[codex] Support ui visibility meta for tools (#24700)

## Summary

Adds support for the same ui.visibility metadata as resources

[spec](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/draft/apps.mdx#resource-discovery)

codex-rs/codex-mcp/src/connection_manager.rs

@@ -64,6 +64,7 @@ use rmcp::model::ReadResourceResult;
 use rmcp::model::RequestId;
 use rmcp::model::Resource;
 use rmcp::model::ResourceTemplate;
+use serde_json::Value as JsonValue;
 use tokio::task::JoinSet;
 use tokio_util::sync::CancellationToken;
 use tracing::Instrument;
@@ -72,6 +73,34 @@ use tracing::trace;
 use tracing::trace_span;
 use tracing::warn;
 
+const MCP_UI_META_KEY: &str = "ui";
+const MCP_UI_VISIBILITY_META_KEY: &str = "visibility";
+const MCP_UI_MODEL_VISIBILITY: &str = "model";
+
+/// Returns whether a tool may be included in model-facing tool declarations.
+///
+/// Tools without visibility metadata remain visible.
+/// Tools with visibility metadata are hidden unless they explicitly include `model`.
+///
+/// <https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx#resource-discovery>
+pub fn tool_is_model_visible(tool: &ToolInfo) -> bool {
+    let Some(visibility) = tool
+        .tool
+        .meta
+        .as_deref()
+        .and_then(|meta| meta.get(MCP_UI_META_KEY))
+        .and_then(JsonValue::as_object)
+        .and_then(|ui| ui.get(MCP_UI_VISIBILITY_META_KEY))
+        .and_then(JsonValue::as_array)
+    else {
+        return true;
+    };
+
+    visibility
+        .iter()
+        .any(|target| target.as_str() == Some(MCP_UI_MODEL_VISIBILITY))
+}
+
 /// A thin wrapper around a set of running [`RmcpClient`] instances.
 pub struct McpConnectionManager {
     clients: HashMap<String, AsyncManagedClient>,

codex-rs/codex-mcp/src/lib.rs

@@ -1,4 +1,5 @@
 pub use connection_manager::McpConnectionManager;
+pub use connection_manager::tool_is_model_visible;
 pub use elicitation::ElicitationReviewRequest;
 pub use elicitation::ElicitationReviewer;
 pub use elicitation::ElicitationReviewerHandle;