fix: fix serde_as annotation and verify with test (#3170)

I didn't do https://github.com/openai/codex/pull/3163 correctly the
first time: now verified with a test.

codex-rs/protocol/Cargo.toml

@@ -17,7 +17,7 @@ mime_guess = "2.0.5"
 serde = { version = "1", features = ["derive"] }
 serde_bytes = "0.11"
 serde_json = "1"
-serde_with = "3.14.0"
+serde_with = { version = "3.14.0", features = ["macros", "base64"] }
 strum = "0.27.2"
 strum_macros = "0.27.2"
 tracing = "0.1.41"

codex-rs/protocol/src/protocol.rs

@@ -774,22 +774,22 @@ pub struct ExecCommandEndEvent {
     pub formatted_output: String,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize)]
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq)]
 #[serde(rename_all = "snake_case")]
 pub enum ExecOutputStream {
     Stdout,
     Stderr,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize)]
 #[serde_as]
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq)]
 pub struct ExecCommandOutputDeltaEvent {
     /// Identifier for the ExecCommandBegin that produced this chunk.
     pub call_id: String,
     /// Which stream produced this chunk.
     pub stream: ExecOutputStream,
     /// Raw bytes from the stream (may not be valid UTF-8).
-    #[serde_as(as = "Base64")]
+    #[serde_as(as = "serde_with::base64::Base64")]
     pub chunk: Vec<u8>,
 }
 
@@ -980,4 +980,21 @@ mod tests {
             r#"{"id":"1234","msg":{"type":"session_configured","session_id":"67e55044-10b1-426f-9247-bb680e5fe0c8","model":"codex-mini-latest","history_log_id":0,"history_entry_count":0}}"#
         );
     }
+
+    #[test]
+    fn vec_u8_as_base64_serialization_and_deserialization() {
+        let event = ExecCommandOutputDeltaEvent {
+            call_id: "call21".to_string(),
+            stream: ExecOutputStream::Stdout,
+            chunk: vec![1, 2, 3, 4, 5],
+        };
+        let serialized = serde_json::to_string(&event).unwrap();
+        assert_eq!(
+            r#"{"call_id":"call21","stream":"stdout","chunk":"AQIDBAU="}"#,
+            serialized,
+        );
+
+        let deserialized: ExecCommandOutputDeltaEvent = serde_json::from_str(&serialized).unwrap();
+        assert_eq!(deserialized, event);
+    }
 }