# ADR-0016: imagegen — a canonical text-to-image interface

**Status:** Accepted — 2026-06-27

## Context

mort needs to generate images (via llama-swap's stable-diffusion.cpp backend),
and majordomo had no image-generation surface. Image generation does not fit
the chat contract: there are no conversation messages, tools, streaming, or
failover-chain semantics — forcing it through `llm.Request`/`llm.Response`/
`llm.Model` would overload that contract with mostly-unused fields. The user
asked for "a new ai image interface as opposed to llm".

## Decision

- A new canonical **leaf package `imagegen`**, parallel to `llm`, re-exported
  from the root (`ImageModel`, `ImageProvider`, `ImageRequest`, `ImageResult`,
  `ImageOption`, plus `WithImageCount`/`WithImageSize`). Providers import
  `imagegen`; mort codes to the interface, not to llama-swap.
- Minimal v1 surface (text-to-image only):
  - `Request{ Prompt string; N int; Size string }` — zero values mean provider
    default (N=0 → backend default count; "" Size → backend default).
  - `Result{ Images []Image; Raw any }`.
  - `Model.Generate(ctx, Request, ...Option) (*Result, error)` and
    `Provider.ImageModel(id, ...ModelOption) (Model, error)`.
  - Functional options + `Request.Apply`, mirroring `llm`.
- **`type Image = llm.ImagePart`** (bytes + MIME). Reusing the chat content type
  means a generated image drops straight back into a chat turn
  (`llm.UserParts(res.Images[0])`) with no conversion — the key interop win.
- Out of scope for v1 (designed-for, deferred): image edits / img2img, the raw
  A1111 SDAPI, masks/seeds/steps, streaming, and registry-level image-model DSN
  resolution (construct the provider directly for now).
- First implementation: `provider/llamaswap`, targeting OpenAI
  `/v1/images/generations` with `response_format: "b64_json"` (bytes inline; we
  never fetch remote URLs — mirrors `ImagePart`'s bytes-only contract).

## Consequences

- Image generation is provider-agnostic from day one; a future OpenAI DALL·E or
  Gemini image backend implements the same interface.
- The narrow interface keeps the door open for richer requests without breaking
  callers (additive fields/options).
- No health/failover for image models yet; if needed it can be added as a
  separate chain type rather than retrofitting the chat chain.

## Update — optional per-request settings

`Request` gained additive optional overrides — `Steps *int`, `CFGScale *float64`,
`NegativePrompt string`, `Sampler string`, `Seed *int64` — with mirror options
(`WithSteps`, …). nil/"" means "leave the backend's per-model default", so the v1
contract is unchanged for callers that don't set them. `provider/llamaswap`
forwards them to sd-server as `steps`/`cfg_scale`/`negative_prompt`/`sample_method`/
`seed` (omitempty). This realizes the "seeds/steps … additive fields" note above;
img2img/masks/streaming remain deferred.

## Update — A1111 txt2img endpoint (seed support)

`provider/llamaswap` now POSTs to sd-server's **`/sdapi/v1/txt2img`** (A1111)
instead of the OpenAI `/v1/images/generations`. That OpenAI endpoint **ignores
`seed`** on the stable-diffusion.cpp build we run — every render of a prompt is
byte-identical, so a batch of N collapses to one image. `/sdapi/v1/txt2img`
honours `seed`, restoring real per-render variety. llama-swap still routes by
the `model` field in the body; `Size` is split into `width`/`height`.