refactor: inject Topo-generated env vars into process environment once at start-up

[awphi]

Background

#413 introduced compose-style interpolation in deployment_success_message. Originally this was achived by creating env vars in the CLI and injecting them into all docker compose subprocesses and compose-go calls. We downscoped this to only inject at call sites where it was needed i.e. post_deploy.go.

This has had the unfortunate consequence of causing docker compose and compose-go calls to raise a bunch of warnings when your x-topo block contains one of these env vars without a fallback value e.g.

# compose.yaml
services:
  welcome-service:
    platform: linux/arm64
    image: busybox:latest

x-topo:
  deployment_success_message: "Welcome service deployed successfully! Access it at http://${TOPO_TARGET_HOSTNAME}:8080"

❯ go run ../cmd/topo deploy --target localhost
WARN[0000] The "TOPO_TARGET_HOSTNAME" variable is not set. Defaulting to a blank string.
11:10:46 WARN registry transfer is not yet supported with this configuration. Falling back to direct transfer.

┌─ Build images ────────────────────────────────────────
WARN[0000] The "TOPO_TARGET_HOSTNAME" variable is not set. Defaulting to a blank string.
WARN[0000] No services to build

┌─ Pull images ─────────────────────────────────────────
WARN[0000] The "TOPO_TARGET_HOSTNAME" variable is not set. Defaulting to a blank string.
WARN[0000] The "TOPO_TARGET_HOSTNAME" variable is not set. Defaulting to a blank string.
[+] pull 1/1
 ✔ Image busybox:latest Pulled                                                                                        0.7s

┌─ Start services ──────────────────────────────────────
WARN[0000] The "TOPO_TARGET_HOSTNAME" variable is not set. Defaulting to a blank string.
[+] up 1/1
 ✔ Container test-workspace-welcome-service-1 Started                                                                 0.1s

┌─ Deployment Success ──────────────────────────────────
Welcome service deployed successfully! Access it at http://localhost:8080/

Changes

• Reverts back to the original behaviour of feat: support compose-style interpolation in x-topo attributes #413 with a new implementation - we set the env vars once when parsing the --target flag or env var for the entire process. This means the injected env vars are passed to call compose-go calls (that use WithOsEnv) and subprocess invocations.

Checklist

• 🤖 This change is covered by tests as required.
• 🤹 All required manual testing has been performed.
• 📖 All documentation updates are complete.

[muchzill4]

I’m still split between this being horrible and or the best thing ever. On one hand we have global env that gets propagated as such to compose, which is a superset of what this does. On the other, it's implicit arguments between layers and would not work if topo was a web service (it is not!).

I think it is the right call (for now at least!). Let’s see if we find this foot-gunny.