feat: hot reload mcp servers (#8957)

### Summary
* Added `mcpServer/refresh` command to inform app servers and active
threads to refresh mcpServer on next turn event.
* Added `pending_mcp_server_refresh_config` to codex core so that if the
value is populated, we reinitialize the mcp server manager on the thread
level.
* The config is updated on `mcpServer/refresh` command which we iterate
through threads and provide with the latest config value after last
write.

codex-rs/protocol/src/protocol.rs

@@ -60,6 +60,13 @@ pub struct Submission {
     pub op: Op,
 }
 
+/// Config payload for refreshing MCP servers.
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema)]
+pub struct McpServerRefreshConfig {
+    pub mcp_servers: Value,
+    pub mcp_oauth_credentials_store_mode: Value,
+}
+
 /// Submission operation
 #[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema)]
 #[serde(tag = "type", rename_all = "snake_case")]
@@ -186,6 +193,9 @@ pub enum Op {
     /// Reply is delivered via `EventMsg::McpListToolsResponse`.
     ListMcpTools,
 
+    /// Request MCP servers to reinitialize and refresh cached tool lists.
+    RefreshMcpServers { config: McpServerRefreshConfig },
+
     /// Request the list of available custom prompts.
     ListCustomPrompts,