diff --git a/modules/home/skills/system-prompt.md b/modules/home/skills/system-prompt.md
index 0e47b59..fa11499 100644
--- a/modules/home/skills/system-prompt.md
+++ b/modules/home/skills/system-prompt.md
@@ -95,3 +95,8 @@ shifts positional refs. Re-read `jj log` between mutating operations.
 
 **Overcheckpoint.** `jj new` early and often. Frequent cheap checkpoints mean
 mistakes only cost work since the last one.
+
+**Always land on a new commit.** Once a unit of work is done, `jj commit` (or
+`jj describe` then `jj new`) before running anything else. jj snapshots the
+working tree into `@` on every command, so installs, builds, and test runs on
+top of a finished commit silently amend it with whatever they write.