plasma-phone-ui/xfce4/weston blank screen on nexus 5 (lg-hammerhead)

It was working many weeks ago, then broken a few weeks ago, and still broken now. Looks like several things have changed. For one, start-plasma.sh switched away from wl-shell because of a qt bug, and changed some of its initialization steps. For another, kde has been updated at least once.

These are the log bits that look relevant:

X-Server started on display :0
/usr/bin/plasma-phone: line 33: /usr/lib/libexec/ksyncdbusenv: not found

Error org.freedesktop.DBus.Error.ServiceUnknown: The name com.google.code.AccountsSSO.SingleSignOn w
as not provided by any .service files

Error org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.Telepathy.MissionControl5 
was not provided by any .service files

/usr/bin/plasma-phone: /usr/bin/plasma-phone: line 46: /usr/lib/libexec/org_kde_powerdevil: not found

line 43: /usr/lib/libexec/polkit-kde-authentication-agent-1: not found

...

org.kde.knotifications: env says KDE is running but SNI unavailable -- check KDE_FULL_SESSION and XDG_CURRENT_DESKTOP

...

Activating service name='org.kde.ActivityManager'

qt.qpa.xcb: could not connect to display 

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.

This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.