bug: notification replaces_id duplicates visible popup instead of updating it

[P-ict0]

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Hyde version

hydebar main @ d055edf

Operating system/version

Arch Linux 7.1.10-arch1-1

Describe the bug

When a notification uses the freedesktop replaces_id mechanism while the original popup is still visible, Hydebar creates an additional popup instead of updating the existing one.

The notification server appears to handle the replacement ID correctly and reuses the existing notification ID. The problem is in the visible popup handling: each NotificationEvent::Received appends a new popup without checking whether a popup with the same notification ID is already on screen.

As a result, multiple visible popups can represent the same notification ID.

Steps To Reproduce

1. Run Hydebar with its native notification popups enabled.
2. Send a notification and retain the notification ID:

id=$(notify-send -p "Replacement test" "First body")

3. Before the first popup expires, replace it using the returned ID:

notify-send -r "$id" "Replacement test" "Updated body"

Expected Behavior

The existing popup should be updated in place rather than a second popup being created.

There should be only one visible popup remaining for the notification ID. Its contents and expiration time should match the replacement notification, and its lifetime should restart from the replacement time.

This matches the freedesktop notification specification of replaces_id.

[P-ict0]

Proposed implementation:

• Add a small popup helper that replaces an already visible popup when a received notification has the same ID, otherwise appends it normally.
• Keep the existing popup's position in the visible stack.
• Rebuild the replacement popup from the new notification so its contents, lifetime, and shown timestamp are refreshed.
• Use the same arrival timestamp for popup insertion/replacement and pruning.
• Add regression tests covering both visible replacement and the normal append path.

Scope would be limited to popup presentation. Notification storage/server replacement behavior would remain unchanged.

I have a minimal implementation ready on a fork and can adjust it if needed before opening the PR. Does this approach look good?