diff --git a/backend/.dockerignore b/backend/.dockerignore
index 2c96eb1..a443985 100644
--- a/backend/.dockerignore
+++ b/backend/.dockerignore
@@ -1,2 +1,3 @@
 target/
-Cargo.lock
+# Note: do NOT exclude Cargo.lock here. It is committed (this is a binary crate)
+# and the Dockerfile must COPY it for reproducible dependency resolution.