The app is up. The Mac has nothing on :3000.

dc-up starts .devcontainer/docker-compose.yml. That file often has no 3000:3000. The app listens inside; the Mac has nothing on :3000.

dc-forward reconciles owned alpine/socat sidecars on the Docker network. Host socat → 172.x does not work on Colima. Identity is the host+container pair (so 9001:80 stays asymmetric). Requires exactly one labeled app or --id. Any requested mapping that cannot be ensured fails the command (and dc-up after a successful start).

dc-forward                 # reconcile compose `app.ports` + forwardPorts
dc-forward 3000
dc-forward 9001:80
dc-forward --status
dc-forward --stop

dc-up runs this after a successful start (--no-forward / DC_FORWARD=0 skips). dc-down removes workspace-owned sidecars.

dc-db does not change that wanted set. It follows the host port you already wrote on the db service. If that pair is unpublished, it runs dc-forward --id $db HOST:CONTAINER (the db, not the app). No declared map → refuse. It never invents a port and never --take-ports.

dc-up --ports is not “add 3000”. It replaces the whole devcontainer.json.

Host port already allocated

Two projects can publish the same host port (for example both wordpress-mitm on 9001). Compose then fails.

dc-up
# dc-up: host port conflict
#   ports: 9001
#   holders:
#     d11b00f0880b  other-project-wordpress-mitm-1  compose=other
# Stop the holder(s) above and retry dc-up for this folder? [y/N]

Mode	Behavior
TTY	lists holder → ask y/N → stop labeled foreign holders → retry once
dc-up --create-nets	create missing declared external: true nets as a default bridge (does not take ports)
dc-up --take-ports / --yes	same without prompt; only positively labeled foreign stacks/sidecars. --yes also creates missing nets
non-TTY without flag	lists holder + how to re-run; does not stop

Stops other labeled workspaces only. Unlabeled, ambiguous, or inspect-unknown holders are report-only — they are not stopped. Prefer stopping a sibling stack over editing project compose ports.

Flags: dc up --help and dc forward --help.