Document UI release verification

AGENTS.md

@@ -27,6 +27,20 @@ cargo test --workspace
 Do not weaken or skip these gates to make a commit pass. Fix the underlying
 warning, lint, formatting issue, or test failure.
 
+## UI verification conventions
+
+`TESTING.md` is the source of truth for iOS visual verification and the release
+regression suite.
+
+- Update `TESTING.md` in the same commit whenever UI appearance, behavior,
+  navigation, or interaction changes so its scenarios remain current.
+- For each ordinary commit, run every `TESTING.md` scenario relevant to the
+  changed UI in addition to the required pre-commit gates. Report which visual
+  scenarios were exercised.
+- When asked to perform a release test, run the complete `TESTING.md` checklist.
+  Every scenario must succeed before reporting release sign-off; record failures
+  and resolve release blockers instead of skipping them.
+
 ## iOS simulator build and deployment
 
 This Apple Silicon project builds the simulator app for `arm64`. Do not disable