fix(agent): flatten transparency onto white before RGB (#114)

A naive convert('RGB') on a palette-with-transparency image (common: character
PNGs on a clear background) lets PIL guess the transparent pixels — black-ish
artifacts that bleed into the crop + the CCIP embedding (and the "should be
converted to RGBA" warning). to_rgb() composites over white first for a clean,
consistent background; used by both stills and video frames.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/fc_agent/media.py

@@ -13,8 +13,23 @@ def is_video(mime: str) -> bool:
     return bool(mime) and (mime.startswith("video/") or mime in {"image/gif"})
 
 
+def to_rgb(img: Image.Image) -> Image.Image:
+    """RGB, flattening any transparency onto white first. A naive convert('RGB')
+    on a palette-with-transparency image (common for character PNGs on a clear
+    background) lets PIL guess the transparent pixels — usually black artifacts
+    that bleed into the crop + the embedding (and the "should be converted to
+    RGBA" warning). Compositing over white gives a clean, consistent background."""
+    if img.mode in ("RGBA", "LA", "PA") or (
+        img.mode == "P" and "transparency" in img.info
+    ):
+        img = img.convert("RGBA")
+        bg = Image.new("RGBA", img.size, (255, 255, 255, 255))
+        return Image.alpha_composite(bg, img).convert("RGB")
+    return img.convert("RGB")
+
+
 def load_image(data: bytes) -> Image.Image:
-    return Image.open(io.BytesIO(data)).convert("RGB")
+    return to_rgb(Image.open(io.BytesIO(data)))
 
 
 def sample_frames(
@@ -44,5 +59,5 @@ def sample_frames(
         names = sorted(n for n in os.listdir(tmp) if n.startswith("f_"))
         for i, name in enumerate(names[:cap]):
             with Image.open(os.path.join(tmp, name)) as im:
-                out.append((round(i * interval, 2), im.convert("RGB")))
+                out.append((round(i * interval, 2), to_rgb(im)))
         return out