Prepare MCP connections for coordinated OAuth refresh (#42128)

## What changed

- Add the under-development `mcp_oauth_refresh_coordination` feature and pin its selected refresh mode to each MCP connection.
- Treat the refresh mode as part of OAuth connection identity so runtime and MCP configuration refreshes reconnect when the mode changes.
- Keep legacy refresh behavior in builds where coordination is unavailable and emit a warning when coordinated mode is selected.

## Testing

- Cover connection replacement when the feature is toggled through both runtime and MCP configuration refresh paths.

GitOrigin-RevId: 89596150f0338e6ede0e712badecea4450831766

codex-rs/core/src/session/mod.rs

@@ -1883,6 +1883,14 @@ impl Session {
             ) {
                 warn!("failed to refresh MCP auth storage config: {err}");
             }
+            if let Err(err) = config.features.set_enabled(
+                Feature::McpOAuthRefreshCoordination,
+                next_config
+                    .features
+                    .enabled(Feature::McpOAuthRefreshCoordination),
+            ) {
+                warn!("failed to refresh MCP OAuth coordination config: {err}");
+            }
             let config = Arc::new(config);
             state.session_configuration.original_config_do_not_use = Arc::clone(&config);
             self.mark_mcp_runtime_dirty();
@@ -1931,6 +1939,14 @@ impl Session {
         ) {
             warn!("failed to refresh MCP auth storage config: {err}");
         }
+        if let Err(err) = config.features.set_enabled(
+            Feature::McpOAuthRefreshCoordination,
+            next_config
+                .features
+                .enabled(Feature::McpOAuthRefreshCoordination),
+        ) {
+            warn!("failed to refresh MCP OAuth coordination config: {err}");
+        }
         state.session_configuration.original_config_do_not_use = Arc::new(config);
         self.mark_mcp_runtime_dirty();
         drop(state);