diff --git a/AGENTS.md b/AGENTS.md
index 1e2947b5a..1e4c6782e 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -74,6 +74,12 @@
 * Accept a little duplication over a restructure. A new function that repeats a few lines of an existing one is a better diff than reshaping the original so both can share it.
 * Put new logic in self-contained functions in the module it belongs to (platform-specific logic in `src/platform/`, with `use` inside the function body to avoid churning shared import blocks). Call sites in shared files (`src/tray.rs`, `src/core_main.rs`, `src/server/connection.rs`, …) should be thin one-line hooks.
 
+### Scope check before touching shared code
+
+* Before changing a shared trait, a shared struct, or the signature of a widely used function, check whether the bug or feature is specific to one path. If it is, keep the change inside that path unless that is impossible, and say in the PR why it was.
+* If an unrelated caller needs `Default::default()`, `None`, or another placeholder solely to satisfy a signature you changed, the diff is too broad: stop and redesign.
+* The expected shape of a fix is a new function in the feature's own module, plus at most a new field or a thin hook in the shared code it needs. Feature-specific state belongs beside the feature's existing state, not in a new abstraction every caller has to learn.
+
 ### Mandatory regression-surface check
 
 Before considering any implementation complete, perform a minimization pass over the final diff.