A session switch or draft restore can leave undefined/null holes in the
composer attachments array. AttachmentList was guarded against this in
#49624, but the sibling submit path was not: submitPromptText maps the
same array through attachmentDisplayText/optimisticAttachmentRef and
buildContextText (a.kind / a.label / a.refText), so a hole threw
"Cannot read properties of undefined (reading 'refText')" — an uncaught
renderer error that blanks the chat pane and shows "Desktop app link
offline".
Close the whole bug class:
- attachmentDisplayText / optimisticAttachmentRef no-op on a falsy
attachment (shared chokepoint, also protects thread.tsx drop handler).
- submitPromptText filters falsy entries from the source array, and
buildContextText filters its (possibly post-sync) input before reading
fields.
7e2db0a140