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/core/src/session/step_context.rs

@@ -2,11 +2,11 @@ use std::sync::Arc;
 
 use crate::agents_md::LoadedAgentsMd;
 use crate::environment_selection::TurnEnvironmentSnapshot;
-use crate::session::McpRuntimeSnapshot;
 use crate::session::turn_context::TurnContext;
 use crate::tools::router::ToolRouter;
 use codex_exec_server::ExecutorCapabilityDiscoverySnapshot;
 use codex_exec_server::ResolvedSelectedCapabilityRoot;
+use codex_mcp::McpBinding;
 use codex_mcp::ToolInfo;
 
 /// Request-scoped state that may change between model sampling requests.
@@ -17,8 +17,8 @@ pub(crate) struct StepContext {
     pub(crate) selected_capability_roots: Vec<ResolvedSelectedCapabilityRoot>,
     /// Executor-materialized capability files shared by MCP and skills in this exact step.
     pub(crate) executor_capability_discovery: Option<Arc<ExecutorCapabilityDiscoverySnapshot>>,
-    /// The exact MCP config and manager used to advertise and execute tools for this step.
-    pub(crate) mcp: Arc<McpRuntimeSnapshot>,
+    /// The exact MCP connections, configuration, and catalog captured for this step.
+    pub(crate) mcp: Arc<McpBinding>,
     /// The fixed MCP tool list used for this exact sampling request.
     pub(crate) mcp_tools: Vec<ToolInfo>,
     /// The finalized tool plan advertised and executed for this exact sampling request.