diff --git a/backend/llm.txt b/backend/llm.txt
index 867f07d..9446d79 100644
--- a/backend/llm.txt
+++ b/backend/llm.txt
@@ -255,6 +255,7 @@ This section is framework-agnostic and applies to any Go service layer (regardle
 - Prefer `*_test.go` with table-driven tests and subtests: `t.Run("case", func(t *testing.T) { ... })`.
 - Prefer testing the public API from an external package (`package xxx_test`) unless you must access unexported helpers.
 - Avoid “focused” tests in committed code (e.g. `FocusConvey`, `FIt`, `fit`, `it.only`, or equivalent), because they silently skip other tests.
+- MUST: in service layer tests, **one test method should focus on one service method** only (e.g. `Test_Freeze` covers `Ledger.Freeze`, `Test_Unfreeze` covers `Ledger.Unfreeze`); do not bundle multiple service methods into a single `Test_*` method.
 
 ### 5.4 Isolation rules