Fix WASM kernel deploy: 3.6MB js_of_ocaml → 68KB wasm_of_ocaml

The deployed sx_browser.bc.wasm.js was actually the js_of_ocaml output
(pure JS), not the wasm_of_ocaml loader. Nothing synced the correct
build output from _build/ to shared/static/wasm/.

- sx_build target=ocaml now auto-syncs WASM kernel + JS fallback + assets
- sx-build-all.sh syncs after dune build
- Correct 68KB WASM loader replaces 3.6MB JS imposter

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

hosts/ocaml/bin/mcp_tree.ml

@@ -581,7 +581,8 @@ let rec handle_tool name args =
     in
     let cmd = match target with
       | "ocaml" ->
-        Printf.sprintf "cd %s/hosts/ocaml && eval $(opam env 2>/dev/null) && dune build 2>&1" project_dir
+        let abs_project = if Filename.is_relative project_dir then Sys.getcwd () ^ "/" ^ project_dir else project_dir in
+        Printf.sprintf "cd %s/hosts/ocaml && eval $(opam env 2>/dev/null) && dune build 2>&1 && cp _build/default/browser/sx_browser.bc.wasm.js %s/shared/static/wasm/sx_browser.bc.wasm.js && cp _build/default/browser/sx_browser.bc.js %s/shared/static/wasm/sx_browser.bc.js && cp -r _build/default/browser/sx_browser.bc.wasm.assets %s/shared/static/wasm/" abs_project abs_project abs_project abs_project
       | "js" | _ ->
         let extra = if full then " --extensions continuations --spec-modules types" else "" in
         Printf.sprintf "cd %s && python3 hosts/javascript/cli.py%s --output shared/static/scripts/sx-browser.js 2>&1" project_dir extra

scripts/sx-build-all.sh

@@ -6,6 +6,15 @@ cd "$(dirname "$0")/.."
 
 echo "=== OCaml build ==="
 (cd hosts/ocaml && eval $(opam env 2>/dev/null) && dune build) || { echo "FAIL: OCaml build"; exit 1; }
+
+echo "=== Sync WASM kernel to shared/static/wasm/ ==="
+OCAML_BUILD=hosts/ocaml/_build/default/browser
+cp "$OCAML_BUILD/sx_browser.bc.wasm.js" shared/static/wasm/sx_browser.bc.wasm.js
+cp "$OCAML_BUILD/sx_browser.bc.js" shared/static/wasm/sx_browser.bc.js
+cp -r "$OCAML_BUILD/sx_browser.bc.wasm.assets" shared/static/wasm/
+echo "  WASM loader: $(du -sh shared/static/wasm/sx_browser.bc.wasm.js | cut -f1)"
+echo "  JS fallback: $(du -sh shared/static/wasm/sx_browser.bc.js | cut -f1)"
+
 echo "=== JS browser build ==="
 python3 hosts/javascript/cli.py --output shared/static/scripts/sx-browser.js || { echo "FAIL: JS build"; exit 1; }
 echo "=== JS test build ==="

tests/playwright/navigation.spec.js

@@ -149,6 +149,53 @@ test.describe('Page Navigation', () => {
     expect(afterNav).toBe(advanced);
   });
 
+  test('sx-get link fetches SX not HTML and preserves layout', async ({ page }) => {
+    await loadPage(page, '');
+
+    // Track requests to detect what format the fetch uses
+    const fetches = [];
+    page.on('request', req => {
+      if (req.url().includes('/sx/') && req.resourceType() === 'xhr')
+        fetches.push({ url: req.url(), accept: req.headers()['accept'] || '' });
+    });
+
+    // Mark page so we can detect full reload vs SPA nav
+    await page.evaluate(() => window.__spa_marker = true);
+
+    // Click a nav link (Geography)
+    await page.click('a[sx-get*="(geography)"]');
+    await expect(page).toHaveURL(/geography/, { timeout: 5000 });
+
+    // Must be SPA navigation — marker survives
+    const marker = await page.evaluate(() => window.__spa_marker);
+    expect(marker).toBe(true);
+
+    // The fetch should have been XHR, not a document navigation
+    expect(fetches.length).toBeGreaterThan(0);
+
+    // 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
+      };
+    });
+    expect(layout.verticallyStacked).toBe(true);
+    expect(layout.horizontalOverlap).toBe(true);
+  });
+
   test('header island renders with SSR', async ({ page }) => {
     await loadPage(page, '(geography)');