Empty a default and create its partition in one transaction

Telegraf never stops writing. Clearing 50 defaults with separate
TRUNCATEs left the earliest ones refilled by the time maintenance tried
to attach today's child, which then failed on the default's constraint
and aborted the whole run. Doing both under one transaction makes the
concurrent inserts wait and land in the new partition.

salt/postgres/tools/sbin/so-telegraf-repair

@@ -183,16 +183,30 @@ fi
 
 if [[ "$stranded" -gt 0 ]]; then
   echo "Clearing default partitions."
+  # One transaction: Telegraf is still writing, so a default emptied without
+  # its partition in place is refilled before maintenance can attach one.
   psql_tg -v ON_ERROR_STOP=1 <<'EOSQL'
-SELECT format('TRUNCATE TABLE %I.%I', n.nspname, c.relname)
-FROM partman.part_config pc
-JOIN pg_class p ON p.oid = pc.parent_table::regclass
-JOIN pg_inherits i ON i.inhparent = p.oid
-JOIN pg_class c ON c.oid = i.inhrelid
-JOIN pg_namespace n ON n.oid = c.relnamespace
-WHERE pc.parent_table LIKE 'telegraf.%'
-  AND pg_get_expr(c.relpartbound, c.oid) = 'DEFAULT'
-\gexec
+DO $$
+DECLARE
+    r record;
+BEGIN
+    FOR r IN
+        SELECT pc.parent_table,
+               format('%I.%I', n.nspname, c.relname) AS default_table
+        FROM partman.part_config pc
+        JOIN pg_class p ON p.oid = pc.parent_table::regclass
+        JOIN pg_inherits i ON i.inhparent = p.oid
+        JOIN pg_class c ON c.oid = i.inhrelid
+        JOIN pg_namespace n ON n.oid = c.relnamespace
+        WHERE pc.parent_table LIKE 'telegraf.%'
+          AND pg_get_expr(c.relpartbound, c.oid) = 'DEFAULT'
+    LOOP
+        EXECUTE format('TRUNCATE TABLE %s', r.default_table);
+        PERFORM partman.create_partition_time(
+            r.parent_table, ARRAY[date_trunc('day', now())]::timestamptz[]);
+    END LOOP;
+END
+$$;
 EOSQL
 fi