support plugin/list. (#13540)

Introduce a plugin/list which reads from local marketplace.json.
Also update the signature for plugin/install.

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

@@ -0,0 +1,66 @@
+use std::time::Duration;
+
+use anyhow::Result;
+use app_test_support::McpProcess;
+use codex_app_server_protocol::PluginInstallParams;
+use codex_app_server_protocol::RequestId;
+use codex_utils_absolute_path::AbsolutePathBuf;
+use pretty_assertions::assert_eq;
+use tempfile::TempDir;
+use tokio::time::timeout;
+
+const DEFAULT_TIMEOUT: Duration = Duration::from_secs(10);
+
+#[tokio::test]
+async fn plugin_install_rejects_relative_marketplace_paths() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_raw_request(
+            "plugin/install",
+            Some(serde_json::json!({
+                "marketplacePath": "relative-marketplace.json",
+                "pluginName": "missing-plugin",
+            })),
+        )
+        .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("Invalid request"));
+    Ok(())
+}
+
+#[tokio::test]
+async fn plugin_install_returns_invalid_request_for_missing_marketplace_file() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    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: AbsolutePathBuf::try_from(
+                codex_home.path().join("missing-marketplace.json"),
+            )?,
+            plugin_name: "missing-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("marketplace file"));
+    assert!(err.error.message.contains("does not exist"));
+    Ok(())
+}