Centralize thread MCP state in McpRuntime (#34930)

## What changed

- Make `McpRuntime` own the published MCP configuration, connections, elicitation routing, and selected capability roots for a thread.
- Capture immutable MCP bindings for model steps and tool calls so in-flight work keeps a consistent connection set and approval authority while refreshed state is published atomically.
- Mark MCP state dirty when relevant configuration, plugins, environments, authentication, or elicitation capabilities change, then rebuild it before the next sampling request or out-of-band MCP operation.
- Separate config reloads from server invalidation: `ReloadMcpConfig` applies resolved MCP inputs, while `RefreshMcpServers` requests reinitialization from the thread's latest state.

## Testing

- Cover refreshed state visibility for existing turns, stable step bindings, current approval authority, cancelled refresh retries, resource-client reconciliation, and Apps recovery between sampling requests.

GitOrigin-RevId: 59eabb1aa8dc083426bd18ef4d3630508f376401

codex-rs/codex-mcp/src/rmcp_client.rs

@@ -478,19 +478,6 @@ impl AsyncManagedClient {
                     ),
             )
         });
-        if codex_apps_tools_cache_context
-            .as_ref()
-            .is_some_and(ConnectorRuntimeContext::has_current_tools)
-            || tool_catalog_cache_context
-                .as_ref()
-                .is_some_and(McpToolCatalogCacheContext::has_tools)
-        {
-            let startup_task = client.clone();
-            tokio::spawn(async move {
-                let _ = startup_task.await;
-            });
-        }
-
         Self {
             client,
             is_codex_apps_mcp_server,