f71ba11d4c
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.