OCaml VM browser: safe equality, thunk trampolining, platform functions, nav pipeline

Core runtime fixes:
- Safe equality (=, !=): physical equality for dicts/lambdas/signals,
  structural only for acyclic types. Prevents infinite loops on circular
  signal subscriber chains.
- contains?: same safe comparison (physical first, structural for simple types)
- Thunk trampolining in as_number and to_string: leaked thunks auto-resolve
  instead of showing <thunk> or erroring "Expected number, got thunk"
- Diagnostic first error: shows actual type received

Island hydration fixes:
- adapter-dom.sx: skip scope-emit for spreads inside islands (was tripling classes)
- schedule-idle: wrap callback to absorb requestIdleCallback deadline arg
- home-stepper: remove spread-specific highlighting (all tokens same style per step)

Platform functions (boot-helpers.sx):
- fetch-request: 3-arg interface (config, success-fn, error-fn) with promise chain
- build-request-body: form serialization for GET/POST
- strip-component-scripts / extract-response-css: SX text processing
- Navigation: bind-boost-link, bind-client-route-click via execute-request
- Loading state: show-indicator, disable-elements, clear-loading-state
- DOM extras: dom-remove, dom-attr-list (name/value pairs), dom-child-list (SX list),
  dom-is-active-element?, dom-is-input-element?, dom-is-child-of?, dom-on,
  dom-parse-html-document, dom-body-inner-html, create-script-clone
- All remaining stubs: csrf-token, loaded-component-names, observe-intersection,
  event-source-connect/listen, with-transition, cross-origin?, etc.

Navigation pipeline:
- browser-push-state/replace-state: accept 1-arg (URL only) or 3-arg
- boot.sx: wire popstate listener to handle-popstate
- URL updates working via handle-history + pushState fix

Morph debugging (WIP):
- dom-child-list returns proper SX list (was JS Array)
- dom-query accepts optional root element for scoped queries
- Navigation fetches and renders SX responses, URL updates, but morph
  doesn't replace content div (investigating dom-child-list on new elements)

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

web/boot.sx

@@ -460,9 +460,9 @@
 
 (define run-post-render-hooks :effects [mutation io]
   (fn ()
-    (log-info "run-post-render-hooks:" (len *post-render-hooks*) "hooks")
+    (log-info (str "run-post-render-hooks: " (len *post-render-hooks*) " hooks"))
     (for-each (fn (hook)
-      (log-info "  hook type:" (type-of hook) "callable:" (callable? hook) "lambda:" (lambda? hook))
+      (log-info (str "  hook type: " (type-of hook) " callable: " (callable? hook) " lambda: " (lambda? hook)))
       (cek-call hook nil))
       *post-render-hooks*)))
 
@@ -489,7 +489,10 @@
       (sx-hydrate-elements nil)
       (sx-hydrate-islands nil)
       (run-post-render-hooks)
-      (process-elements nil))))
+      (process-elements nil)
+      ;; Wire up popstate for back/forward navigation
+      (dom-listen (dom-window) "popstate"
+        (fn (e) (handle-popstate 0))))))
 
 
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