fix(typeset): sync select controls to persisted state on SPA navigation

assets/typeset-preview.js

@@ -261,6 +261,15 @@ app = rx.App(
     }
   }
 
+  // On SPA re-navigation React remounts the selects at their defaults; pull
+  // the persisted state back into them before re-rendering.
+  function syncAll() {
+    if (!ensureDefaults()) return;
+    syncSelectsToState();
+    applyAll();
+    renderCodeBlocks();
+  }
+
   window.typesetPreview = {
     state: state,
     applyAll: applyAll,
@@ -269,6 +278,7 @@ app = rx.App(
     getThemeTokensCode: getThemeTokensCode,
     getUsageCode: getUsageCode,
     renderCodeBlocks: renderCodeBlocks,
+    syncAll: syncAll,
   };
 
   document.addEventListener("change", function (e) {

native/pages/typeset.py

@@ -243,8 +243,7 @@ def typeset_page():
                     flow: {json.dumps(FLOW_OPTIONS)},
                 }};
                 if (window.typesetPreview) {{
-                    window.typesetPreview.applyAll();
-                    window.typesetPreview.renderCodeBlocks();
+                    window.typesetPreview.syncAll();
                 }}
                 """
             ),

tests/test_typeset_sync.py

@@ -0,0 +1,35 @@
+"""Regression: /typeset on_mount must sync remounted selects to persisted state."""
+
+import pathlib
+import re
+
+from native.pages.typeset import typeset_page
+
+JS = (pathlib.Path(__file__).parent.parent / "assets" / "typeset-preview.js").read_text(
+    encoding="utf-8",
+)
+
+
+def _on_mount_scripts() -> list[str]:
+    chain = typeset_page().event_triggers["on_mount"]
+    scripts = []
+    for event in chain.events:
+        for name_var, val_var in event.args:
+            if getattr(name_var, "_js_expr", None) == "javascript_code":
+                scripts.append(val_var._var_value)
+                break
+    return scripts
+
+
+def test_on_mount_calls_sync_all() -> None:
+    init = _on_mount_scripts()[0]
+    assert "typesetPreview.syncAll()" in init
+    assert "typesetPreview.applyAll()" not in init
+
+
+def test_sync_all_exported_and_syncs_selects() -> None:
+    assert re.search(r"window\.typesetPreview\s*=\s*\{[^}]*\bsyncAll:\s*syncAll", JS)
+    body = re.search(r"function syncAll\(\)\s*\{(.*?)\n  \}", JS, re.S)
+    assert body
+    b = body.group(1)
+    assert b.index("syncSelectsToState()") < b.index("applyAll()") < b.index("renderCodeBlocks()")