Mobile: stalled media uploads cannot be cancelled or dismissed

[heyjoenash]

Describe the bug

On Buzz Mobile for iOS, an image upload against a self-hosted relay can remain in the composer indefinitely with no way to cancel it. In the observed case the request eventually failed with:

upload failed (401): {"error":"authentication failed"}

The failed state can be cleared only by leaving or retrying the composer flow. The underlying cause of the 401 is not yet known.

Steps to reproduce

1. Pair Buzz Mobile with a self-hosted community.
2. Connect over cellular.
3. Open a private channel and select a small image from Photos.
4. Observe the attachment progress tile.
5. If the request stalls or authentication fails, try to cancel or dismiss it.

Expected behavior

• A pending upload can be cancelled without leaving the composer.
• An upload that never completes times out with actionable copy.
• A failed-upload message can be dismissed.
• The relay or client log explains why a valid paired member received a 401.

Version and platform

• Buzz Mobile: v0.4.12
• Platform: iOS
• Relay: self-hosted 87b3fcd, behind HTTPS/WSS
• Network: cellular

Logs / additional context

• Messages, search, reconnect, and a separate sanitized relay-side media upload probe succeeded against the same deployment.
• The mobile request alone returned the 401 shown above.
• The relay logs did not expose a corresponding authentication reason at the default log level.
• This appears distinct from the iOS metadata/422 failure fixed in fix(mobile): image upload fails due to unstripped metadata #2185.
• Mobile: no WebSocket stall detection — half-open cellular sockets look connected until force-quit (plus 4 resilience gaps vs desktop) #3224 and fix(mobile): detect half-open relay sockets with client-side ping/pong #3231 cover half-open mobile WebSockets, which may explain slow reconnects but do not cover media-upload cancellation or this 401.
• No matching open issue or PR was found for the upload recovery behavior.

A focused recovery change can add cancellation, timeout, and dismiss controls without weakening relay authentication. The 401 root cause should remain a separate diagnostic follow-up unless it can be reproduced reliably.