PlaceholderEmbeddingService

Marks an com.embabel.common.ai.model.EmbeddingService that stands in for a model this deployment does not yet have a key for.

A placeholder embeds nothing. Its only job is to give the platform something to resolve before any key is supplied, so that a BYOK application using RAG or memory starts with zero keys, the same as one that only chats — the counterpart of PlaceholderLlmService.

A placeholder must not report a dimension

This is the difference between this marker and the LLM one, and the reason the marker has to be checked rather than merely caught.

There is no defensible dimension for a placeholder to return. Any number would be used to create a vector index; writes to that index would succeed; and a real model configured later would silently disagree with everything already stored. The failure would surface as bad search results rather than as an error — the worst kind, because nothing points at the cause.

So dimensions fails like every other call. A consumer that provisions a vector index must therefore ask whether there is a model yet and skip, rather than call dimensions and handle the exception: catching means the decision is made from a failure, and a failure cannot be told apart from a provider that is merely unreachable right now.

Ask it through com.embabel.common.ai.model.EmbeddingService.awaitingProviderKey, NOT by testing for this interface. Wrapping is common — event tracking decorates the configured service, applications add layers to hot-swap the model or meter it — and a wrapper around a placeholder is not itself a placeholder, so a type test answers about the outermost layer and reports "there is a model". The property rides through Kotlin's by delegation to any depth. This interface marks the implementation; the property is the question.

Skipping is recoverable. The index is created once a real model is registered — on the next boot, or sooner for a consumer that re-checks, since reading the property costs nothing to repeat. A consumer that wants recovery without a restart must re-resolve the service rather than hold the reference it was given, since the one it holds is the placeholder and stays so.

Implemented by SetupRequiredEmbedding in embabel-agent-byok-autoconfigure. It lives here, next to PlaceholderLlmService, because com.embabel.common.ai.model.ConfigurableModelProvider has to recognise a placeholder without depending on the BYOK module.