fix: include stable entry ID in chat.history messages

Messages returned by readSessionMessages now include the JSONL entry id,
providing stable unique identifiers for each message. This fixes issues
where downstream consumers (like kai-tools) relied on array-index-based
IDs which were unstable when messages were filtered or added.

src/gateway/session-utils.fs.ts

@@ -23,7 +23,7 @@ export function readSessionMessages(
     try {
       const parsed = JSON.parse(line);
       if (parsed?.message) {
-        messages.push(parsed.message);
+        messages.push({ ...parsed.message, id: parsed.id });
       }
     } catch {
       // ignore bad lines