[Feature] Resolve `${VAR}` interpolation in `azure.yaml` `image:` after predeploy hooks run

[qiaozha]

Summary

${VAR} interpolation in azure.yaml (including a service's image:) is resolved at project-load time, which is before predeploy hooks execute. This makes it impossible to point image: at an artifact a predeploy hook produces.

What happens

Our predeploy hook builds a container and produces a fresh immutable tag (e.g. dev-N.0.0) via az acr build. We would like image: to reference that tag through an env var the hook sets:

services:
  agent:
    image: ${AGENT_DEPLOYED_IMAGE}

But because interpolation happens before the hook runs, ${AGENT_DEPLOYED_IMAGE} is empty/stale at the moment azd reads it — so azd can never deploy the just-built immutable tag.

Current workaround

The predeploy hook performs the container repoint itself (az ... config container set) and writes the immutable tag back to .env, bypassing azure.yaml's image: entirely.

Ask

Support late-resolved ${VAR} for fields like image: — resolve interpolation after predeploy hooks run — so a hook can hand azd the tag it just built.

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Context: encountered while deploying a multi-component AI/chat service (App Service + Function App + Logic App + Foundry hosted agent) end-to-end with azd provision/deploy in Azure/azure-sdk-tools tools/sdk-ai-bots/deployment. We currently work around this with a TypeScript hook.