feat: support product-scoped plugins. (#15041)

1. Added SessionSource::Custom(String) and --session-source.
  2. Enforced plugin and skill products by session_source.
  3. Applied the same filtering to curated background refresh.

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

@@ -146,6 +146,56 @@ async fn plugin_install_returns_invalid_request_for_not_available_plugin() -> Re
     Ok(())
 }
 
+#[tokio::test]
+async fn plugin_install_returns_invalid_request_for_disallowed_product_plugin() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let repo_root = TempDir::new()?;
+    std::fs::create_dir_all(repo_root.path().join(".agents/plugins"))?;
+    std::fs::write(
+        repo_root.path().join(".agents/plugins/marketplace.json"),
+        r#"{
+  "name": "debug",
+  "plugins": [
+    {
+      "name": "sample-plugin",
+      "source": {
+        "source": "local",
+        "path": "./sample-plugin"
+      },
+      "policy": {
+        "products": ["CHATGPT"]
+      }
+    }
+  ]
+}"#,
+    )?;
+    write_plugin_source(repo_root.path(), "sample-plugin", &[])?;
+    let marketplace_path =
+        AbsolutePathBuf::try_from(repo_root.path().join(".agents/plugins/marketplace.json"))?;
+
+    let mut mcp =
+        McpProcess::new_with_args(codex_home.path(), &["--session-source", "atlas"]).await?;
+    timeout(DEFAULT_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_plugin_install_request(PluginInstallParams {
+            marketplace_path,
+            plugin_name: "sample-plugin".to_string(),
+            force_remote_sync: false,
+        })
+        .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("not available for install"));
+    Ok(())
+}
+
 #[tokio::test]
 async fn plugin_install_force_remote_sync_enables_remote_plugin_before_local_install() -> Result<()>
 {