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/features/src/lib.rs

@@ -204,6 +204,8 @@ pub enum Feature {
     EnableMcpApps,
     /// Enable MCP protocol version 2026-07-28 support.
     Mcp20260728,
+    /// Let RMCP coordinate OAuth refresh through the configured credential store.
+    McpOAuthRefreshCoordination,
     /// Removed compatibility flag for the legacy Apps MCP path override.
     AppsMcpPathOverride,
     /// Removed compatibility flag retained as a no-op now that tool_search is always enabled.
@@ -1251,6 +1253,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::McpOAuthRefreshCoordination,
+        key: "mcp_oauth_refresh_coordination",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::AppsMcpPathOverride,
         key: "apps_mcp_path_override",