fix(app-server): expose remote MCP servers in plugin read (#26453)

## Why

Remote plugin detail responses include MCP server metadata under
`release.mcp_servers`, but Codex did not deserialize or propagate that
field. As a result, `plugin/read` always returned an empty `mcpServers`
list for remote plugins, so the plugin details pane omitted the MCP
Servers section even when the remote plugin declares one.

This affects uninstalled plugins as well: the remote detail API is the
source of truth and returns MCP server keys without requiring a local
plugin bundle.

## What changed

- Deserialize MCP server entries from remote plugin detail responses.
- Normalize their keys into a sorted, deduplicated list on
`RemotePluginDetail`.
- Return those keys from app-server `plugin/read` instead of hardcoding
an empty list.
- Add regression coverage proving an uninstalled remote plugin returns
its MCP server names.

## Test plan

- `just test -p codex-core-plugins`
- `just test -p codex-app-server plugin_read`

codex-rs/app-server/src/request_processors/plugins.rs

@@ -2026,7 +2026,7 @@ fn remote_plugin_detail_to_info(
             .collect(),
         hooks: Vec::new(),
         apps,
-        mcp_servers: Vec::new(),
+        mcp_servers: detail.mcp_servers,
     }
 }
 

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

@@ -122,7 +122,7 @@ async fn plugin_read_rejects_multiple_read_sources() -> Result<()> {
 }
 
 #[tokio::test]
-async fn plugin_read_reads_remote_plugin_details_when_remote_plugin_is_disabled() -> Result<()> {
+async fn plugin_read_returns_remote_mcp_servers_when_uninstalled() -> Result<()> {
     let codex_home = TempDir::new()?;
     let server = MockServer::start().await;
     std::fs::write(
@@ -148,22 +148,31 @@ plugins = true
 
     let detail_body = r#"{
   "id": "plugins~Plugin_00000000000000000000000000000000",
-  "name": "linear",
+  "name": "example-plugin",
   "scope": "GLOBAL",
   "installation_policy": "AVAILABLE",
   "authentication_policy": "ON_USE",
   "release": {
-    "display_name": "Linear",
-    "description": "Track work in Linear",
+    "version": "1.2.1",
+    "display_name": "Example Plugin",
+    "description": "Example plugin",
     "app_ids": [],
     "keywords": [],
     "interface": {
-      "short_description": "Plan and track work",
+      "short_description": "Example plugin",
       "capabilities": [],
-      "default_prompt": "Use the legacy Linear prompt",
+      "default_prompt": "Use the legacy example prompt",
       "default_prompts": []
     },
-    "skills": []
+    "skills": [],
+    "mcp_servers": [
+      {
+        "key": "example-server",
+        "metadata": {
+          "command": "example-mcp"
+        }
+      }
+    ]
   }
 }"#;
     let installed_body = r#"{
@@ -211,12 +220,15 @@ plugins = true
     let response: PluginReadResponse = to_response(response)?;
 
     assert_eq!(response.plugin.marketplace_name, "openai-curated-remote");
-    assert_eq!(response.plugin.summary.id, "linear@openai-curated-remote");
+    assert_eq!(
+        response.plugin.summary.id,
+        "example-plugin@openai-curated-remote"
+    );
     assert_eq!(
         response.plugin.summary.remote_plugin_id.as_deref(),
         Some("plugins~Plugin_00000000000000000000000000000000")
     );
-    assert_eq!(response.plugin.summary.name, "linear");
+    assert_eq!(response.plugin.summary.name, "example-plugin");
     assert_eq!(response.plugin.summary.source, PluginSource::Remote);
     assert_eq!(response.plugin.summary.share_context, None);
     assert_eq!(
@@ -226,7 +238,11 @@ plugins = true
             .interface
             .as_ref()
             .and_then(|interface| interface.default_prompt.clone()),
-        Some(vec!["Use the legacy Linear prompt".to_string()])
+        Some(vec!["Use the legacy example prompt".to_string()])
+    );
+    assert_eq!(
+        response.plugin.mcp_servers,
+        vec!["example-server".to_string()]
     );
     Ok(())
 }

codex-rs/core-plugins/src/remote.rs

@@ -167,6 +167,7 @@ pub struct RemotePluginDetail {
     pub app_manifest: Option<JsonValue>,
     pub skills: Vec<RemotePluginSkill>,
     pub app_ids: Vec<String>,
+    pub mcp_servers: Vec<String>,
 }
 
 #[derive(Debug, Clone, PartialEq)]
@@ -417,6 +418,13 @@ struct RemotePluginReleaseResponse {
     interface: RemotePluginReleaseInterfaceResponse,
     #[serde(default)]
     skills: Vec<RemotePluginSkillResponse>,
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    mcp_servers: Vec<RemotePluginMcpServerResponse>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
+struct RemotePluginMcpServerResponse {
+    key: String,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
@@ -948,6 +956,14 @@ async fn build_remote_plugin_detail(
             enabled: !disabled_skill_names.contains(&skill.name),
         })
         .collect();
+    let mut mcp_servers = plugin
+        .release
+        .mcp_servers
+        .iter()
+        .map(|server| server.key.clone())
+        .collect::<Vec<_>>();
+    mcp_servers.sort_unstable();
+    mcp_servers.dedup();
 
     Ok(RemotePluginDetail {
         marketplace_name,
@@ -959,6 +975,7 @@ async fn build_remote_plugin_detail(
         app_manifest: plugin.release.app_manifest,
         skills,
         app_ids: plugin.release.app_ids,
+        mcp_servers,
     })
 }