### System details

AMD Ryzen 7 7735HS, Radeon 680M (integrated), Omarchy 4.0.4

### What's wrong?

A tray item goes blank in the bar when its app switches from a coloured icon back to a `-symbolic` one. It stays blank until the app switches to a coloured icon again.

**Steps to reproduce**

1. Save the script below and run it with `python3 tray-repro.py` (needs only `python-gobject`). It registers a tray item and alternates its `IconName` between `repro-symbolic` (white circle) and `repro-colour` (amber circle) every 3 seconds, emitting `NewIcon` each time.
2. Open the tray drawer in the bar (or pin the "Tray repro" item) and watch the icon.

**What happens**

- symbolic (first time): white circle, tinted correctly
- coloured: amber circle
- symbolic again: nothing is drawn, the slot is empty
- coloured again: amber circle is back

So a symbolic icon only renders if the item has never shown a non-symbolic one. Switching between two symbolic icons, or between two coloured icons, works fine.

**Expected**

The symbolic icon is drawn (tinted to the bar foreground) every time.

**Likely cause (untested)**

`TrayIcon` in `shell/plugins/bar/widgets/Tray.qml` toggles both the image's visibility and its layer on the same property:

```qml
visible: !trayIconRoot.symbolic
layer.enabled: trayIconRoot.symbolic
```

with the `MultiEffect` shown only when `symbolic`. The blank appears exactly when that property flips from false back to true on an existing item, so the effect seems to sample an empty texture after the layer is re-enabled. The same code is on `quattro` today.

**Why it matters**

Apps that use a monochrome icon normally and a coloured one for an alert state (the common "needs attention" pattern) lose their icon as soon as the alert clears.

<details>
<summary>tray-repro.py</summary>

```python
#!/usr/bin/python3
"""Tray item that alternates between a symbolic and a coloured icon every 3 seconds."""
import sys, tempfile
from pathlib import Path
from gi.repository import Gio, GLib

icons = Path(tempfile.mkdtemp())
shape = '<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><circle cx="8" cy="8" r="6" fill="%s"/></svg>'
(icons / "repro-symbolic.svg").write_text(shape % "#ffffff")
(icons / "repro-colour.svg").write_text(shape % "#f5a623")
names = ["repro-symbolic", "repro-colour"]
current = 0

XML = """<node><interface name="org.kde.StatusNotifierItem">
  <property name="Category" type="s" access="read"/><property name="Id" type="s" access="read"/>
  <property name="Title" type="s" access="read"/><property name="Status" type="s" access="read"/>
  <property name="IconName" type="s" access="read"/><property name="IconThemePath" type="s" access="read"/>
  <property name="ItemIsMenu" type="b" access="read"/>
  <method name="Activate"><arg type="i" direction="in"/><arg type="i" direction="in"/></method>
  <signal name="NewIcon"/>
</interface></node>"""

def prop(_c, _s, _p, _i, name):
    if name == "ItemIsMenu":
        return GLib.Variant("b", False)
    return GLib.Variant("s", {"Category": "ApplicationStatus", "Id": sys.argv[1] if len(sys.argv) > 1 else "tray-repro", "Title": "Tray repro",
                              "Status": "Active", "IconName": names[current], "IconThemePath": str(icons)}[name])

def call(_c, _s, _p, _i, _m, _a, invocation):
    invocation.return_value(None)

def switch():
    global current
    current = 1 - current
    print("icon:", names[current], flush=True)
    bus.emit_signal(None, "/StatusNotifierItem", "org.kde.StatusNotifierItem", "NewIcon", None)
    return True

bus = Gio.bus_get_sync(Gio.BusType.SESSION)
bus.register_object("/StatusNotifierItem", Gio.DBusNodeInfo.new_for_xml(XML).interfaces[0], call, prop, None)
bus.call_sync("org.kde.StatusNotifierWatcher", "/StatusNotifierWatcher", "org.kde.StatusNotifierWatcher", "RegisterStatusNotifierItem",
              GLib.Variant("(s)", (bus.get_unique_name(),)), None, Gio.DBusCallFlags.NONE, -1, None)
print("icon:", names[current], flush=True)
GLib.timeout_add_seconds(3, switch)
GLib.MainLoop().run()
```

</details>

Seen on Omarchy 4.0.4, quickshell 0.3.1, Hyprland 0.56.2. I have a screenshot of the four states and will attach it below.