COPY ... ON SEGMENT on REPLICATED tables: FROM returns N× in Greenplum but only 1× in Cloudberry

```sql

-- Cloudberry cluster with 4 segments
-- Greenplum cluster with 4 segments

create table tab_replicated(a int, b int, c int) distributed replicated;
insert into tab_replicated select i, i, i from generate_series(1, 100) i;

copy tab_replicated to '/home/cbdb/tab_replicated_.txt' on segment;
-- Greenplum: COPY 400 | Cloudberry: COPY 400

create table tab_replicated_new(a int, b int, c int) distributed replicated;
copy tab_replicated_new from '/home/cbdb/tab_replicated_.txt' on segment;
-- Greenplum: COPY 400 | Cloudberry: COPY 100 (unexpected)
```

Reproduce the SQL example on four-segment Cloudberry and Greenplum clusters, focusing on COPY ... FROM ... ON SEGMENT for replicated tables. Compare the reported row counts and trace the implementation of this COPY path; done means Cloudberry returns COPY 400, matching Greenplum.

Written by the indexing model from the issue text.