respect workspace option for disabling plugins (#18907)

Respects the workspace setting for plugins in Codex

Plugins menu disappears
Plugins do not load
Plugins do not load in composer

no plugins loaded
<img width="809" height="226" alt="Screenshot 2026-04-23 at 3 20 45 PM"
src="https://github.com/user-attachments/assets/3a4dba8e-69c3-4046-a77e-f13ab77f84b4"
/>


no plugins in menu
<img width="293" height="204" alt="Screenshot 2026-04-23 at 3 20 35 PM"
src="https://github.com/user-attachments/assets/5cb9bf52-ad72-488f-b90c-5eb457da09a3"
/>

codex-rs/app-server/tests/suite/v2/plugin_install.rs

@@ -308,6 +308,72 @@ async fn plugin_install_rejects_invalid_remote_plugin_name() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn plugin_install_rejects_when_workspace_codex_plugins_disabled() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let repo_root = TempDir::new()?;
+    let server = MockServer::start().await;
+    write_plugins_enabled_config_with_base_url(
+        codex_home.path(),
+        &format!("{}/backend-api/", server.uri()),
+    )?;
+    write_chatgpt_auth(
+        codex_home.path(),
+        ChatGptAuthFixture::new("chatgpt-token")
+            .account_id("account-123")
+            .chatgpt_user_id("user-123")
+            .chatgpt_account_id("account-123")
+            .plan_type("team"),
+        AuthCredentialsStoreMode::File,
+    )?;
+    write_plugin_marketplace(
+        repo_root.path(),
+        "debug",
+        "sample-plugin",
+        "./sample-plugin",
+        /*install_policy*/ None,
+        /*auth_policy*/ None,
+    )?;
+    write_plugin_source(repo_root.path(), "sample-plugin", &[])?;
+    let marketplace_path =
+        AbsolutePathBuf::try_from(repo_root.path().join(".agents/plugins/marketplace.json"))?;
+
+    Mock::given(method("GET"))
+        .and(path("/backend-api/accounts/account-123/settings"))
+        .and(header("authorization", "Bearer chatgpt-token"))
+        .and(header("chatgpt-account-id", "account-123"))
+        .respond_with(
+            ResponseTemplate::new(200).set_body_string(r#"{"beta_settings":{"plugins":false}}"#),
+        )
+        .mount(&server)
+        .await;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_plugin_install_request(PluginInstallParams {
+            marketplace_path: Some(marketplace_path),
+            remote_marketplace_name: None,
+            plugin_name: "sample-plugin".to_string(),
+        })
+        .await?;
+
+    let err = timeout(
+        DEFAULT_TIMEOUT,
+        mcp.read_stream_until_error_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+
+    assert_eq!(err.error.code, -32600);
+    assert!(
+        err.error
+            .message
+            .contains("Codex plugins are disabled for this workspace")
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn plugin_install_returns_invalid_request_for_missing_marketplace_file() -> Result<()> {
     let codex_home = TempDir::new()?;
@@ -907,6 +973,22 @@ connectors = true
     )
 }
 
+fn write_plugins_enabled_config_with_base_url(
+    codex_home: &std::path::Path,
+    base_url: &str,
+) -> std::io::Result<()> {
+    std::fs::write(
+        codex_home.join("config.toml"),
+        format!(
+            r#"chatgpt_base_url = "{base_url}"
+
+[features]
+plugins = true
+"#,
+        ),
+    )
+}
+
 fn write_analytics_config(codex_home: &std::path::Path, base_url: &str) -> std::io::Result<()> {
     std::fs::write(
         codex_home.join("config.toml"),