Send all responses as sexp wire format with client-side rendering

- Server sends sexp source text, client (sexp.js) renders everything
- SexpExpr marker class for nested sexp composition in serialize()
- sexp_page() HTML shell with data-mount="body" for full page loads
- sexp_response() returns text/sexp for OOB/partial responses
- ~app-body layout component replaces ~app-layout (no raw!)
- ~rich-text is the only component using raw! (for CMS HTML content)
- Fragment endpoints return text/sexp, auto-wrapped in SexpExpr
- All _*_html() helpers converted to _*_sexp() returning sexp source
- Head auto-hoist: sexp.js moves meta/title/link/script[ld+json]
  from rendered body to document.head automatically
- Unknown components render warning box instead of crashing page
- Component kwargs preserve AST for lazy rendering (fixes <> in kwargs)
- Fix unterminated paren in events/sexp/tickets.sexpr

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/browser/app/errors.py

@@ -83,8 +83,6 @@ async def _rich_error_page(errnum: str, message: str, image: str | None = None)
         return None
 
     try:
-        from shared.sexp.helpers import full_page
-
         # Build a minimal context — avoid get_template_context() which
         # calls cross-service fragment fetches that may fail.
         from shared.infrastructure.context import base_context
@@ -110,18 +108,18 @@ async def _rich_error_page(errnum: str, message: str, image: str | None = None)
                 cart_params["user_id"] = ident["user_id"]
             if ident["session_id"] is not None:
                 cart_params["session_id"] = ident["session_id"]
-            cart_mini_html, auth_menu_html, nav_tree_html = await fetch_fragments([
+            cart_mini, auth_menu, nav_tree = await fetch_fragments([
                 ("cart", "cart-mini", cart_params or None),
                 ("account", "auth-menu", {"email": user.email} if user else None),
                 ("blog", "nav-tree", {"app_name": current_app.name, "path": request.path}),
             ])
-            ctx["cart_mini_html"] = cart_mini_html
-            ctx["auth_menu_html"] = auth_menu_html
-            ctx["nav_tree_html"] = nav_tree_html
+            ctx["cart_mini"] = cart_mini
+            ctx["auth_menu"] = auth_menu
+            ctx["nav_tree"] = nav_tree
         except Exception:
-            ctx.setdefault("cart_mini_html", "")
-            ctx.setdefault("auth_menu_html", "")
-            ctx.setdefault("nav_tree_html", "")
+            ctx.setdefault("cart_mini", "")
+            ctx.setdefault("auth_menu", "")
+            ctx.setdefault("nav_tree", "")
 
         # Try to hydrate post data from slug if not already available
         segments = [s for s in request.path.strip("/").split("/") if s]
@@ -150,23 +148,23 @@ async def _rich_error_page(errnum: str, message: str, image: str | None = None)
 
         # Root header (site nav bar)
         from shared.sexp.helpers import (
-            root_header_html, post_header_html,
-            header_child_html, error_content_html,
+            root_header_sexp, post_header_sexp,
+            header_child_sexp, full_page_sexp, sexp_call,
         )
-        hdr = root_header_html(ctx)
+        hdr = root_header_sexp(ctx)
 
         # Post breadcrumb if we resolved a post
         post = (post_data or {}).get("post") or ctx.get("post") or {}
         if post.get("slug"):
             ctx["post"] = post
-            post_row = post_header_html(ctx)
+            post_row = post_header_sexp(ctx)
             if post_row:
-                hdr += header_child_html(post_row)
+                hdr = "(<> " + hdr + " " + header_child_sexp(post_row) + ")"
 
         # Error content
-        error_html = error_content_html(errnum, message, image)
+        error_content = sexp_call("error-content", errnum=errnum, message=message, image=image)
 
-        return full_page(ctx, header_rows_html=hdr, content_html=error_html)
+        return full_page_sexp(ctx, header_rows=hdr, content=error_content)
     except Exception:
         current_app.logger.debug("Rich error page failed, falling back", exc_info=True)
         return None
@@ -245,7 +243,7 @@ def errors(app):
         status = getattr(e, "status_code", 400)
         messages = getattr(e, "messages", [str(e)])
 
-        if request.headers.get("HX-Request") == "true":
+        if request.headers.get("SX-Request") == "true" or request.headers.get("HX-Request") == "true":
             from shared.sexp.jinja_bridge import render as render_comp
             items = "".join(
                 render_comp("error-list-item", message=str(escape(m)))
@@ -267,7 +265,7 @@ def errors(app):
         msg = str(e)
         # Extract service name from "Fragment account/auth-menu failed: ..."
         service = msg.split("/")[0].replace("Fragment ", "") if "/" in msg else "unknown"
-        if request.headers.get("HX-Request") == "true":
+        if request.headers.get("SX-Request") == "true" or request.headers.get("HX-Request") == "true":
             from shared.sexp.jinja_bridge import render as render_comp
             return await make_response(
                 render_comp("fragment-error", service=str(escape(service))),
@@ -287,7 +285,7 @@ def errors(app):
         if isinstance(e, HTTPException):
             status = e.code or 500
 
-        if request.headers.get("HX-Request") == "true":
+        if request.headers.get("SX-Request") == "true" or request.headers.get("HX-Request") == "true":
             return await make_response(
                 "Something went wrong. Please try again.",
                 status,

shared/browser/app/redis_cacher.py

@@ -75,7 +75,7 @@ def make_cache_key(cache_user_id: str) -> str:
     qs = request.query_string.decode() if request.query_string else ""
 
     # Check if this is an HTMX request
-    is_htmx = request.headers.get("HX-Request", "").lower() == "true"
+    is_htmx = request.headers.get("SX-Request", "").lower() == "true" or request.headers.get("HX-Request", "").lower() == "true"
     htmx_suffix = ":htmx" if is_htmx else ""
 
     if qs:

shared/browser/app/utils/htmx.py

@@ -1,46 +1,28 @@
-"""HTMX utilities for detecting and handling HTMX requests."""
+"""SxEngine request detection utilities."""
 
 from quart import request
 
 
 def is_htmx_request() -> bool:
-    """
-    Check if the current request is an HTMX request.
+    """Check if the current request is an SxEngine request."""
+    return request.headers.get("SX-Request", "").lower() == "true"
 
-    Returns:
-        bool: True if HX-Request header is present and true
-    """
-    return request.headers.get("HX-Request", "").lower() == "true"
+
+def is_sx_request() -> bool:
+    """Check if the current request is an SxEngine request."""
+    return request.headers.get("SX-Request", "").lower() == "true"
 
 
 def get_htmx_target() -> str | None:
-    """
-    Get the target element ID from HTMX request headers.
-
-    Returns:
-        str | None: Target element ID or None
-    """
-    return request.headers.get("HX-Target")
+    """Get the target element ID from SX request headers."""
+    return request.headers.get("SX-Target")
 
 
 def get_htmx_trigger() -> str | None:
-    """
-    Get the trigger element ID from HTMX request headers.
-
-    Returns:
-        str | None: Trigger element ID or None
-    """
+    """Get the trigger element ID from request headers."""
     return request.headers.get("HX-Trigger")
 
 
 def should_return_fragment() -> bool:
-    """
-    Determine if we should return a fragment vs full page.
-
-    For HTMX requests, return fragment.
-    For normal requests, return full page.
-
-    Returns:
-        bool: True if fragment should be returned
-    """
+    """Determine if we should return a fragment vs full page."""
     return is_htmx_request()

shared/browser/app/utils/utils.py

@@ -41,7 +41,7 @@ def vary(resp: Response) -> Response:
     """
     v = resp.headers.get("Vary", "")
     parts = [p.strip() for p in v.split(",") if p.strip()]
-    for h in ("HX-Request", "X-Origin"):
+    for h in ("SX-Request", "HX-Request", "X-Origin"):
         if h not in parts:
             parts.append(h)
     if parts: