# ADR-0018: imagegen.Editor — image-to-image as a separate optional interface

**Status:** Accepted — 2026-07-11

## Context

ADR-0016 shipped text-to-image and explicitly deferred img2img. mort's new
llama-swap media tools need "edit this image under this prompt"
(image-to-image with a denoising strength). Two shape questions: does Edit
belong on `imagegen.Model`, and which llama-swap endpoint carries it —
OpenAI-style `/v1/images/edits` (multipart) or A1111-style `/sdapi/v1/img2img`
(JSON)?

## Decision

- **`Editor` is a separate, optional interface** (`Edit(ctx, EditRequest,
  ...EditOption) (*Result, error)`), not a new method on `Model`. Existing
  `Model` implementations keep compiling; callers type-assert
  (`m.(imagegen.Editor)`) or require the capability explicitly.
- `EditRequest` = the generation knobs (prompt, N, size, steps, cfg, negative
  prompt, sampler, seed) plus `Init Image` (required) and `Strength *float64`
  (denoising strength in [0,1]; nil = backend default). Same option/Apply
  conventions; result type is the shared `Result`.
- llama-swap implements it via **`/sdapi/v1/img2img`**, not
  `/v1/images/edits`: the same sd-server build that ignores `seed` on the
  OpenAI images route (the reason txt2img went SDAPI in ADR-0016's
  implementation) applies; the JSON shape is txt2img's plus
  `init_images: ["<b64>"]` + `denoising_strength`, so it reuses `doJSON`
  verbatim, where the OpenAI route is multipart.

## Consequences

- Backends that can't edit simply don't implement `Editor`; no stub methods.
- The init image travels base64-inline in JSON (~33% overhead) — acceptable at
  chat-image sizes; a future backend needing multipart can still satisfy the
  same interface.