diff --git a/shared/sx/jinja_bridge.py b/shared/sx/jinja_bridge.py
index 57860a8..35bff0c 100644
--- a/shared/sx/jinja_bridge.py
+++ b/shared/sx/jinja_bridge.py
@@ -349,14 +349,23 @@ def components_for_page(page_sx: str, service: str | None = None) -> tuple[str,
 
     needed = components_needed(page_sx, _COMPONENT_ENV)
 
-    # Include deps for all :data pages so the client can render them
+    # Include deps for :data pages whose component trees are fully pure
+    # (no IO refs). Pages with IO deps must render server-side.
     if service:
         from .pages import get_all_pages
         for page_def in get_all_pages(service).values():
             if page_def.data_expr is not None and page_def.content_expr is not None:
                 content_src = serialize(page_def.content_expr)
                 data_deps = components_needed(content_src, _COMPONENT_ENV)
-                needed |= data_deps
+                # Check if any dep component has IO refs
+                has_io = False
+                for dep_name in data_deps:
+                    comp = _COMPONENT_ENV.get(dep_name)
+                    if isinstance(comp, Component) and comp.io_refs:
+                        has_io = True
+                        break
+                if not has_io:
+                    needed |= data_deps
 
     if not needed:
         return "", ""
@@ -407,7 +416,13 @@ def css_classes_for_page(page_sx: str, service: str | None = None) -> set[str]:
         for page_def in get_all_pages(service).values():
             if page_def.data_expr is not None and page_def.content_expr is not None:
                 content_src = serialize(page_def.content_expr)
-                needed |= components_needed(content_src, _COMPONENT_ENV)
+                data_deps = components_needed(content_src, _COMPONENT_ENV)
+                has_io = any(
+                    isinstance(_COMPONENT_ENV.get(d), Component) and _COMPONENT_ENV.get(d).io_refs
+                    for d in data_deps
+                )
+                if not has_io:
+                    needed |= data_deps
     classes: set[str] = set()
 
     for key, val in _COMPONENT_ENV.items():