Flatpak apps silently cancel FileChooser requests causing download failures (Edge, COSMIC + GTK portal conflict)

[MzaGuille]

Summary

On Pop!_OS 24.04 with COSMIC (Wayland), Microsoft Edge installed as a Flatpak silently cancels file downloads when "Ask me what to do with each download" is enabled. The browser either closes the download or the file never completes. No crash occurs — Edge interprets the portal's silent failure as a user cancellation.

Related issue: #285 (same root mechanism: portal sends no Response signal back to the caller)

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Environment

Item	Value
OS	Pop!_OS 24.04 LTS (noble)
Desktop	COSMIC (Wayland)
xdg-desktop-portal	1.18.4
xdg-desktop-portal-cosmic	0.1.0pop1
xdg-desktop-portal-gtk	1.15.1
Edge	146.0.3856.72-1 (Flatpak, com.microsoft.Edge from Flathub)
Flatpak runtime	org.freedesktop.Platform/x86_64/25.08

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Steps to Reproduce

1. Install Microsoft Edge as Flatpak: flatpak install flathub com.microsoft.Edge
2. Open Edge and go to edge://settings/downloads
3. Enable "Ask me what to do with each download"
4. Attempt to download any file from any website

Expected: A file picker dialog appears asking where to save the file.
Actual: Edge silently cancels the download. No dialog appears. A .crdownload partial file may be left in ~/Descargas (Spanish locale XDG download dir).

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Root Cause Analysis

Portal configuration

/usr/share/xdg-desktop-portal/cosmic-portals.conf defines:

[preferred]
default=cosmic;gtk;
org.freedesktop.impl.portal.Secret=gnome-keyring;

This means COSMIC is tried first, GTK as fallback.

What happens at download time

When Edge (Flatpak, Wayland) needs the FileChooser portal to show a save dialog:

1. Edge requests org.freedesktop.portal.FileChooser.SaveFile via D-Bus
2. xdg-desktop-portal routes to the COSMIC backend first
3. The COSMIC portal either fails to show the dialog or returns no Response signal
4. Edge interprets the silence as cancellation and aborts the download
5. A .crdownload partial file is left on disk (confirms the download was initiated but never completed)

Evidence from journal

systemd[...]: xdg-desktop-portal.service: Consumed X CPU time

No segfault, no OOM kill — clean exit, confirming this is a silent protocol failure, not a crash.

Workaround

Disabling "Ask me what to do with each download" in edge://settings/downloads bypasses the FileChooser portal entirely and downloads work correctly. This confirms the portal call is the failure point.

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Additional Notes

• xdg-desktop-portal-gtk declares UseIn=gnome in its .portal file — it was not designed for COSMIC, yet it runs as fallback
• Both backends are installed as automatic dependencies (neither was manually installed by the user)
• The issue appears to share the root cause with FileChooser: clicking outside dialog loses focus but never sends cancel response, freezing the caller app #285: the FileChooser portal does not return a Response to the caller under certain conditions, causing the caller (Flatpak app) to silently cancel the operation

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Impact

Any Flatpak application that uses the FileChooser portal with a "save" dialog (downloads, exports, save-as) may be affected under COSMIC + Wayland. The failure is silent and hard to diagnose for end users new to Linux.