[codex] allow disabling environment context injection (#16745)

This adds an `include_environment_context` config/profile flag that
defaults on, and guards both initial injection and later environment
updates to allow skipping injection of `<environment_context>`.

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

@@ -1339,6 +1339,45 @@ async fn omits_apps_guidance_when_configured_off() {
     );
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn omits_environment_context_when_configured_off() {
+    let server = MockServer::start().await;
+    let resp_mock = mount_sse_once(
+        &server,
+        sse(vec![ev_response_created("resp1"), ev_completed("resp1")]),
+    )
+    .await;
+
+    let mut builder = test_codex().with_config(|config| {
+        config.include_environment_context = false;
+    });
+    let codex = builder
+        .build(&server)
+        .await
+        .expect("create new conversation")
+        .codex;
+
+    codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "hello".into(),
+                text_elements: Vec::new(),
+            }],
+            final_output_json_schema: None,
+        })
+        .await
+        .unwrap();
+
+    wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
+
+    let request = resp_mock.single_request();
+    assert!(
+        !message_input_text_contains(&request, "user", "<environment_context>"),
+        "did not expect environment context when include_environment_context = false, got {:?}",
+        request.body_json()["input"]
+    );
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn skills_append_to_developer_message() {
     skip_if_no_network!();