Associating a pg_basebackup .backup file with it's saveset?

PG 16.10

(I'd rather use PgBackRest, but can't due to the fact that
the immutable filesystem where we must store backup files doesn't support
links. 😞)

Thus, I'm archiving WAL files and taking basebackups.

At some point, when I'm ready to delete the oldest basebackup directory,
I'll also of course need to run "pg_archivecleanup /Database/backups/wals
mumble".

The .backup file is not in the pg_wal.tar file, so how do I know which
.backup file to use?

archive_command = '/usr/local/bin/postgres/wal_archive.sh "%p" "%f"'

$ cd /Database/backups/wals
$ dir *backup
-rw------- 1 postgres postgres 341 2025-08-23 08:42:39
000000010000000200000023.00000028.backup
-rw------- 1 postgres postgres 341 2025-08-23 09:24:48
000000010000000200000035.00000028.backup

$ dir /Database/backups/basebackup/
total 0
drwxr-xr-x 2 postgres postgres 113 2025-08-23 08:42:41
2025-08-23_08-42-36_full/
drwxr-xr-x 2 postgres postgres 113 2025-08-23 09:24:50
2025-08-23_09-24-43_full/

$ dir /Database/backups/basebackup/2025-08-23_09-24-43_full/
total 152896
-rw------- 1 postgres postgres 612541 2025-08-23 09:24:48 backup_manifest
-rw------- 1 postgres postgres 153057906 2025-08-23 09:24:48 base.tar.zst
-rw------- 1 postgres postgres 2847732 2025-08-23 09:24:48 pg_wal.tar.xz
-rw-r--r-- 1 postgres postgres 37864 2025-08-23 09:24:50 schemata.tar.xz

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