Record the reference-anchored generation recipe in memory

MEMORY.md

@@ -4,6 +4,14 @@ Session memory for durable decisions, state, and gotchas. Keep concise, remove o
 
 ## Decisions
 
+- **OpenRouter reference-anchored generation (2026-11-03):** the `/v1/images` endpoint takes no
+  input image; the working image-to-image path is `POST /v1/chat/completions` with a
+  `content` array (`{"type": "image_url", "image_url": {"url": "data:...;base64,..."}}`).
+  `google/gemini-2.5-flash-image` honours reference geometry well (kept the El Capitan column
+  rhythm, motto band, banner slots and blade sign from a photo); response images arrive as
+  `message.images[].image_url.url` (data URL) — the parser also falls back to a data URI inside
+  the message text. Implemented in `generate_textures.generate_image(reference_path=...)` and
+  `scene_concepts.py generate --reference`; licence gate + `.refgen.json` provenance sidecar.
 - **Recent-photo research, gitignored (2026-11-03):** Commons geosearch around the El Capitan block
   found usable last-12-months imagery (Dolby billboards 2026-09-30 CC0 x6, Dolby street + fresh star
   2026-07-17 CC0, El Capitan frontage with an impersonator 2026-02-25 CC BY-SA 4.0, Celia Cruz