The LLM seam and its provider adapters. The interface package (`llm`) owns the abstract service, the content-block vocabulary, and the stream-chunk assembler; the adapters are concrete implementations that register on `ctx.llm`. All **product** packages.
The interface lives at `llm/llm/`; adapters, retry policy, and reusable token meter are flat siblings under the group. Requests route by `provider`, while `model` is passed through to the selected adapter. A new provider adapter joins here and registers one or more provider routes on `ctx.llm` without touching the interface. See [twin LLM adapters](../../.agents/notes/implemented/architecture/2026-06-13-twin-llm-adapters.md) for the contract-validation origin of the two shipping implementations and the [replay token meter Agent Note](../../.agents/notes/implemented/architecture/2026-07-15-replay-token-meter-service.md) for measurement ownership.