diff --git a/AGENTS.md b/AGENTS.md
index ff0efb55970..145e623f175 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -64,6 +64,7 @@ Skills own workflows; root owns hard policy and routing.
 - Tests may use observed examples, but prod literals need a short contract reason.
 - Compatibility is opt-in. "Shipped" means reachable from a release Git tag; main/GitHub/PR/unreleased code is not shipped.
 - Refactor default: one canonical path. Delete the old path unless user explicitly wants compat or the shipped public contract is obvious and cited.
+- Core runtime consumes only current canonical shapes/config/data. Legacy or retired shapes normalize only in doctor/migration code before runtime; no runtime shims, aliases, or fallback readers.
 - Keep old behavior only for an explicit public API/config/plugin SDK/data contract, tagged upgrade path, security/migration boundary, dependency contract, or observed prod state.
 - If unsure, ask before preserving compat. Do not keep aliases, shims, fallback stacks, stale names, or obsolete tests just in case.
 - Tests alone do not make internals contracts. If compat stays, name the contract and migration/removal plan in code, test, or PR.