The unit tests cover each layer in isolation, but nothing exercised the whole
chain the bug lived in: the real gateway persisting an attachment, SessionDB
holding it after the process exits, and the renderer rebuilding a thumbnail
from the stored turn.
Seeds a session through the real gateway with an image attached, then launches
desktop against it — so the first render is already the relaunch case. Pins
native image routing (the majority path, and the one where a text-only persist
override is dropped) and stages the file behind directory and file names with
spaces, mirroring the macOS composer's Application Support path.
f71ba11d4c