Fix navigation: deep URL routing, back button, render timeout

- request-handler.sx: replace all dots (not just `.(`) and auto-quote
  undefined symbols as strings so 3-level URLs like
  /sx/(geography.(reactive.(examples.counter))) resolve correctly
- sx-platform.js: register popstate handler (was missing from manual
  boot sequence) and fetch full HTML for back/forward navigation
- sx_ref.ml: add CEK step limit (10M steps) checked every 4096 steps
  so runaway renders return 500 instead of blocking the worker forever
- Rename test-runner.sx → runner-placeholder.sx to avoid `test-` skip
- Playwright config: pin testDir, single worker, ignore worktrees

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

web/request-handler.sx

@@ -1,16 +1,3 @@
-(define
-  sx-url-to-expr
-  (fn
-    (path)
-    (cond
-      (or (= path "/") (= path "/sx/") (= path "/sx"))
-      "home"
-      (starts-with? path "/sx/")
-      (join " " (split (slice path 4 (len path)) "."))
-      (starts-with? path "/")
-      (join " " (split (slice path 1 (len path)) "."))
-      :else path)))
-
 (define
   sx-auto-quote
   (fn
@@ -23,22 +10,17 @@
       :else expr)))
 
 (define
-  sx-eval-page
+  sx-expr-to-str
   (fn
-    (path-expr env)
-    (cek-try
-      (fn
-        ()
-        (let
-          ((exprs (sx-parse path-expr)))
-          (when
-            (not (empty? exprs))
-            (let
-              ((expr (if (= (len exprs) 1) (first exprs) exprs))
-                (quoted (sx-auto-quote expr env))
-                (callable (if (symbol? quoted) (list quoted) quoted)))
-              (eval-expr callable env)))))
-      (fn (err) nil))))
+    (expr)
+    (cond
+      (string? expr)
+      (str "\"" expr "\"")
+      (symbol? expr)
+      (symbol-name expr)
+      (list? expr)
+      (str "(" (join " " (map sx-expr-to-str expr)) ")")
+      :else (str expr))))
 
 (define
   sx-handle-request
@@ -46,50 +28,48 @@
     (path headers env)
     (let
       ((is-ajax (or (has-key? headers "sx-request") (has-key? headers "hx-request")))
-        (path-expr (sx-url-to-expr path))
-        (page-ast (sx-eval-page path-expr env)))
+        (raw-sx
+          (if
+            (or (= path "/sx/") (= path "/"))
+            "(home)"
+            (slice path 4 (len path))))
+        (page-sx-raw (replace raw-sx "." " "))
+        (page-exprs (sx-parse page-sx-raw))
+        (page-expr (if (empty? page-exprs) nil (first page-exprs)))
+        (page-sx
+          (if
+            (nil? page-expr)
+            page-sx-raw
+            (sx-expr-to-str (sx-auto-quote page-expr env))))
+        (layout-sx (str "(~layouts/doc :path \"" path "\" " page-sx ")")))
       (if
-        (nil? page-ast)
-        nil
+        is-ajax
         (let
-          ((nav-path (if (starts-with? path "/sx/") path (str "/sx" path))))
-          (cek-try
-            (fn
-              ()
-              (if
-                is-ajax
-                (let
-                  ((content (list (make-symbol "~layouts/doc") :path nav-path page-ast)))
-                  (render-to-html content env))
-                (let
-                  ((wrapped (list (make-symbol "~layouts/doc") :path nav-path page-ast))
-                    (full-ast
-                      (list
-                        (make-symbol "~shared:layout/app-body")
-                        :content wrapped))
-                    (body-html (render-to-html full-ast env)))
-                  (render-to-html
-                    (list
-                      (make-symbol "~shared:shell/sx-page-shell")
-                      :title "SX"
-                      :csrf ""
-                      :page-sx (serialize full-ast)
-                      :body-html body-html
-                      :component-defs __shell-component-defs
-                      :component-hash __shell-component-hash
-                      :pages-sx __shell-pages-sx
-                      :sx-css __shell-sx-css
-                      :sx-css-classes __shell-sx-css-classes
-                      :asset-url __shell-asset-url
-                      :sx-js-hash __shell-sx-js-hash
-                      :body-js-hash __shell-body-js-hash
-                      :wasm-hash __shell-wasm-hash
-                      :head-scripts __shell-head-scripts
-                      :body-scripts __shell-body-scripts
-                      :inline-css __shell-inline-css
-                      :inline-head-js __shell-inline-head-js
-                      :init-sx __shell-init-sx
-                      :use-wasm true
-                      :meta-html "")
-                    env))))
-            (fn (err) (str "<h1>Render error</h1><pre>" err "</pre>"))))))))
+          ((full-sx (render-to-sx (first (sx-parse layout-sx)) env)))
+          full-sx)
+        (let
+          ((body-html (render-to-html (first (sx-parse layout-sx)) env)))
+          (render-to-html
+            (quasiquote
+              (~shared:shell/sx-page-shell
+                :title "sx"
+                :csrf ""
+                :page-sx (unquote layout-sx)
+                :body-html (unquote body-html)
+                :component-defs (unquote (env-get env "__shell-component-defs"))
+                :component-hash (unquote (env-get env "__shell-component-hash"))
+                :pages-sx (unquote (env-get env "__shell-pages-sx"))
+                :sx-css (unquote (env-get env "__shell-sx-css"))
+                :sx-css-classes (unquote (env-get env "__shell-sx-css-classes"))
+                :asset-url (unquote (env-get env "__shell-asset-url"))
+                :sx-js-hash (unquote (env-get env "__shell-sx-js-hash"))
+                :body-js-hash (unquote (env-get env "__shell-body-js-hash"))
+                :wasm-hash (unquote (env-get env "__shell-wasm-hash"))
+                :head-scripts nil
+                :body-scripts nil
+                :inline-css nil
+                :inline-head-js nil
+                :init-sx nil
+                :use-wasm true
+                :meta-html ""))
+            env))))))