diff --git a/backend/llm.txt b/backend/llm.txt
index 9446d79..90962b4 100644
--- a/backend/llm.txt
+++ b/backend/llm.txt
@@ -256,6 +256,8 @@ This section is framework-agnostic and applies to any Go service layer (regardle
 - 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.
+- MUST: within that single `Test_<Method>` function, cover the method’s key behavior contracts and boundary conditions via subcases (`Convey` blocks or `t.Run`) so the method’s behavior can be reviewed in one place (do NOT claim to cover “all edge cases”, but cover the important ones).
+- MUST (minimum set): for each service method test, cover at least: happy path; invalid params / precondition failures; insufficient resources / permission denied (if applicable); idempotency/duplicate call behavior (if applicable); and at least one typical persistence/transaction failure branch (if it is hard to simulate reliably, move that branch coverage to a DB-backed integration/e2e test).
 
 ### 5.4 Isolation rules