### poc

```{eval-rst}
.. plantuml::

   @startuml
   title PoC Plan (Activity)
   ' top to bottom direction
   skinparam shadowing false
   start
   :Broker swap:\nPoint CH Kafka engine at X2;
   :Measure rows/s & CPU/row on CH & X2;
   :Enable x2_seq in payload;\nSwitch CH table to ReplacingMergeTree(x2_seq);
   if (Duplicates under retry?) then (No)
     :Confirm EOS-like behavior;
   else (Yes)
     :Adjust producer idempotence /\nMV dedupe logic;
   endif
   :Enable X2 → Iceberg materializer;
   :Run same query in CH from Iceberg\n(backfill/history) vs MergeTree (hot);
   :Compare latency & cost;
   stop
   @enduml