Credential
Builds an EmbeddingService from a user-supplied key.
The embedding counterpart of CredentialLlmServiceFactory, and simpler than it: embedding has one wire protocol worth speaking, so embabel-agent-starter-byok ships a single implementation covering every OpenAI-compatible provider. An application needs one of its own only for a provider that embeds over some other protocol.
ON SCOPE, since the LLM counterpart has to answer this differently. That one is the second of two tiers and the one to reach for last, because it names com.embabel.agent.spi.LlmService - a package application code is asked not to depend on. This one names EmbeddingService, which lives here in com.embabel.common.ai.model alongside the rest of the model API, so there is no SPI type to avoid and no lower tier to prefer: an application with a provider of its own implements this directly.
Return null for a provider this factory does not handle, rather than building something: the platform tries each factory in turn, and a factory that answered for everything would hand back a client pointed at the wrong endpoint for someone else's key.
The platform caches what this returns, per (provider, key, model), so an implementation should build rather than maintain a cache of its own.