Bug fix: deduplicate assistant messages (#2758)

We are treating assistant messages in a different way than other
messages which resulted in a duplicated history.

See #2698

codex-rs/core/tests/suite/client.rs

@@ -12,6 +12,7 @@ use codex_login::CodexAuth;
 use core_test_support::load_default_config_for_test;
 use core_test_support::load_sse_fixture_with_id;
 use core_test_support::wait_for_event;
+use serde_json::json;
 use tempfile::TempDir;
 use wiremock::Mock;
 use wiremock::MockServer;
@@ -66,7 +67,6 @@ fn write_auth_json(
     account_id: Option<&str>,
 ) -> String {
     use base64::Engine as _;
-    use serde_json::json;
 
     let header = json!({ "alg": "none", "typ": "JWT" });
     let payload = json!({
@@ -746,3 +746,151 @@ async fn env_var_overrides_loaded_auth() {
 fn create_dummy_codex_auth() -> CodexAuth {
     CodexAuth::create_dummy_chatgpt_auth_for_testing()
 }
+
+/// Scenario:
+/// - Turn 1: user sends U1; model streams deltas then a final assistant message A.
+/// - Turn 2: user sends U2; model streams a delta then the same final assistant message A.
+/// - Turn 3: user sends U3; model responds (same SSE again, not important).
+///
+/// We assert that the `input` sent on each turn contains the expected conversation history
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn history_dedupes_streamed_and_final_messages_across_turns() {
+    // Skip under Codex sandbox network restrictions (mirrors other tests).
+    if std::env::var(CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR).is_ok() {
+        println!(
+            "Skipping test because it cannot execute when network is disabled in a Codex sandbox."
+        );
+        return;
+    }
+
+    // Mock server that will receive three sequential requests and return the same SSE stream
+    // each time: a few deltas, then a final assistant message, then completed.
+    let server = MockServer::start().await;
+
+    // Build a small SSE stream with deltas and a final assistant message.
+    // We emit the same body for all 3 turns; ids vary but are unused by assertions.
+    let sse_raw = r##"[
+        {"type":"response.output_text.delta", "delta":"Hey "},
+        {"type":"response.output_text.delta", "delta":"there"},
+        {"type":"response.output_text.delta", "delta":"!\n"},
+        {"type":"response.output_item.done", "item":{
+            "type":"message", "role":"assistant",
+            "content":[{"type":"output_text","text":"Hey there!\n"}]
+        }},
+        {"type":"response.completed", "response": {"id": "__ID__"}}
+    ]"##;
+    let sse1 = core_test_support::load_sse_fixture_with_id_from_str(sse_raw, "resp1");
+
+    Mock::given(method("POST"))
+        .and(path("/v1/responses"))
+        .respond_with(
+            ResponseTemplate::new(200)
+                .insert_header("content-type", "text/event-stream")
+                .set_body_raw(sse1.clone(), "text/event-stream"),
+        )
+        .expect(3) // respond identically to the three sequential turns
+        .mount(&server)
+        .await;
+
+    // Configure provider to point to mock server (Responses API) and use API key auth.
+    let model_provider = ModelProviderInfo {
+        base_url: Some(format!("{}/v1", server.uri())),
+        ..built_in_model_providers()["openai"].clone()
+    };
+
+    // Init session with isolated codex home.
+    let codex_home = TempDir::new().unwrap();
+    let mut config = load_default_config_for_test(&codex_home);
+    config.model_provider = model_provider;
+
+    let conversation_manager =
+        ConversationManager::with_auth(CodexAuth::from_api_key("Test API Key"));
+    let NewConversation {
+        conversation: codex,
+        ..
+    } = conversation_manager
+        .new_conversation(config)
+        .await
+        .expect("create new conversation");
+
+    // Turn 1: user sends U1; wait for completion.
+    codex
+        .submit(Op::UserInput {
+            items: vec![InputItem::Text { text: "U1".into() }],
+        })
+        .await
+        .unwrap();
+    wait_for_event(&codex, |ev| matches!(ev, EventMsg::TaskComplete(_))).await;
+
+    // Turn 2: user sends U2; wait for completion.
+    codex
+        .submit(Op::UserInput {
+            items: vec![InputItem::Text { text: "U2".into() }],
+        })
+        .await
+        .unwrap();
+    wait_for_event(&codex, |ev| matches!(ev, EventMsg::TaskComplete(_))).await;
+
+    // Turn 3: user sends U3; wait for completion.
+    codex
+        .submit(Op::UserInput {
+            items: vec![InputItem::Text { text: "U3".into() }],
+        })
+        .await
+        .unwrap();
+    wait_for_event(&codex, |ev| matches!(ev, EventMsg::TaskComplete(_))).await;
+
+    // Inspect the three captured requests.
+    let requests = server.received_requests().await.unwrap();
+    assert_eq!(requests.len(), 3, "expected 3 requests (one per turn)");
+
+    // Replace full-array compare with tail-only raw JSON compare using a single hard-coded value.
+    let r3_tail_expected = serde_json::json!([
+        {
+            "type": "message",
+            "id": null,
+            "role": "user",
+            "content": [{"type":"input_text","text":"U1"}]
+        },
+        {
+            "type": "message",
+            "id": null,
+            "role": "assistant",
+            "content": [{"type":"output_text","text":"Hey there!\n"}]
+        },
+        {
+            "type": "message",
+            "id": null,
+            "role": "user",
+            "content": [{"type":"input_text","text":"U2"}]
+        },
+        {
+            "type": "message",
+            "id": null,
+            "role": "assistant",
+            "content": [{"type":"output_text","text":"Hey there!\n"}]
+        },
+        {
+            "type": "message",
+            "id": null,
+            "role": "user",
+            "content": [{"type":"input_text","text":"U3"}]
+        }
+    ]);
+
+    let r3_input_array = requests[2]
+        .body_json::<serde_json::Value>()
+        .unwrap()
+        .get("input")
+        .and_then(|v| v.as_array())
+        .cloned()
+        .expect("r3 missing input array");
+    // skipping earlier context and developer messages
+    let tail_len = r3_tail_expected.as_array().unwrap().len();
+    let actual_tail = &r3_input_array[r3_input_array.len() - tail_len..];
+    assert_eq!(
+        serde_json::Value::Array(actual_tail.to_vec()),
+        r3_tail_expected,
+        "request 3 tail mismatch",
+    );
+}