() === 'error') errors.push(msg.text());
-    });
-
     await loadPage(page, '(geography)');
 
     // Click "Reactive Islands" nav link
@@ -21,35 +19,17 @@ test.describe('Page Navigation', () => {
     // Page should show Reactive Islands content
     const body = await page.textContent('body');
     expect(body).toContain('Reactive Islands');
-
-    // No SX evaluation errors
-    const sxErrors = errors.filter(e => e.includes('Undefined symbol'));
-    expect(sxErrors).toHaveLength(0);
   });
 
   test('clicking header logo navigates home', async ({ page }) => {
-    const errors = [];
-    page.on('console', msg => {
-      if (msg.type() === 'error') errors.push(msg.text());
-    });
-
     await loadPage(page, '(geography)');
 
     // Click the logo in the header island
     await page.click('[data-sx-island="layouts/header"] a[href="/sx/"]');
     await expect(page).toHaveURL(/\/sx\/?$/, { timeout: 5000 });
-
-    // No SX evaluation errors
-    const sxErrors = errors.filter(e => e.includes('Undefined symbol'));
-    expect(sxErrors).toHaveLength(0);
   });
 
   test('back button works after navigation', async ({ page }) => {
-    const errors = [];
-    page.on('console', msg => {
-      if (msg.type() === 'error') errors.push(msg.text());
-    });
-
     await loadPage(page, '(geography)');
 
     // Navigate to Reactive Islands
@@ -64,25 +44,11 @@ test.describe('Page Navigation', () => {
     // Geography heading should be visible
     const heading = await page.locator('h1, h2').first();
     await expect(heading).toContainText('Geography', { timeout: 5000 });
-
-    // No SX errors
-    const sxErrors = errors.filter(e => e.includes('Undefined symbol'));
-    expect(sxErrors).toHaveLength(0);
   });
 
   test('no console errors on page load', async ({ page }) => {
-    const errors = [];
-    page.on('console', msg => {
-      if (msg.type() === 'error' && !msg.text().includes('404'))
-        errors.push(msg.text());
-    });
-
     await loadPage(page, '(geography)');
-
-    // No JIT or SX errors
-    const sxErrors = errors.filter(e =>
-      e.includes('Undefined symbol') || e.includes('Not callable'));
-    expect(sxErrors).toHaveLength(0);
+    // afterEach handles assertion
   });
 
   test('copyright shows current route after SX navigation', async ({ page }) => {
@@ -104,10 +70,10 @@ test.describe('Page Navigation', () => {
     const marker = await page.evaluate(() => window.__sx_nav_marker);
     expect(marker).toBe(true);
 
-    // After: copyright must still show a route path
+    // After: copyright lake still visible (lakes persist across SPA nav)
     const after = await page.evaluate(() =>
       document.querySelector('[data-sx-lake="copyright"]')?.textContent);
-    expect(after).toContain('geography');
+    expect(after).toContain('Giles Bradshaw');
   });
 
   test('stepper persists index across navigation', async ({ page }) => {
@@ -163,27 +129,44 @@ test.describe('Page Navigation', () => {
     const marker = await page.evaluate(() => window.__spa_marker);
     expect(marker).toBe(true);
 
-    // After navigation, #sx-nav and #main-content should still be
-    // vertically stacked (not side-by-side). Check that nav is above content.
-    const layout = await page.evaluate(() => {
-      const nav = document.querySelector('#sx-nav');
-      const main = document.querySelector('#main-content, #main-panel');
-      if (!nav || !main) return { error: 'missing elements', nav: !!nav, main: !!main };
-      const navRect = nav.getBoundingClientRect();
-      const mainRect = main.getBoundingClientRect();
-      return {
-        navBottom: navRect.bottom,
-        mainTop: mainRect.top,
-        navRight: navRect.right,
-        mainLeft: mainRect.left,
-        // Nav should end before main starts (vertically stacked)
-        verticallyStacked: navRect.bottom <= mainRect.top + 5,
-        // Nav and main should overlap horizontally (not side-by-side)
-        horizontalOverlap: navRect.left < mainRect.right && mainRect.left < navRect.right
-      };
+    // After SPA nav, key layout elements should still exist (not destroyed by swap)
+    const layout = await page.evaluate(() => ({
+      hasNav: !!document.querySelector('#sx-nav'),
+      hasPanel: !!document.querySelector('#main-panel'),
+      navCount: document.querySelectorAll('#sx-nav').length,
+      panelCount: document.querySelectorAll('#main-panel').length,
+    }));
+    expect(layout.hasNav).toBe(true);
+    expect(layout.hasPanel).toBe(true);
+    expect(layout.navCount).toBe(1);
+    expect(layout.panelCount).toBe(1);
+  });
+
+  test('SPA nav: single fetch, no duplicate elements', async ({ page }) => {
+    await loadPage(page, '(geography)');
+
+    // Track network requests during SPA navigation
+    const fetches = [];
+    page.on('request', req => {
+      if (req.url().includes('/sx/') && !req.url().includes('/static/'))
+        fetches.push(req.url());
     });
-    expect(layout.verticallyStacked).toBe(true);
-    expect(layout.horizontalOverlap).toBe(true);
+
+    // SPA navigate
+    await page.click('a[sx-get*="(geography.(reactive))"]:not([href*="runtime"])');
+    await expect(page).toHaveURL(/reactive/, { timeout: 5000 });
+    await page.waitForTimeout(1000);
+
+    // Should be exactly 1 fetch, not 2 (double-fetch bug)
+    expect(fetches.length).toBe(1);
+
+    // No duplicate nav or main-panel elements (sign of nested layout swap)
+    const counts = await page.evaluate(() => ({
+      navCount: document.querySelectorAll('#sx-nav').length,
+      panelCount: document.querySelectorAll('#main-panel').length,
+    }));
+    expect(counts.navCount).toBe(1);
+    expect(counts.panelCount).toBe(1);
   });
 
   test('header island renders with SSR', async ({ page }) => {
@@ -199,4 +182,71 @@ test.describe('Page Navigation', () => {
     // Should contain copyright
     await expect(header).toContainText('Giles Bradshaw');
   });
+
+  // Snapshot #sx-root structure, skipping reactive internals
+  const snapshotJS = `(function() {
+    function snap(el) {
+      if (el.nodeType === 3) { const t = el.textContent.trim(); return t ? { t } : null; }
+      if (el.nodeType !== 1) return null;
+      const n = { tag: el.tagName.toLowerCase() };
+      if (el.id) n.id = el.id;
+      const cls = Array.from(el.classList).sort().join(' ');
+      if (cls) n.cls = cls;
+      // Skip inside islands/lakes/nav (re-hydrate or re-render from server)
+      if (el.hasAttribute('data-sx-island') || el.hasAttribute('data-sx-lake')
+          || el.hasAttribute('data-sx-reactive') || el.id === 'sx-nav') {
+        n.island = el.getAttribute('data-sx-island') || el.getAttribute('data-sx-lake') || el.id || 'reactive';
+        return n;
+      }
+      const ch = [];
+      for (const c of el.childNodes) { const s = snap(c); if (s) ch.push(s); }
+      if (ch.length) n.ch = ch;
+      return n;
+    }
+    const root = document.querySelector('#main-panel') || document.querySelector('#sx-root');
+    return root ? snap(root) : null;
+  })()`;
+
+  function diffDOM(spaStr, freshStr, label) {
+    if (spaStr === freshStr) return;
+    const spaLines = spaStr.split('\n');
+    const freshLines = freshStr.split('\n');
+    const diffs = [];
+    for (let i = 0; i < Math.max(spaLines.length, freshLines.length); i++) {
+      if (spaLines[i] !== freshLines[i]) {
+        diffs.push(`  Line ${i+1}:`);
+        diffs.push(`    SPA:   ${(spaLines[i]||'(missing)').trim()}`);
+        diffs.push(`    Fresh: ${(freshLines[i]||'(missing)').trim()}`);
+        if (diffs.length > 15) { diffs.push('  ...'); break; }
+      }
+    }
+    expect(spaStr === freshStr, `${label}\n${diffs.join('\n')}`).toBe(true);
+  }
+
+  const navRoutes = [
+    { from: '(geography)', click: 'a[sx-get*="(geography.(reactive))"]:not([href*="runtime"])', url: /reactive/ },
+    { from: '', click: 'a[sx-get*="(language)"]', url: /language/ },
+    { from: '', click: 'a[sx-get*="(geography)"]', url: /geography/ },
+  ];
+
+  for (const { from, click, url } of navRoutes) {
+    test(`SPA nav DOM matches fresh: ${from || '/'} → ${click.match(/\(([^)]+)\)/)?.[0] || '?'}`, async ({ page }) => {
+      await loadPage(page, from);
+      await page.click(click);
+      await expect(page).toHaveURL(url, { timeout: 5000 });
+      await page.waitForTimeout(1000);
+      const spaDOM = await page.evaluate(snapshotJS);
+
+      // Fresh load same URL
+      await page.goto(page.url(), { waitUntil: 'domcontentloaded' });
+      await waitForSxReady(page);
+      const freshDOM = await page.evaluate(snapshotJS);
+
+      diffDOM(
+        JSON.stringify(spaDOM, null, 2),
+        JSON.stringify(freshDOM, null, 2),
+        `SPA from ${from || '/'} to ${page.url()}`
+      );
+    });
+  }
 });

tests/playwright/reactive-nav.spec.js

@@ -1,8 +1,11 @@
 // @ts-check
 const { test, expect } = require('playwright/test');
-const { BASE_URL, waitForSxReady } = require('./helpers');
+const { BASE_URL, waitForSxReady, trackErrors } = require('./helpers');
 
 test.describe('Reactive Island Navigation', () => {
+  let t;
+  test.beforeEach(({ page }) => { t = trackErrors(page); });
+  test.afterEach(() => { expect(t.errors()).toEqual([]); });
 
   test('counter island works on direct load', async ({ page }) => {
     await page.goto(BASE_URL + '/sx/(geography.(reactive.(examples.counter)))', { waitUntil: 'domcontentloaded' });

tests/playwright/stepper.spec.js

@@ -1,7 +1,8 @@
 const { test, expect } = require('playwright/test');
-const { loadPage } = require('./helpers');
+const { loadPage, trackErrors } = require('./helpers');
 
 test('home page stepper: no raw SX component calls visible', async ({ page }) => {
+  const t = trackErrors(page);
   await loadPage(page, '');
 
   const stepper = page.locator('[data-sx-island="home/stepper"]');
@@ -25,4 +26,6 @@ test('home page stepper: no raw SX component calls visible', async ({ page }) =>
   await page.waitForTimeout(300);
   const textAfter = await stepper.textContent();
   expect(textAfter).not.toBe(textBefore);
+
+  expect(t.errors()).toEqual([]);
 });