diff --git a/CLAUDE.md b/CLAUDE.md
index 1ea80e5..e9bafd0 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -72,7 +72,9 @@ Key for every link = `link_type::link_to` (Type ∈ DocType/Report/Page).
   produce hide/block sets cached on `frappe.local`; `_raw_workspaces()` +
   `added_links()`/`order_map()`/`apply_order()` are the structural (always-on) overlay.
   `is_enforcing()`: production → always; design machine → `not is_editing()`
-  (Redis key `jey_layout_editing`). Tolerates missing refs.
+  (Redis key `jey_layout_editing`). `is_design_mode()` defaults to ON exactly when
+  the `jey_layout` app is installed (test machines); `jey_design_mode` in
+  site_config overrides (0/1). Tolerates missing refs.
 - `desk_overrides.py` — wraps `get_workspace_sidebar_items`/`get_desktop_page` via
   `override_whitelisted_methods`. `get_desktop_page` does inject → reorder (always)
   → hide/block filter (only when enforcing). `_build_link_item` shapes an injected
diff --git a/jey_theme/desk_layout.py b/jey_theme/desk_layout.py
index cced9d1..4fc82c9 100644
--- a/jey_theme/desk_layout.py
+++ b/jey_theme/desk_layout.py
@@ -58,7 +58,22 @@ def link_key(link_type: str, link_to: str) -> str:
 # Mode helpers
 # ---------------------------------------------------------------------------
 def is_design_mode() -> bool:
-	return bool(frappe.conf.get("jey_design_mode"))
+	"""Design machines run the editor; production just enforces the snapshot.
+
+	Default: ON exactly when the `jey_layout` editor app is installed (it's only
+	installed on test/design machines). An explicit `jey_design_mode` in
+	site_config overrides this either way (set 0 to force off, 1 to force on)."""
+	override = frappe.conf.get("jey_design_mode")
+	if override is not None:
+		return bool(override)
+	cached = getattr(frappe.local, "_jey_design_mode", None)
+	if cached is None:
+		try:
+			cached = "jey_layout" in frappe.get_installed_apps()
+		except Exception:
+			cached = False
+		frappe.local._jey_design_mode = cached
+	return cached
 
 
 def is_editing() -> bool: