feat: deprecation warning (#5825)

<img width="955" height="311" alt="Screenshot 2025-10-28 at 14 26 25"
src="https://github.com/user-attachments/assets/99729b3d-3bc9-4503-aab3-8dc919220ab4"
/>

codex-rs/core/tests/common/test_codex.rs

@@ -97,11 +97,9 @@ impl TestCodexBuilder {
         let mut config = load_default_config_for_test(home);
         config.cwd = cwd.path().to_path_buf();
         config.model_provider = model_provider;
-        config.codex_linux_sandbox_exe = Some(PathBuf::from(
-            assert_cmd::Command::cargo_bin("codex")?
-                .get_program()
-                .to_os_string(),
-        ));
+        if let Ok(cmd) = assert_cmd::Command::cargo_bin("codex") {
+            config.codex_linux_sandbox_exe = Some(PathBuf::from(cmd.get_program().to_os_string()));
+        }
 
         let mut mutators = vec![];
         swap(&mut self.config_mutators, &mut mutators);

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

@@ -0,0 +1,51 @@
+#![cfg(not(target_os = "windows"))]
+
+use anyhow::Ok;
+use codex_core::features::Feature;
+use codex_core::protocol::DeprecationNoticeEvent;
+use codex_core::protocol::EventMsg;
+use core_test_support::responses::start_mock_server;
+use core_test_support::skip_if_no_network;
+use core_test_support::test_codex::TestCodex;
+use core_test_support::test_codex::test_codex;
+use core_test_support::wait_for_event_match;
+use pretty_assertions::assert_eq;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn emits_deprecation_notice_for_legacy_feature_flag() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = start_mock_server().await;
+
+    let mut builder = test_codex().with_config(|config| {
+        config.features.enable(Feature::StreamableShell);
+        config.features.record_legacy_usage_force(
+            "experimental_use_exec_command_tool",
+            Feature::StreamableShell,
+        );
+        config.use_experimental_streamable_shell_tool = true;
+    });
+
+    let TestCodex { codex, .. } = builder.build(&server).await?;
+
+    let notice = wait_for_event_match(&codex, |event| match event {
+        EventMsg::DeprecationNotice(ev) => Some(ev.clone()),
+        _ => None,
+    })
+    .await;
+
+    let DeprecationNoticeEvent { summary, details } = notice;
+    assert_eq!(
+        summary,
+        "`experimental_use_exec_command_tool` is deprecated. Use `streamable_shell` instead."
+            .to_string(),
+    );
+    assert_eq!(
+        details.as_deref(),
+        Some(
+            "You can either enable it using the CLI with `--enable streamable_shell` or through the config.toml file with `[features].streamable_shell`"
+        ),
+    );
+
+    Ok(())
+}

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

@@ -10,6 +10,7 @@ mod cli_stream;
 mod client;
 mod compact;
 mod compact_resume_fork;
+mod deprecation_notice;
 mod exec;
 mod fork_conversation;
 mod grep_files;