diff --git a/requirements.txt b/requirements.txt
index dc9ca3d..1e8d560 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,6 @@
-cmcp-runtime
-weight-custody-manifest>=0.23.0
+# cmcp-runtime needs a floor. Without one, an unsatisfiable constraint elsewhere in
+# this file makes pip backtrack to 0.1.0 rather than report a conflict, and the demo
+# then dies at startup instead of at install time. See PR body.
+cmcp-runtime>=0.4.0
+weight-custody-manifest>=0.23.0,<0.25.0
 openai>=2.54.0