On Pub and Sub:

CREATE TYPE inner_bad_enum AS ENUM ('v');

CREATE FUNCTION inner_bad_enum_to_json(inner_bad_enum) RETURNS json AS $f$
DECLARE
    big_arr int[];
    nested_result json;
BEGIN
    -- A large, all-NULL array: small storage footprint, huge JSON output
    big_arr := array_fill(NULL::int, ARRAY[130500,1,1,1,1,1]);

    -- UNRELATED call into json.c. Output is discraded
    nested_result := array_to_json(big_arr);

    -- Return something tiny; the large intermediate result is discarded.
    RETURN json_build_object('note', 'nested call above was large internally');
END;
$f$ LANGUAGE plpgsql IMMUTABLE;

CREATE CAST (inner_bad_enum AS json)
    WITH FUNCTION inner_bad_enum_to_json(inner_bad_enum) AS IMPLICIT;

CREATE TYPE outer_composite AS (field1 inner_bad_enum, field2 int);

CREATE TABLE leak_reentry_tab (a int PRIMARY KEY, b outer_composite);



Pub:
INSERT INTO leak_reentry_tab VALUES (1, ROW('v'::inner_bad_enum, 42)::outer_composite);

Sub:
DELETE FROM leak_reentry_tab WHERE a = 1;

Pub:
UPDATE leak_reentry_tab SET a = 1 WHERE a = 1;


I get:
postgres=# select * from pg_conflict.pg_conflict_log_16400;
 relid | schemaname |     relname      | conflict_type  | remote_xid | remote_commit_lsn |         remote_commit_ts         | remote_origin | replica_identity_full | replica_identity |               remote_tuple            
   | local_conflicts | has_omitted_values 
-------+------------+------------------+----------------+------------+-------------------+----------------------------------+---------------+-----------------------+------------------+---------------------------------------
---+-----------------+--------------------
 16392 | public     | leak_reentry_tab | update_missing |        701 | 0/017D5920        | 2026-09-01 10:53:08.752213+05:30 | pg_16400      | f                     | {"a":1}          | {"a":1,"b":{"omitted":true,"length":28
}} |                 | t
(1 row)

See 'b' got ommited even though length is way below threshold.

While 'b' was nothing but : 'note', 'nested call above was large internally'. 
Everything above json_build_object in inner_bad_enum_to_json() was a discaradable output.

If I change code to do this:
json_size_would_exceed(int currentlen, Size addlen)
{
	if (json_size_limit && (Size) currentlen + addlen > json_size_limit)
	{
//		json_size_limit_hit = true;
		json_size_limit_hit = false;
		elog (LOG, "HIT THE LIMIT but not setting limit_hit");

		return true;
	}
	return false;
}

I get remote_tuple correctly reported as:
{"a":1,"b":{"field1":{"note" : "nested call above was large internally"},"field2":42}}
This is to show that, there is nothing wrong with 'b' as such.

~~

Also I noticed that log shows:
DETAIL:  Could not find the row to be updated: remote row (1, (v,42)), replica identity (a)=(1).

While CLT shows 
{"a":1,"b":{"field1":{"note" : "nested call above was large internally"},"field2":42}}

Value of 'b' is different in both.