Add reference-anchored concept generation

docs/asset-tooling.md

@@ -192,6 +192,21 @@ Caveats:
   Blender still prints its own version banner before the script runs, so intake scripts should use
   `--json --out <file>` rather than parsing stdout.
 
+### Reference-anchored concept generation
+
+`tools/scene_concepts.py generate --reference <photo>` anchors a concept frame on a real
+photograph: the photo is sent to the OpenRouter multimodal chat endpoint as a base64 data URL
+(`generate_textures.generate_image(reference_path=...)`) with a prompt suffix that pins the
+photographed geometry (column rhythm, band heights, signage placement, camera angle) while the
+prompt restages lighting, weather and people.
+
+Licence gate: the reference must be listed in its `docs/screens/refs/<venue>/SIDECAR.md` row
+(which also supplies the licence and Commons page for provenance). A photo from anywhere else
+requires `--reference-unchecked`, which records `unchecked` in the provenance. Each anchored
+generation writes a `.refgen.json` sidecar next to the frame (`model`, reference file/licence/page,
+geometry suffix) so a concept frame can always be traced back to its evidence photo. Where a
+generated frame and its reference photo disagree, the photo wins for shape.
+
 ### Reference-board research (`refboard`)
 
 `tools/refboard.py` searches, fetches and documents Wikimedia Commons photos of a real location for