Switch to uuid_v7 and tighten ConversationId usage (#3819)

Make sure conversations have a timestamp.

codex-rs/mcp-server/src/message_processor.rs

@@ -36,7 +36,6 @@ use serde_json::json;
 use std::sync::Arc;
 use tokio::sync::Mutex;
 use tokio::task;
-use uuid::Uuid;
 
 pub(crate) struct MessageProcessor {
     codex_message_processor: CodexMessageProcessor,
@@ -484,8 +483,8 @@ impl MessageProcessor {
                 return;
             }
         };
-        let conversation_id = match Uuid::parse_str(&conversation_id) {
-            Ok(id) => ConversationId::from(id),
+        let conversation_id = match ConversationId::from_string(&conversation_id) {
+            Ok(id) => id,
             Err(e) => {
                 tracing::error!("Failed to parse conversation_id: {e}");
                 let result = CallToolResult {