diff --git a/codex-rs/exec-server/src/noise_relay/message_framing.rs b/codex-rs/exec-server/src/noise_relay/message_framing.rs
index a0ce5bd555a9..0b69f46b486d 100644
--- a/codex-rs/exec-server/src/noise_relay/message_framing.rs
+++ b/codex-rs/exec-server/src/noise_relay/message_framing.rs
@@ -86,3 +86,7 @@ impl JsonRpcMessageDecoder {
         Ok(Some(message_len))
     }
 }
+
+#[cfg(test)]
+#[path = "message_framing_tests.rs"]
+mod tests;
diff --git a/codex-rs/exec-server/src/noise_relay/message_framing_tests.rs b/codex-rs/exec-server/src/noise_relay/message_framing_tests.rs
new file mode 100644
index 000000000000..c3df14bf5622
--- /dev/null
+++ b/codex-rs/exec-server/src/noise_relay/message_framing_tests.rs
@@ -0,0 +1,52 @@
+use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCNotification;
+use pretty_assertions::assert_eq;
+
+use super::JsonRpcMessageDecoder;
+use super::MAX_NOISE_JSONRPC_MESSAGE_LEN;
+use super::NOISE_RECORD_PLAINTEXT_LEN;
+use super::frame_jsonrpc_message;
+use crate::ExecServerError;
+
+#[test]
+fn fragments_and_reassembles_large_jsonrpc_message() {
+    let message = JSONRPCMessage::Notification(JSONRPCNotification {
+        method: "large/test".to_string(),
+        params: Some(serde_json::json!({
+            "data": "x".repeat(128 * 1024),
+        })),
+    });
+    let framed = frame_jsonrpc_message(&message).unwrap();
+    assert!(framed.len() > 128 * 1024);
+
+    let mut decoder = JsonRpcMessageDecoder::default();
+    let mut decoded = Vec::new();
+    for record in framed.chunks(NOISE_RECORD_PLAINTEXT_LEN) {
+        decoded.extend(decoder.push(record).unwrap());
+    }
+
+    assert_eq!(decoded, vec![message]);
+}
+
+#[test]
+fn rejects_declared_message_length_above_limit_without_payload() {
+    let mut decoder = JsonRpcMessageDecoder::default();
+    let declared_len = (MAX_NOISE_JSONRPC_MESSAGE_LEN as u32 + 1).to_be_bytes();
+
+    assert!(matches!(
+        decoder.push(&declared_len),
+        Err(ExecServerError::Protocol(message))
+            if message == "Noise relay JSON-RPC message has invalid length"
+    ));
+}
+
+#[test]
+fn rejects_oversized_plaintext_record() {
+    let mut decoder = JsonRpcMessageDecoder::default();
+
+    assert!(matches!(
+        decoder.push(&vec![0; NOISE_RECORD_PLAINTEXT_LEN + 1]),
+        Err(ExecServerError::Protocol(message))
+            if message == "Noise relay plaintext record exceeds maximum length"
+    ));
+}
diff --git a/codex-rs/exec-server/src/noise_relay/ordered_ciphertext.rs b/codex-rs/exec-server/src/noise_relay/ordered_ciphertext.rs
index dea332ec06fd..f122d4970743 100644
--- a/codex-rs/exec-server/src/noise_relay/ordered_ciphertext.rs
+++ b/codex-rs/exec-server/src/noise_relay/ordered_ciphertext.rs
@@ -79,3 +79,7 @@ impl OrderedCiphertextFrames {
         Ok(())
     }
 }
+
+#[cfg(test)]
+#[path = "ordered_ciphertext_tests.rs"]
+mod tests;
diff --git a/codex-rs/exec-server/src/noise_relay/ordered_ciphertext_tests.rs b/codex-rs/exec-server/src/noise_relay/ordered_ciphertext_tests.rs
new file mode 100644
index 000000000000..6aa86fcdf055
--- /dev/null
+++ b/codex-rs/exec-server/src/noise_relay/ordered_ciphertext_tests.rs
@@ -0,0 +1,52 @@
+use pretty_assertions::assert_eq;
+
+use super::MAX_PENDING_BYTES;
+use super::OrderedCiphertextFrames;
+
+#[test]
+fn releases_ciphertexts_only_in_nonce_order() {
+    let mut frames = OrderedCiphertextFrames::default();
+
+    assert_eq!(
+        frames.push(/*seq*/ 1, b"second".to_vec()).unwrap(),
+        Vec::<Vec<u8>>::new()
+    );
+    assert_eq!(
+        frames.push(/*seq*/ 0, b"first".to_vec()).unwrap(),
+        vec![b"first".to_vec(), b"second".to_vec()]
+    );
+}
+
+#[test]
+fn ignores_duplicate_ciphertexts_without_replacing_buffered_record() {
+    let mut frames = OrderedCiphertextFrames::default();
+
+    assert_eq!(
+        frames.push(/*seq*/ 1, b"first copy".to_vec()).unwrap(),
+        Vec::<Vec<u8>>::new()
+    );
+    assert_eq!(
+        frames.push(/*seq*/ 1, b"replacement".to_vec()).unwrap(),
+        Vec::<Vec<u8>>::new()
+    );
+    assert_eq!(
+        frames.push(/*seq*/ 0, b"zero".to_vec()).unwrap(),
+        vec![b"zero".to_vec(), b"first copy".to_vec()]
+    );
+    assert_eq!(
+        frames.push(/*seq*/ 0, b"duplicate".to_vec()).unwrap(),
+        Vec::<Vec<u8>>::new()
+    );
+}
+
+#[test]
+fn rejects_unbounded_reordering() {
+    let mut frames = OrderedCiphertextFrames::default();
+
+    assert!(frames.push(/*seq*/ 65, Vec::new()).is_err());
+    assert!(
+        frames
+            .push(/*seq*/ 1, vec![0; MAX_PENDING_BYTES + 1])
+            .is_err()
+    );
+}