Enforce single-subject neural assets

Strengthen direct text-to-image prompts and negative prompts to reject contact sheets, turnarounds, duplicates, lineups, and alternate views.

app.py

@@ -324,9 +324,10 @@ def build_asset_prompt(role: str, prompt: str, style_hint: str) -> str:
         )
     else:
         asset_instruction = (
-            "Create one complete standalone 2D sprite of the whole subject, centered and fully visible, "
-            "single object, transparent or plain background, readable silhouette. Not a texture map, not a tiled "
-            "pattern, not a material swatch, not a UV unwrap, not a 3D model skin."
+            "Create exactly one complete standalone 2D game character or object, centered and fully visible. "
+            "Show one subject in one pose from one view only; do not create a character sheet, turnaround, lineup, "
+            "or alternate views. Use a transparent or plain background and a readable silhouette. Not a texture map, "
+            "not a tiled pattern, not a material swatch, not a UV unwrap, not a 3D model skin."
         )
     return (
         f"{role} asset: {prompt}. Creative brief: {style_hint}. "
@@ -1541,7 +1542,9 @@ def diffusion_negative_prompt(spec: AssetSpec) -> str:
     common = (
         "texture map, material texture, seamless texture, tiled pattern, uv map, uv unwrap, "
         "3d model texture, normal map, roughness map, diffuse map, sprite sheet, atlas, "
-        "multiple objects, cropped subject, close-up surface, fabric swatch, text, watermark"
+        "character sheet, model sheet, turnaround, lineup, comparison, alternate views, multiple views, "
+        "duplicate subject, repeated subject, pair, group, multiple objects, cropped subject, close-up surface, "
+        "fabric swatch, text, watermark"
     )
     if is_background_spec(spec):
         camera_negative = {
@@ -1657,8 +1660,10 @@ def primary_diffusion_prompt(spec: AssetSpec) -> str:
             "Use connected environmental forms and clean terrain structure. No characters and no decorative overlay."
         )
     return (
-        f"{spec.prompt} One complete isolated game sprite only, centered, fully visible, readable silhouette, "
-        "with its anatomy, body shape, camera angle, and pose derived directly from the written description. "
+        f"{spec.prompt} Exactly one isolated subject only, centered, fully visible, with one pose and one view. "
+        "Do not repeat the subject and do not create a character sheet, turnaround, lineup, or alternate views. "
+        "Use a readable silhouette and derive its anatomy, body shape, camera angle, and pose directly from "
+        "the written description. "
         "Use a plain uniform white studio background for clean extraction. "
         "Add recognizable costume, equipment, materials, and character details. "
         "No scenery, floor, trees, foliage, frame, or environmental props."