PlaceholderLlmService

Marks an LlmService that stands in for a model this deployment does not yet have a key for.

A placeholder completes nothing. Its only job is to give the platform something to resolve before any key is supplied, so that "no key yet" surfaces as an actionable error at the call that needed an LLM rather than as a failure to start.

The platform treats the presence of a placeholder as the deployment's own statement that keys arrive at runtime, and relaxes exactly one thing on the strength of it: model names in configuration that nothing has registered are expected rather than fatal. Every other deployment keeps failing fast on a name it cannot resolve, because there a name that resolves to nothing is a typo.

Implemented by SetupRequiredLlm in embabel-agent-byok-autoconfigure. It lives here, next to LlmService, because com.embabel.common.ai.model.ConfigurableModelProvider has to recognise a placeholder without depending on the BYOK module - carrying the placeholder without dragging in that module is the reason the module exists.