diff --git a/packages/client/README.md b/packages/client/README.md
index 784db94..661b870 100644
--- a/packages/client/README.md
+++ b/packages/client/README.md
@@ -20,6 +20,18 @@ const set = useShape(MyShape, scope);   // filtered to what the identity may rea
 await inbox.post(targetInbox, ref);     // deposit (anticipated SDK API)
 ```
 
+## Principle — the polyfill compensates, it never extends
+
+**The polyfill's ONLY reason to exist is to bridge a NextGraph implementation gap
+or a bug.** Every non-SDK surface must map to a capability NextGraph will provide
+natively, and must fall away at that point. The polyfill MUST NOT add functionality
+of its own — no bespoke features, no observability/tooling, no convenience API that
+isn't strictly "NextGraph will do this natively later." The test for any proposed
+addition: *does it compensate a real, exhibited NextGraph gap or bug?* If not, it
+does not belong here — build it in the consumer application, not in the polyfill.
+Corollary: a compensation whose gap is not actually exhibited on the target broker
+is dead weight, not defensive code — it should be removed, not kept "just in case."
+
 What the polyfill adds on top of the real SDK (each emulated for now, native as
 NextGraph matures):
 - Shared-wallet identity (one wallet for everyone; the current identity id is