Send content expression component deps in SX responses for client routing

When a page has a content expression but no data dependency, compute its
transitive component deps and pass them as extra_component_names to
sx_response(). This ensures the client has all component definitions
needed for future client-side route rendering.

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

shared/sx/helpers.py

@@ -456,7 +456,8 @@ def sx_call(component_name: str, **kwargs: Any) -> str:
 
 
 
-def components_for_request(source: str = "") -> str:
+def components_for_request(source: str = "",
+                           extra_names: set[str] | None = None) -> str:
     """Return defcomp/defmacro source for definitions the client doesn't have yet.
 
     Reads the ``SX-Components`` header (comma-separated component names
@@ -464,6 +465,10 @@ def components_for_request(source: str = "") -> str:
     is missing.  If *source* is provided, only sends components needed
     for that source (plus transitive deps).  If the header is absent,
     returns all needed defs.
+
+    *extra_names* — additional component names (``~foo``) to include
+    beyond what *source* references.  Used by ``execute_page`` to send
+    components the page's content expression needs for client-side routing.
     """
     from quart import request
     from .jinja_bridge import _COMPONENT_ENV
@@ -477,6 +482,12 @@ def components_for_request(source: str = "") -> str:
     else:
         needed = None  # all
 
+    # Merge in extra names (e.g. from page content expression deps)
+    if extra_names and needed is not None:
+        needed = needed | extra_names
+    elif extra_names:
+        needed = extra_names
+
     loaded_raw = request.headers.get("SX-Components", "")
     loaded = set(loaded_raw.split(",")) if loaded_raw else set()
 
@@ -510,7 +521,8 @@ def components_for_request(source: str = "") -> str:
 
 
 def sx_response(source: str, status: int = 200,
-                   headers: dict | None = None):
+                   headers: dict | None = None,
+                   extra_component_names: set[str] | None = None):
     """Return an s-expression wire-format response.
 
     Takes a raw sx string::
@@ -520,6 +532,10 @@ def sx_response(source: str, status: int = 200,
     For SX requests, missing component definitions are prepended as a
     ``<script type="text/sx" data-components>`` block so the client
     can process them before rendering OOB content.
+
+    *extra_component_names* — additional component names to include beyond
+    what *source* references.  Used by defpage to send components the page's
+    content expression needs for client-side routing.
     """
     from quart import request, Response
 
@@ -535,7 +551,7 @@ def sx_response(source: str, status: int = 200,
     # For SX requests, prepend missing component definitions
     comp_defs = ""
     if request.headers.get("SX-Request"):
-        comp_defs = components_for_request(source)
+        comp_defs = components_for_request(source, extra_names=extra_component_names)
         if comp_defs:
             body = (f'<script type="text/sx" data-components>'
                     f'{comp_defs}</script>\n{body}')

shared/sx/pages.py

@@ -279,13 +279,25 @@ async def execute_page(
     is_htmx = is_htmx_request()
 
     if is_htmx:
+        # Compute content expression deps so the server sends component
+        # definitions the client needs for future client-side routing
+        extra_deps: set[str] | None = None
+        if page_def.content_expr is not None and page_def.data_expr is None:
+            from .deps import components_needed
+            from .parser import serialize
+            try:
+                content_src = serialize(page_def.content_expr)
+                extra_deps = components_needed(content_src, get_component_env())
+            except Exception:
+                pass  # non-critical — client will just fall back to server
+
         return sx_response(await oob_page_sx(
             oobs=oob_headers if oob_headers else "",
             filter=filter_sx,
             aside=aside_sx,
             content=content_sx,
             menu=menu_sx,
-        ))
+        ), extra_component_names=extra_deps)
     else:
         return await full_page_sx(
             tctx,