Attachments stop sending in the background if app is left (kept open in the background)

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• This isn't a feature request or a discussion topic

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Bug description

When I go to attach a picture or a video (an otherwise large attachment) to a message, once I click "send" I have to wait for the video to process before it actually sends. This isn't the quick "loading" needed to move the video from your camera roll into your message editing field, but rather the time where a circular completion bar appears over the sent video with the spinning "sending" icon on the bottom right of the attachment.

If I send the attachment and keep using Signal, the attachment is able to send in the background. However, if I leave the app (while keeping it open in the background, naturally), the attachment seemingly stops sending. This is evidenced by the fact that when I re-open the app, the slowly-filling circular outline is replaced with a constantly-spinning circular outline, and it won't start sending again until a few moments have passed. This is unfortunate UX, as in other messaging competitors like WhatsApp, attachments will continue to send in the background, even displaying a progress circle on the top of newer iOS devices displaying send progress, and a "retry" button if the attachment fails to send.

Steps to reproduce

• Send a large attachment, e.g. a video, into a Signal chat.
• Leave the chat session by leaving the app (while keeping it open in the background)

Actual result: Describe here what happens after you run the steps above (i.e. the buggy behaviour)

The attachment unexpectedly stops sending, and requires re-opening the chat to resume. The longer the chat's been closed, the longer it seems to take before the attachment starts sending again.

Expected result: Describe here what should happen after you run the steps above (i.e. what would be the correct behaviour)

The attachment continues to send in the background, functionally identical to the behavior of in-transit attachments when the chat is closed, but Signal is left open (i.e. to open some other chat)

Screenshots

N/A, it would just be videos being sent. Happy to drum up specific screenshots if a dev thinks a particular one would be useful!

Device info

Device: iPhone 16

iOS version: 18.5

Signal version: 7.59.1 (789)

Link to debug log

https://debuglogs.org/ios/7.59.1/4ece25b589c0f4514736e1e2b35d266be4a94cd6509a0728ec8a1ea782477b67.zip

The issue names no source file or test entry point. Reproduce the large-attachment send on an iPhone running iOS 18.5, leave Signal in the background, and review the linked debug log for the attachment-send lifecycle. Done means the attachment continues sending while the app is backgrounded and resumes without requiring the chat to be reopened.