pgpool: Keep local primary_node_id when leader watchdog reports the ini

Keep local primary_node_id when leader watchdog reports the initial -2 sentinel.

When all pgpool nodes in a cluster are stopped and started simultaneously
(e.g. via an admin "restart all pgpool nodes" action), every node initializes
Req_info->primary_node_id to -2 (the sentinel) and then runs
find_primary_node_repeatedly() locally to discover the real primary. The
watchdog elects a LEADER in parallel; the losing nodes transition to STANDBY,
receive SIG_WATCHDOG_STATE_CHANGED, and call sync_backend_from_watchdog() to
pull the leader's view.

If the leader's own find_primary_node_repeatedly() has not finished yet, the
leader serializes its still-uninitialized primary_node_id (-2) and the
standby's existing protective branch only covers -1 (quarantine). The -2
falls through to the else-clause and overwrites the standby's freshly-
determined valid primary_node_id with -2.

sync_backend_from_watchdog() is only re-invoked on SIG_BACKEND_SYNC_REQUIRED,
which is raised only on WD_FAILOVER_END. No subsequent event fires after a
simultaneous restart, so the standby is stuck at -2 indefinitely.

Add a guard that keeps the local primary_node_id when the leader's value is
the -2 initial sentinel.

Reported-by: Emond Papegaaij <emond(dot)papegaaij(at)gmail(dot)com>
Reported-by: Claude Code
Author: Tatsuo Ishii <ishii(at)postgresql(dot)org>
Discussion: https://www.postgresql.org/message-id/CAGXsc%2BZmBoLs3Mz%3DG-Bdm4JJG%2BfH1NpHfR3qVJVwW4eBKWwStQ%40mail.gmail.com
Backpatch-through: v4.3

Branch
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V4_5_STABLE

Details
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https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=bd27378c2c9ac8d1a511f10bf7b8d4708f7b6980

Modified Files
--------------
src/main/pgpool_main.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)