fix(chat): translate session replay cursors

session-stream.mjs

@@ -15,6 +15,26 @@ export function parseSessionStreamLastEventId(value) {
   return id || null;
 }
 
+/**
+ * Portal replay ids are local database cursors and are not necessarily valid
+ * Goose SSE ids. Resume Goose from the newest persisted upstream cursor we
+ * actually know about. If none exists, return null so the caller omits
+ * Last-Event-ID and lets Goose replay the authoritative stream from the start.
+ *
+ * @param {Array<{ upstreamEventId?: string | null }>} events
+ * @param {{ upstreamEventId?: string | null } | null} cursorEvent
+ * @returns {string | null}
+ */
+export function resolveUpstreamResumeEventId(events, cursorEvent = null) {
+  const candidates = Array.isArray(events) ? [...events].reverse() : [];
+  if (cursorEvent) candidates.push(cursorEvent);
+  for (const event of candidates) {
+    const id = String(event?.upstreamEventId ?? '').trim();
+    if (id) return id;
+  }
+  return null;
+}
+
 export function isTerminalSessionEvent(event) {
   const type = String(event?.type ?? '').trim();
   return SESSION_STREAM_TERMINAL_TYPES.has(type);