Finder/OS drops became `@file:/Users/...` refs that only resolve when the
gateway shares the local disk, so on a remote gateway non-image files
(PDF/CSV/Markdown/...) never reached the agent. Route OS drops through the
file.attach / image.attach_bytes upload pipeline — in-app project-tree and
gutter drags stay inline workspace-relative refs — across every drop surface:
the conversation area, the composer form, the contenteditable input, and the
message-edit composer (which still reproduced the bug).
Also:
- upload dropped files eagerly when a session exists, so the card shows a
spinner instead of stalling the send (images stay submit-time to avoid
racing their thumbnail write);
- round the attachment card and drop the monospace detail;
- render image previews from the bytes we already hold, so a pasted/dropped
screenshot shows its thumbnail and previews even when its only on-disk copy
is a transient path (the data URL is not persisted to localStorage).
Supersedes #38615, #41203.
Co-authored-by: LeonSGP <154585401+LeonSGP43@users.noreply.github.com>
Co-authored-by: Teknium <127238744+teknium1@users.noreply.github.com>
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