Document the optional @embed model kwarg, the query-time same-space rejection, model-string strictness, and the loud schema-apply refusal on model change. Mark RFC-012 phases 1-4 implemented.
Records the design for one resolved EmbeddingConfig behind a sealed Provider enum (OpenAiCompatible primary, covering OpenRouter as the default gateway, OpenAI direct, and self-hosted endpoints; native Gemini for task-type asymmetry; Mock). Identity recorded in the schema IR with query-time same-space validation, NFR floor (deadline, observability, single normalize), and a 5-phase rollout. Corrects the prior handoff's misdiagnosis (the OpenAI client it blamed was dead code).
Links from docs/dev/index.md.
