honor incremental ckpt

[yokofly]

Please write user-readable short description of the changes:
fix #1079

  -- Source streams
  DROP STREAM IF EXISTS orders;
  DROP STREAM IF EXISTS products;

  CREATE STREAM orders(order_id int32, product_id int32, quantity int32);
  CREATE STREAM products(product_id int32, name string)
      PRIMARY KEY product_id SETTINGS mode='versioned_kv';

  -- Target stream
  DROP STREAM IF EXISTS enriched_orders;
  CREATE STREAM enriched_orders(order_id int32, product_name string, quantity int32);

  -- MV with join using hybrid hash join and incremental checkpoint
  DROP VIEW IF EXISTS mv_join_incr_ckpt;

  CREATE MATERIALIZED VIEW mv_join_incr_ckpt
  INTO enriched_orders
  AS
  SELECT
      o.order_id,
      p.name AS product_name,
      o.quantity
  FROM orders AS o
  INNER JOIN products AS p ON o.product_id = p.product_id
  SETTINGS
      seek_to = 'earliest',
      checkpoint_interval = 2,
      default_hash_join = 'hybrid',
      checkpoint_settings = 'type=auto;incremental=true';

  -- Insert product data
  INSERT INTO products(product_id, name) VALUES (1, 'Widget'), (2, 'Gadget');

  -- Insert orders
  INSERT INTO orders(order_id, product_id, quantity) VALUES (100, 1, 5), (101, 2, 3);

  -- Wait for epoch 1 checkpoint
  SELECT sleep(3) FORMAT Null;

  -- Insert more data to trigger activity for epoch 2
  INSERT INTO orders(order_id, product_id, quantity) VALUES (102, 1, 10);

  -- Wait for epoch 2 checkpoint (incremental should kick in here)
  SELECT sleep(3) FORMAT Null;

  -- Insert more data for epoch 3
  INSERT INTO orders(order_id, product_id, quantity) VALUES (103, 2, 7);

  -- Wait for epoch 3 checkpoint
  SELECT sleep(3) FORMAT Null;

old:

2026.01.07 04:44:27.708451 [ 220 ] {.mv-047c9b6a-1fa9-4ac1-8e32-0dc7a987929b} <Information> RocksCheckpoint: Took 13 ms to materialized rocks ckpt to 
.mv-047c9b6a-1fa9-4ac1-8e32-0dc7a987929b/3_01KEBCAFJQN2GNX0430PCBDPM2/1.rckpt on disk local_fs_ckpt_storage (/var/lib/proton/checkpoint/), materialized_bytes=2
2026.01.07 04:44:27.708507 [ 220 ] {.mv-047c9b6a-1fa9-4ac1-8e32-0dc7a987929b} <Information> LocalFileSystemCheckpointStorage: Committed checkpoint 
epoch=3_01KEBCAFJQN2GNX0430PCBDPM2 for query=.mv-047c9b6a-1fa9-4ac1-8e32-0dc7a987929b

new:

2026.01.07 04:42:04.211291 [ 5826 ] {.mv-8e9f4216-34cc-4547-b601-fcf461ffb70e} <Information> RocksCheckpoint: Took 12 ms to materialized incremental rocks ckpt to 
.mv-8e9f4216-34cc-4547-b601-fcf461ffb70e/3_01KEBC63H429WKM6YEXZSM1Z09/1.rckpt on disk local_fs_ckpt_storage (./proton-data/checkpoint/), materialized_bytes=2
2026.01.07 04:42:04.211340 [ 5826 ] {.mv-8e9f4216-34cc-4547-b601-fcf461ffb70e} <Information> LocalFileSystemCheckpointStorage: Committed checkpoint 
epoch=3_01KEBC63H429WKM6YEXZSM1Z09 for query=.mv-8e9f4216-34cc-4547-b601-fcf461ffb70e

Epoch	Old Version	New Version
1	materialized rocks ckpt	materialized rocks ckpt
2	materialized rocks ckpt	materialized incremental rocks ckpt
3	materialized rocks ckpt	materialized incremental rocks ckpt

The difference is the word "incremental" in the log message:

Old (broken):
RocksCheckpoint: Took 12 ms to materialized rocks ckpt to ...

New (fixed):
RocksCheckpoint: Took 10 ms to materialized incremental rocks ckpt to ...

The old version was ignoring the incremental=true setting and always doing full checkpoints. Now correctly enables incremental checkpointing for epoch 2+.

[yokofly]

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