Attaching a picture in mobile native chat gave no visible feedback: the
image uploaded to the host and its path was pasted into the hidden PTY, so
nothing on screen ever showed it was attached.
Defer the TUI paste to send time and hold picked images in composer state,
rendered as a thumbnail tray above the input (spinner while uploading, X
to remove, image-only sends allowed). On send, each ready image's path is
pasted bracketed into the agent TUI right before the message text, matching
the desktop composer-attachment model. The terminal live-input surface keeps
the immediate paste, where the TUI's own input line is the feedback.