diff --git a/AGENTS.md b/AGENTS.md
index 977199212..fb8c9f8fa 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -16,6 +16,7 @@
 
 - Read files in full before wide-ranging changes, before editing files you have not fully inspected, and when asked to investigate or audit. Do not rely on search snippets for broad changes.
 - No `any` unless absolutely necessary.
+- No runtime checks of values whose types TypeScript already guarantees (no `typeof`/`instanceof`/`Array.isArray`/shape guards on typed parameters, typed callback results or typed declarations). Validate only at decided trust boundaries (wire input, schema-checked arguments and params).
 - Inline single-line helpers that have only one call site.
 - Check node_modules for external API types; don't guess.
 - **No inline imports** (`await import()`, `import("pkg").Type`, dynamic type imports). Top-level imports only.