[Feature] Expose the target service name to global predeploy/postdeploy hooks

[qiaozha]

Summary

Global predeploy / postdeploy hooks fire around every azd deploy, but azd does not tell the hook which service triggered the deploy. There's no standard, azd-provided signal naming the current target.

Why it matters

We rely on global hooks for cross-cutting concerns that must run regardless of which service was deployed (e.g. agent RBAC + a new Foundry version, Logic App workflow PUT). But some of that logic must branch per service — e.g. only run the agent's az acr build when the target is the agent, only apply a slot repoint for the relevant service.

Running azd deploy backend vs. azd deploy frontend vs. azd deploy agent-server all invoke the same global predeploy.ts with no first-class way to know the target.

Current workaround

We maintain our own AZD_DEPLOY_SERVICE env-var convention that we set/read ourselves so the global hook can branch. This is:

• untyped / ad-hoc — a string convention, easy to typo, invisible in azure.yaml
• brittle — can drift out of sync with what azd is actually deploying
• non-discoverable — nothing documents that the global hook secretly branches on a service name

Ask

Provide a standard signal to global hooks naming the service currently being deployed — e.g. a well-known env var (AZD_SERVICE_NAME) set for the duration of the hook, and/or a --service <name> value surfaced consistently to global pre/postdeploy.

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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.