diff --git a/skills/test-driven-development/SKILL.md b/skills/test-driven-development/SKILL.md
index 4320d887..46838cc9 100644
--- a/skills/test-driven-development/SKILL.md
+++ b/skills/test-driven-development/SKILL.md
@@ -182,6 +182,16 @@ Confirm:
 
 **Other tests fail?** Fix now.
 
+**"Other tests" means the project's suite, not just your file.** A
+green run of the test you wrote is not a green suite. Before you call
+the change done, run the project's test command (bare `pytest`,
+`npm test`, `cargo test` — whatever the repo uses) even when your task
+named only one test file. A scope statement in your task bounds the
+deliverable, not your verification. Any failure that run shows —
+including one you didn't cause — goes in your report by name; a red
+test you watched scroll past and didn't mention is a report falsified
+by omission.
+
 ### REFACTOR - Clean Up
 
 After green only: