Chat notifications are upgraded to Communication Notifications and attach
the sender's avatar to the INPerson via downloadAvatarImage. The image was
built with INImage(imageData:), which renders on the iPhone but is not
relayed to paired devices like the Apple Watch. The Watch then falls back to
drawing a monogram from the sender's initials instead of the avatar.
Write the downloaded avatar bytes to a file in the shared App Group
container and back the INImage with INImage(url:) so the system can resolve
the image lazily across devices. Files are named by a stable hash of the
content-addressed thumbnail URL so notifications from the same sender reuse
one file.
Claude
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