collect: fix last_broadcast tracking and diff condition

Always compute the payload (diff or full snapshot) regardless of
last_broadcast state, and store the broadcast payload — not the raw
snapshot — as last_broadcast so subsequent diffs are based on what
was actually sent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/collect.py

@@ -89,12 +89,12 @@ def run(args: argparse.Namespace) -> None:
                     apply_procedural(snapshot)
                     store["records"].append(snapshot)
                     save_store(out, store, args.max_records)
-                    if args.diff and last_broadcast:
+                    if args.diff:
                         payload = jay_diff_full(last_broadcast, snapshot, combine_upd_add=True)
                     else:
                         payload = snapshot
+                    last_broadcast = payload
                     network.broadcast(payload, push_clients, push_lock)
-                    last_broadcast = snapshot
                     log.info("Record #%d saved at %s", len(store["records"]), snapshot["ts"])
                 except KeyboardInterrupt:
                     raise