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>

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})))`);