diff --git a/packages/effect-codex-app-server/src/client.test.ts b/packages/effect-codex-app-server/src/client.test.ts
index 842f15c0e912c..c5fb8fe999247 100644
--- a/packages/effect-codex-app-server/src/client.test.ts
+++ b/packages/effect-codex-app-server/src/client.test.ts
@@ -1,15 +1,20 @@
+import * as Deferred from "effect/Deferred";
 import * as Exit from "effect/Exit";
 import * as Layer from "effect/Layer";
+import * as Logger from "effect/Logger";
 import * as Path from "effect/Path";
 import * as Effect from "effect/Effect";
+import * as Queue from "effect/Queue";
 import * as Ref from "effect/Ref";
+import * as References from "effect/References";
 import * as Scope from "effect/Scope";
 import { ChildProcess, ChildProcessSpawner } from "effect/process";
 
 import * as NodeServices from "@effect/platform-node/NodeServices";
-import { assert, it } from "@effect/vitest";
+import { assert, expect, it } from "@effect/vitest";
 
 import * as CodexClient from "./client.ts";
+import { makeInMemoryStdio } from "./_internal/stdio.ts";
 
 const mockPeerPath = Effect.map(Effect.service(Path.Path), (path) =>
   path.join(import.meta.dirname, "../test/fixtures/codex-app-server-mock-peer.ts"),
@@ -155,4 +160,52 @@ it.layer(NodeServices.layer)("effect-codex-app-server client", (it) => {
       assert.equal(initialized.userAgent, "mock-codex-app-server");
     }),
   );
+
+  it.effect("warns once about a notification that fails to decode and keeps dispatching", () =>
+    Effect.gen(function* () {
+      const secret = "codex-notification-secret-sentinel";
+      const { stdio, input } = yield* makeInMemoryStdio();
+      const warnings: Array<unknown> = [];
+      const client = yield* CodexClient.make(stdio).pipe(
+        Effect.provide(
+          Logger.layer([
+            Logger.make(({ logLevel, fiber }) => {
+              if (logLevel === "Warn")
+                warnings.push(fiber.getRef(References.CurrentLogAnnotations));
+            }),
+          ]),
+        ),
+      );
+      const delivered = yield* Deferred.make<unknown>();
+      yield* client.handleServerNotification("item/agentMessage/delta", (payload) =>
+        Deferred.succeed(delivered, payload).pipe(Effect.asVoid),
+      );
+
+      const send = (params: unknown) =>
+        Queue.offer(
+          input,
+          new TextEncoder().encode(
+            `${JSON.stringify({ method: "item/agentMessage/delta", params })}\n`,
+          ),
+        );
+      const malformed = { itemId: "item-1", threadId: "thread-1", turnId: secret };
+      yield* send(malformed);
+      yield* send(malformed);
+      yield* send({ delta: "ok", itemId: "item-1", threadId: "thread-1", turnId: "turn-1" });
+
+      assert.deepEqual(yield* Deferred.await(delivered), {
+        delta: "ok",
+        itemId: "item-1",
+        threadId: "thread-1",
+        turnId: "turn-1",
+      });
+      assert.lengthOf(warnings, 1);
+      expect(warnings[0]).toMatchObject({
+        operation: "decode-notification-payload",
+        method: "item/agentMessage/delta",
+        issueKinds: expect.arrayContaining(["MissingKey"]),
+      });
+      assert.notInclude(JSON.stringify(warnings), secret);
+    }),
+  );
 });
diff --git a/packages/effect-codex-app-server/src/client.ts b/packages/effect-codex-app-server/src/client.ts
index e7c5f50b57045..8ad690bde946d 100644
--- a/packages/effect-codex-app-server/src/client.ts
+++ b/packages/effect-codex-app-server/src/client.ts
@@ -150,6 +150,29 @@ export const make = Effect.fn("effect-codex-app-server/CodexAppServerClient.make
       >
     | undefined => CodexRpc.CLIENT_NOTIFICATION_PARAMS[method] as never;
 
+  // A notification the schema rejects has no reply to fail, so it is dropped.
+  // A Codex build that drifted from the generated schema repeats the bad shape
+  // on every frame, so each distinct failure is warned about once per client.
+  const warnedDecodeFailures = new Set<string>();
+  const warnUndecodableNotification = (error: CodexError.CodexAppServerProtocolParseError) => {
+    const key = `${error.method}\n${error.issueKinds?.join(",")}`;
+    if (warnedDecodeFailures.has(key)) {
+      return Effect.void;
+    }
+    warnedDecodeFailures.add(key);
+    return Effect.logWarning("Dropped a Codex App Server notification that failed to decode").pipe(
+      Effect.annotateLogs({
+        operation: error.operation,
+        ...(error.method === undefined ? {} : { method: error.method }),
+        ...(error.issueCount === undefined ? {} : { issueCount: error.issueCount }),
+        ...(error.issueKinds === undefined ? {} : { issueKinds: error.issueKinds }),
+        ...(error.maximumPathDepth === undefined
+          ? {}
+          : { maximumPathDepth: error.maximumPathDepth }),
+      }),
+    );
+  };
+
   const dispatchNotification = (
     notification: CodexProtocol.CodexAppServerIncomingNotification,
   ): Effect.Effect<void, never> => {
@@ -163,6 +186,7 @@ export const make = Effect.fn("effect-codex-app-server/CodexAppServerClient.make
 
     if (schema) {
       return decodeNotificationPayload(notification.method, schema, notification.params).pipe(
+        Effect.tapError(warnUndecodableNotification),
         Effect.flatMap((decoded) =>
           Effect.forEach(handlers, (handler) => handler(decoded), { discard: true }),
         ),