SPA navigation, page component refactors, WASM rebuild

Refactor page components (docs, examples, specs, reference, layouts)
and adapters (adapter-sx, boot-helpers, orchestration) across sx/ and
web/ directories. Add Playwright SPA navigation tests. Rebuild WASM
kernel with updated bytecode. Add OCaml primitives for request handling.

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

tests/playwright/spa-navigation.spec.js

@@ -0,0 +1,90 @@
+// SPA navigation tests — verify header, nav, and content survive navigation
+// Tests that OOB swaps update nav while preserving the header island,
+// and that rendering errors are scoped to #sx-content.
+
+const { test, expect } = require('playwright/test');
+const BASE_URL = process.env.SX_TEST_URL || 'http://localhost:8013';
+
+test.describe('SPA navigation', () => {
+
+  test('header island survives SPA nav to sibling page', async ({ page }) => {
+    await page.goto(BASE_URL + '/sx/(geography.(hypermedia.(example)))', { waitUntil: 'networkidle' });
+
+    // Header should be present and hydrated
+    const headerIsland = page.locator('[data-sx-island="layouts/header"]');
+    await expect(headerIsland).toHaveCount(1);
+    await expect(headerIsland).toContainText('sx');
+
+    // Navigate via SPA
+    await page.click('a[href*="click-to-load"]');
+    await page.waitForURL('**/click-to-load**');
+    await page.waitForTimeout(2000);
+
+    // Header island should still exist
+    await expect(page.locator('[data-sx-island="layouts/header"]')).toHaveCount(1);
+    await expect(page.locator('[data-sx-island="layouts/header"]')).toContainText('sx');
+  });
+
+  test('nav updates via OOB on SPA navigation', async ({ page }) => {
+    await page.goto(BASE_URL + '/sx/(geography.(hypermedia.(example)))', { waitUntil: 'networkidle' });
+
+    // Nav should show current breadcrumbs
+    const nav = page.locator('#sx-nav');
+    await expect(nav).toHaveCount(1);
+    const navTextBefore = await nav.textContent();
+    expect(navTextBefore).toContain('Examples');
+
+    // Navigate to a child page
+    await page.click('a[href*="click-to-load"]');
+    await page.waitForURL('**/click-to-load**');
+    await page.waitForTimeout(2000);
+
+    // Nav should update to show the new page in breadcrumbs
+    const navTextAfter = await page.locator('#sx-nav').first().textContent();
+    expect(navTextAfter).toContain('Click to Load');
+  });
+
+  test('#sx-content exists after SPA navigation', async ({ page }) => {
+    await page.goto(BASE_URL + '/sx/(geography.(hypermedia.(example)))', { waitUntil: 'networkidle' });
+    await expect(page.locator('#sx-content')).toHaveCount(1);
+
+    await page.click('a[href*="click-to-load"]');
+    await page.waitForURL('**/click-to-load**');
+    await page.waitForTimeout(2000);
+
+    // sx-content should still exist (may contain error boundary, but not be missing)
+    await expect(page.locator('#sx-content').first()).toBeAttached();
+  });
+
+  test('rendering error scoped to #sx-content, not full page', async ({ page }) => {
+    await page.goto(BASE_URL + '/sx/(geography.(hypermedia.(example)))', { waitUntil: 'networkidle' });
+
+    // Verify page structure before nav
+    await expect(page.locator('#sx-nav')).toHaveCount(1);
+    await expect(page.locator('#sx-content')).toHaveCount(1);
+
+    await page.click('a[href*="click-to-load"]');
+    await page.waitForURL('**/click-to-load**');
+    await page.waitForTimeout(2000);
+
+    // If there's a render error, it should be inside #sx-content
+    const errors = page.locator('.sx-render-error');
+    const errorCount = await errors.count();
+    if (errorCount > 0) {
+      // Error should be a descendant of #sx-content, not replacing the whole page
+      const errorParent = await errors.first().evaluate(el => {
+        let p = el;
+        while (p) {
+          if (p.id === 'sx-content') return 'sx-content';
+          if (p.id === 'main-panel') return 'main-panel';
+          p = p.parentElement;
+        }
+        return 'unknown';
+      });
+      expect(errorParent).toBe('sx-content');
+
+      // Nav should still be present even with an error
+      await expect(page.locator('#sx-nav').first()).toContainText('Click to Load');
+    }
+  });
+});