Session: bring back a taskbar saved on a screen the desktop doesn't have

Plasma 6.2.5 keeps a panel on a screen number and never moves one whose
number is past the screen count, so a taskbar saved on a spare output
(#18, lastScreen=8 with three screens) or on a screen a smaller layout
dropped stayed hidden. Before Plasma starts, session/fix-panels.py moves
such a panel and its tray's containment to screen 0 (the primary),
keeping its widgets, unless screen 0 already has a panel on that edge.
doctor.sh checks the panels' screens, and report.sh lists them with the
live outputs and panels.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/design.md

@@ -185,6 +185,8 @@ KWin renders with OpenGL through zink on Turnip, Vulkan on the same GPU vrcompos
 
 The nested session also runs the system's XDG autostart entries, being a KDE session. Discover's update notifier started `plasma-discover --mode update` in it (520 to 620 MB resident and about 9% of a core, plus `flatpak-system-helper` and AppStream downloads), and IBus started a daemon, the kimpanel panel and its GTK extension that nothing can use: KWin hands text input to the one input method it starts (`ft-textinput`), and the session drops `QT_IM_MODULE`, `GTK_IM_MODULE` and `XMODIFIERS`. The session hides both for this desktop only, with `Hidden=true` copies in its own autostart folder. The geoclue demo agent stays: it's what answers apps' location requests to Geoclue outside GNOME, and it costs nothing while idle. Orca's entry only starts in GNOME-family desktops.
 
+Plasma 6.2.5 keeps each panel on a screen number (`lastScreen` in `plasma-org.kde.plasma.desktop-appletsrc`), and the numbers rank the enabled outputs by priority, so 0 is the primary screen. A panel whose number is past the screen count gets no view, and Plasma never moves it: the remap it runs at every start only moves a panel whose number has no desktop, and this desktop keeps a desktop for every output it has seen, spares included. So the taskbar was lost when the number of screens went down, and once it was found saved on a spare output, number 8 of a desktop with three screens ([#18](https://github.com/DeeJanuz/frametop/issues/18)). Before Plasma starts, the session runs `session/fix-panels.py`, which moves any panel numbered past the screen count, with its system tray's containment, to screen 0, keeping its widgets and settings. A panel stays put when screen 0 already has one on that edge, and comes back by itself if the screens do. The file is backed up to `<file>.ft-bak` first. Plasma's scripting can't do this while it runs (`panel.screen` is read-only in 6.2.5), so a lost taskbar comes back at the desktop's next start. `scripts/doctor.sh` and `scripts/report.sh` list the panels and their screens.
+
 Remote desktop is a chain (krdp, then FreeRDP inside Xvnc) because nothing on SteamOS serves KWin over VNC directly. Kept connected all the time, it cost about a core with nobody watching: krdpserver 55 to 78% (it encodes H.264 in software with openh264: VA-API finds no driver for the Frame's GPU in the container), FreeRDP 16 to 27%, Xvnc 6 to 11%, and the bridge's layout check every 5 seconds another 4%. krdp creates its screencast session per RDP connection and drops it when the connection closes (`SessionController::onNewConnection` in krdp 6.7), so an idle krdpserver costs nothing and can stay up; only the RDP connection has to go. The bridge connects FreeRDP when a VNC client appears and disconnects 45 seconds after the last one leaves. Xvnc has no hook for its clients, so the bridge counts established connections to its port with `ss`, woken early by Xvnc's log output; looking with `ss` once a second cost about 0.9% of a core in bash, against about 0.1% this way. `Xvnc -inetd` from a systemd socket would start a server per connection and lose sharing between viewers. The layout check (`ft-layout remote-view`, which scans `/proc` for plasmashell and runs `kscreen-doctor -j`) now runs only while FreeRDP runs, and then only after `kwinoutputconfig.json` or `frametop-layout.json` changes, with one check a minute in case a change touched neither.
 
 Program names stay within 15 characters, because Linux truncates process names there and the scripts find programs with `pgrep -x` and `pkill -x`. That's why the prefix is `ft-`.
@@ -224,6 +226,5 @@ On the Frame, SteamVR is part of the OS image (`/opt/steamvr`, the `deckard-stea
 
 - A controller button that shows the screens during a game. Games own the controllers, so this needs SteamVR input actions for ft-screens.
 - Drawing KWin's cursor on the screens.
-- Plasma can lose its panels when the number of screens goes down, because they're saved against a screen that no longer exists. Removing `plasma-org.kde.plasma.desktop-appletsrc` and `plasmashellrc` from `~/.config/frametop` brings the default panels back.
 - Frame pacing and GPU cost with several busy screens haven't been measured.
 - Real standby on a stand, with rendering and tracking paused, not just the backlight off. SteamVR has no call for it, and its activity level follows the proximity sensor.

scripts/doctor.sh

@@ -36,6 +36,10 @@ check "distrobox" on_frame 'test -x ~/.local/bin/distrobox && ~/.local/bin/distr
 check "container $FRAME_BOX" on_frame "podman ps -a --filter name=^$FRAME_BOX\$ --format '{{.Image}} {{.Status}}' | grep ."
 check "repo on the Frame" on_frame 'pwd'
 check "free space in ~" on_frame "df -h ~ | awk 'NR==2{print \$4\" free\"}'"
+# A taskbar saved on a screen the desktop doesn't have is hidden; the desktop's next start
+# moves it to the first screen (session/fix-panels.py).
+check "taskbar on a screen" on_frame 'set -o pipefail; [ -f session/fix-panels.py ] || { echo "not checked (older checkout)"; exit 0; }
+  python3 session/fix-panels.py --check | paste -sd ";" | sed "s/;/; /g"'
 
 echo "what Frametop needs from SteamOS:"
 if [ "$FRAME_LOCAL" = 1 ]; then

scripts/report.sh

@@ -42,6 +42,25 @@ for i, s in enumerate(d.get("screens", []), 1):
 print("visibility:", d.get("visibility"))
 PY
 
+section "Plasma panels and outputs"
+python3 "$repo/session/fix-panels.py" --check 2>&1 || true
+python3 - "$repo" <<'PY' 2>&1 || true
+import json, subprocess, sys
+sys.path.insert(0, sys.argv[1] + "/layout")
+import ft_layout
+env = ft_layout.nested_env()
+if not env:
+    sys.exit(print("desktop not running: no live outputs or panels"))
+outs = json.loads(subprocess.run(["kscreen-doctor", "-j"], capture_output=True, text=True, env=env, timeout=10).stdout or "{}")
+for o in outs.get("outputs", []):
+    size = o.get("size") or {}
+    print(f"output {o.get('name')}: enabled={o.get('enabled')} priority={o.get('priority')} {size.get('width')}x{size.get('height')}")
+js = "print(JSON.stringify(panels().map(p => ({id: p.id, screen: p.screen, location: p.location}))))"
+r = subprocess.run(["qdbus6", "org.kde.plasmashell", "/PlasmaShell", "org.kde.PlasmaShell.evaluateScript", js],
+                   capture_output=True, text=True, env=env, timeout=10)
+print("live panels:", (r.stdout or r.stderr).strip())
+PY
+
 section "Input relay (last 60 lines)"
 journalctl --user -u frametop-input-relay -n 60 --no-pager -o short 2>/dev/null
 section "Pointer helper (last 60 lines)"

session/fix-panels.py

@@ -0,0 +1,143 @@
+#!/usr/bin/env python3
+"""Bring back a taskbar that Plasma saved against a screen this desktop doesn't have.
+
+Plasma 6.2.5 ties each panel to a screen number (lastScreen in its containment), and the
+numbers rank the enabled outputs by priority: 0 is the primary screen. A panel whose
+number is past the screen count gets no view and stays hidden; Plasma never moves it,
+even on a later start (sanitizeScreenLayout() only remaps a panel whose number has no
+desktop, and the Frametop desktop keeps a desktop for every spare output it has seen).
+So a taskbar saved on a spare output (issue #18), or on a screen that a smaller layout
+dropped, was lost until the config was deleted.
+
+The session runs this before Plasma starts, so nothing races Plasma for the file. Each
+panel numbered at or past the screen count moves to screen 0, with its system tray's
+containment, and keeps its widgets and settings. A panel is left where it is when screen
+0 already has a panel on that edge: it comes back by itself if the screens do. The file
+is backed up once per repair (<file>.ft-bak), and the changes go through kwriteconfig6.
+
+  fix-panels.py [--screens N] [--file APPLETSRC] [--check]
+    --screens  the desktop's screen count (default: the configured layout's)
+    --file     default: $XDG_CONFIG_HOME/plasma-org.kde.plasma.desktop-appletsrc, with
+               XDG_CONFIG_HOME defaulting to the Frametop desktop's ~/.config/frametop
+    --check    change nothing; list the panels, and exit 1 if one is lost
+"""
+import argparse
+import os
+import re
+import shutil
+import subprocess
+import sys
+
+EDGES = {3: "top", 4: "bottom", 5: "left", 6: "right"}  # Plasma::Types::Location
+SYSTRAY = "org.kde.plasma.private.systemtray"
+GROUP = re.compile(r"\[([^\]]*)\]")
+
+
+def parse(text):
+    """KConfig text -> {(group, subgroup, ...): {key: value}}."""
+    groups, cur = {}, None
+    for line in text.splitlines():
+        line = line.strip()
+        if line.startswith("["):
+            cur = tuple(GROUP.findall(line))
+            groups.setdefault(cur, {})
+        elif cur is not None and "=" in line and not line.startswith("#"):
+            k, v = line.split("=", 1)
+            groups[cur][re.sub(r"\[\$.*\]$", "", k.strip())] = v.strip()
+    return groups
+
+
+def number(v, default=-1):
+    try:
+        return int(v)
+    except (TypeError, ValueError):
+        return default
+
+
+def panels(groups):
+    """The panels, by containment id: location, lastScreen, and the ids of their system
+    trays' own containments (which sit on the same edge and screen as the panel)."""
+    trays, found = {}, {}
+    for g, keys in groups.items():
+        if len(g) == 5 and g[0] == "Containments" and g[2] == "Applets" and g[4] == "Configuration":
+            tray = keys.get("SystrayContainmentId")
+            if tray:
+                trays.setdefault(g[1], []).append(tray)
+    owned = {t for ts in trays.values() for t in ts}
+    for g, keys in groups.items():
+        if len(g) != 2 or g[0] != "Containments" or number(g[1]) <= 0 or g[1] in owned:
+            continue
+        loc = number(keys.get("location"), 0)
+        if loc in EDGES and keys.get("plugin") != SYSTRAY:
+            found[g[1]] = {"location": loc, "screen": number(keys.get("lastScreen")),
+                           "plugin": keys.get("plugin", "?"), "trays": trays.get(g[1], [])}
+    return dict(sorted(found.items(), key=lambda kv: number(kv[0])))
+
+
+def plan(groups, screens):
+    """(moves, kept): moves are (panel id, from screen, containment ids to put on screen 0);
+    kept are (panel id, from screen, why) for lost panels left alone."""
+    found = panels(groups)
+    taken = {(p["screen"], p["location"]) for p in found.values() if 0 <= p["screen"] < screens}
+    moves, kept = [], []
+    for pid, p in found.items():
+        if p["screen"] < screens:
+            continue  # on a screen this desktop has (Plasma puts -1 on the first one itself)
+        if (0, p["location"]) in taken:
+            kept.append((pid, p["screen"], f"the first screen already has a {EDGES[p['location']]} panel"))
+            continue
+        taken.add((0, p["location"]))
+        moves.append((pid, p["screen"], [pid, *p["trays"]]))
+    return moves, kept
+
+
+def default_screens():
+    sys.path.insert(0, os.path.join(os.path.dirname(os.path.realpath(__file__)), "..", "layout"))
+    import ft_layout
+    return ft_layout.screen_count()
+
+
+def main(argv):
+    ap = argparse.ArgumentParser(description=__doc__.split("\n\n")[0])
+    ap.add_argument("--screens", type=int)
+    ap.add_argument("--file")
+    ap.add_argument("--check", action="store_true")
+    a = ap.parse_args(argv)
+    config = os.environ.get("XDG_CONFIG_HOME") or os.path.expanduser("~/.config/frametop")
+    path = a.file or os.path.join(config, "plasma-org.kde.plasma.desktop-appletsrc")
+    screens = a.screens if a.screens else default_screens()
+    try:
+        with open(path) as f:
+            groups = parse(f.read())
+    except FileNotFoundError:
+        if a.check:
+            print("no Plasma config yet (Plasma makes the default taskbar)")
+        return 0
+    moves, kept = plan(groups, screens)
+
+    if a.check:
+        found = panels(groups)
+        for pid, p in found.items():
+            lost = " (lost: no such screen)" if p["screen"] >= screens else ""
+            print(f"panel {pid}: screen {p['screen']}, {EDGES[p['location']]}{lost}")
+        if not found:
+            print("no panels")
+        print(f"{screens} screen(s)")
+        return 1 if moves or kept else 0
+
+    if moves:
+        shutil.copy2(path, path + ".ft-bak")
+    for pid, was, ids in moves:
+        for cid in ids:
+            subprocess.run(["kwriteconfig6", "--file", os.path.abspath(path), "--group", "Containments",
+                            "--group", cid, "--key", "lastScreen", "0"], check=True)
+        print(f"frametop: panel {pid} was saved on screen {was}, which this desktop doesn't have "
+              f"({screens} screen(s)); moved it to the first screen (backup: {path}.ft-bak)", file=sys.stderr)
+    for pid, was, why in kept:
+        print(f"frametop: panel {pid} is saved on screen {was}, which this desktop doesn't have; "
+              f"left there: {why}", file=sys.stderr)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))

session/frametop-session.sh

@@ -272,4 +272,9 @@ fi
 # with both, apps would open twice.
 kwriteconfig6 --file "$XDG_CONFIG_HOME/ksmserverrc" --group General --key loginMode emptySession
 
+# Plasma keeps a panel on a screen number, and never moves one whose screen this desktop
+# doesn't have, like a spare output or a screen a smaller layout dropped. Put such a panel
+# back on the first (primary) screen before Plasma reads the file (session/fix-panels.py).
+python3 "$here/fix-panels.py" --screens "$screens" || true
+
 dbus-run-session startplasma-wayland

session/tests/test_fix_panels.py

@@ -0,0 +1,162 @@
+#!/usr/bin/env python3
+"""Tests for session/fix-panels.py: issue #18's config (the taskbar saved on spare output 8
+of a 3-screen desktop), panels that are fine, an edge that's taken, and a real run of
+kwriteconfig6 on a copy. Nothing here touches the running desktop or its config.
+
+  python3 session/tests/test_fix_panels.py
+"""
+import importlib.util
+import os
+import subprocess
+import sys
+import tempfile
+import unittest
+
+HERE = os.path.dirname(os.path.realpath(__file__))
+SCRIPT = os.path.join(HERE, "..", "fix-panels.py")
+spec = importlib.util.spec_from_file_location("fix_panels", SCRIPT)
+fp = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(fp)
+
+
+def desktop(cid, screen):
+    return f"""[Containments][{cid}]
+activityId=7e1d1a3c-0000-4000-8000-000000000000
+formfactor=0
+immutability=1
+lastScreen={screen}
+location=0
+plugin=org.kde.plasma.folder
+wallpaperplugin=org.kde.image
+"""
+
+
+def panel(cid, screen, location=4, tray=None):
+    text = f"""[Containments][{cid}]
+activityId=
+formfactor=2
+immutability=1
+lastScreen={screen}
+location={location}
+plugin=org.kde.panel
+wallpaperplugin=org.kde.image
+
+[Containments][{cid}][Applets][{cid}1]
+immutability=1
+plugin=org.kde.plasma.kickoff
+"""
+    if tray:
+        text += f"""
+[Containments][{cid}][Applets][{cid}2]
+immutability=1
+plugin=org.kde.plasma.systemtray
+
+[Containments][{cid}][Applets][{cid}2][Configuration]
+PreloadWeight=90
+SystrayContainmentId={tray}
+
+[Containments][{tray}]
+activityId=
+formfactor=2
+immutability=1
+lastScreen={screen}
+location={location}
+plugin=org.kde.plasma.private.systemtray
+popupHeight=432
+"""
+    return text
+
+
+ISSUE_18 = "\n".join([desktop(1, 0), desktop(18, 1), desktop(19, 2)] + [desktop(20 + i, 3 + i) for i in range(8)]
+                     + [panel(10, 8, tray=11), "[ScreenMapping]\nitemsOnDisabledScreens=\n"])
+
+
+class Plan(unittest.TestCase):
+    def test_issue_18(self):
+        moves, kept = fp.plan(fp.parse(ISSUE_18), 3)
+        self.assertEqual(moves, [("10", 8, ["10", "11"])])
+        self.assertEqual(kept, [])
+
+    def test_panel_on_a_screen_stays(self):
+        for screen in (0, 2, -1):
+            moves, kept = fp.plan(fp.parse(desktop(1, 0) + panel(2, screen, tray=8)), 3)
+            self.assertEqual((moves, kept), ([], []), screen)
+
+    def test_tray_is_not_a_panel(self):
+        found = fp.panels(fp.parse(panel(2, 0, tray=8)))
+        self.assertEqual(list(found), ["2"])
+        self.assertEqual(found["2"]["trays"], ["8"])
+
+    def test_desktops_never_move(self):
+        moves, _ = fp.plan(fp.parse(ISSUE_18), 1)
+        self.assertEqual([m[0] for m in moves], ["10"])
+
+    def test_edge_taken_on_first_screen(self):
+        text = panel(2, 0, tray=8) + panel(10, 8, tray=11)
+        moves, kept = fp.plan(fp.parse(text), 3)
+        self.assertEqual(moves, [])
+        self.assertEqual([k[:2] for k in kept], [("10", 8)])
+
+    def test_other_edge_is_free(self):
+        moves, kept = fp.plan(fp.parse(panel(2, 0) + panel(10, 4, location=3)), 3)
+        self.assertEqual(moves, [("10", 4, ["10"])])
+        self.assertEqual(kept, [])
+
+    def test_two_lost_on_one_edge(self):
+        moves, kept = fp.plan(fp.parse(panel(10, 5) + panel(12, 8)), 3)
+        self.assertEqual([m[0] for m in moves], ["10"])
+        self.assertEqual([k[0] for k in kept], ["12"])
+
+    def test_screen_count_went_down(self):
+        moves, _ = fp.plan(fp.parse(panel(2, 1, location=3)), 1)
+        self.assertEqual(moves, [("2", 1, ["2"])])
+
+
+class Run(unittest.TestCase):
+    def setUp(self):
+        self.dir = tempfile.TemporaryDirectory()
+        self.path = os.path.join(self.dir.name, "plasma-org.kde.plasma.desktop-appletsrc")
+        with open(self.path, "w") as f:
+            f.write(ISSUE_18)
+
+    def tearDown(self):
+        self.dir.cleanup()
+
+    def run_script(self, *args):
+        return subprocess.run([sys.executable, SCRIPT, "--file", self.path, "--screens", "3", *args],
+                              capture_output=True, text=True)
+
+    def test_check_reports_and_changes_nothing(self):
+        r = self.run_script("--check")
+        self.assertEqual(r.returncode, 1)
+        self.assertIn("panel 10: screen 8, bottom (lost", r.stdout)
+        with open(self.path) as f:
+            self.assertEqual(f.read(), ISSUE_18)
+
+    def test_repair(self):
+        r = self.run_script()
+        self.assertEqual(r.returncode, 0, r.stderr)
+        self.assertIn("moved it to the first screen", r.stderr)
+        with open(self.path) as f:
+            groups = fp.parse(f.read())
+        self.assertEqual(groups[("Containments", "10")]["lastScreen"], "0")
+        self.assertEqual(groups[("Containments", "11")]["lastScreen"], "0")
+        self.assertEqual(groups[("Containments", "10", "Applets", "101")]["plugin"], "org.kde.plasma.kickoff")
+        self.assertEqual(groups[("Containments", "25")]["lastScreen"], "8")  # a spare's desktop
+        with open(self.path + ".ft-bak") as f:
+            self.assertEqual(f.read(), ISSUE_18)
+        # A second run finds nothing to do and leaves the backup alone.
+        os.remove(self.path + ".ft-bak")
+        r = self.run_script()
+        self.assertEqual((r.returncode, r.stderr), (0, ""))
+        self.assertFalse(os.path.exists(self.path + ".ft-bak"))
+        self.assertEqual(self.run_script("--check").returncode, 0)
+
+    def test_no_config_yet(self):
+        os.remove(self.path)
+        self.assertEqual(self.run_script().returncode, 0)
+        self.assertEqual(self.run_script("--check").returncode, 0)
+
+
+if __name__ == "__main__":
+    unittest.main()