issue with healthcheck on postgres/alpine 18.4

[hyperfocusedblur]

im runnning postgres alpine latest version in podman with podman-compose
here is my compose file:

volumes:
  pgdata:

services:
  db:
    image: docker.io/library/postgres:alpine
    container_name: postgres_container 
    env_file:
      - .env
    volumes:
      - pgdata:/var/lib/postgresql/data/pgdata
    healthcheck:
      test: ["CMD-SHELL", "pg_isready --dbname=${POSTGRES_DB} --username=${POSTGRES_USER}"]
      interval: 10s
      retries: 5
      timeout: 5s
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 512M
        reservations:
          cpus: '0.25'
          memory: 256M
    shm_size: 128mb
    restart: unless-stopped

.env file

POSTGRES_USER=postgres_user
POSTGRES_PASSWORD=password
POSTGRES_DB=postgres_db

the issue:
healthcheck returns error and condition healthy never arrives. status of the container hangs on 'starting' if i use healtcheck in compose.
however if i manually run pg_isready on the container from host, there seems to be nothing that would indicate that something is 'not healthy'.

in logs, i see that healthcheck command is probably getting this FATAL value from the postgres container:

[db]     | 2026-05-23 13:22:14.761 UTC [1] LOG:  database system is ready to accept connections
[db]     | 2026-05-23 13:22:21.449 UTC [68] FATAL:  database "postgres_user" does not exist // this is when i manually call pg_isready from the host to the container
[db]     | 2026-05-23 13:22:30.899 UTC [70] FATAL:  database "postgres_user" does not exist

however when i run pg_isready from the host i receive this on stdout:

 $ podman exec postgres_container pg_isready -U postgres_user -d posgtres_db
/var/run/postgresql:5432 - accepting connections

also here it looks like the db exists, contrary to logs:

podman exec postgres_container psql -U postgres_user -l
                                                             List of databases
    Name     |     Owner     | Encoding | Locale Provider |  Collate   |   Ctype    | Locale | ICU Rules |        Access privileges
-------------+---------------+----------+-----------------+------------+------------+--------+-----------+---------------------------------
 postgres    | postgres_user | UTF8     | libc            | en_US.utf8 | en_US.utf8 |        |           |
 postgres_db | postgres_user | UTF8     | libc            | en_US.utf8 | en_US.utf8 |        |           |

to me at least, it indicates that there is no error and the database exists. maybe i am missing something