/etc/systemd/system/sleep.target.wants/syncthing-resume.service is a
dangling symlink pointing to /lib/systemd/system/syncthing-resume.service,
which does not exist anywhere on the filesystem and is not shipped by the
currently installed syncthing package (1.30.0) or owned by any installed
package (dpkg -S finds no match for either the symlink or its target).

Evidence this is postinst-created leftover, not user error:

- The symlink's mtime (2026-02-17 16:22:22) matches, to the second, the
  original syncthing 1.19.2~ds1-1+b4 install completing on this system,
  per /var/log/dpkg.log:

    2026-02-17 16:22:29 install syncthing:amd64 <none> 1.19.2~ds1-1+b4
    2026-02-17 16:22:30 configure syncthing:amd64 1.19.2~ds1-1+b4 <none>
    2026-02-17 16:22:31 status installed syncthing:amd64 1.19.2~ds1-1+b4

- The package was later upgraded in place to 1.30.0 on 2026-04-08:

    2026-04-08 11:56:59 upgrade syncthing:amd64 1.19.2~ds1-1+b4 1.30.0
    2026-04-08 12:57:00 status installed syncthing:amd64 1.30.0

  The symlink survived this upgrade completely untouched — its mtime is
  still the original Feb 17 install time, and the current package's
  postinst evidently has no logic to detect or remove enablement symlinks
  left behind by an older version's unit that no longer exists in the
  current package (dpkg -L syncthing currently lists only
  syncthing@.service and the user-mode syncthing.service, no "resume"
  unit at all).

Net effect: a broken symlink sits in sleep.target.wants/ indefinitely,
harmless functionally (systemd just fails to find the target and logs it
without blocking sleep), but it's dead weight that should have been
cleaned up by prerm/postinst when the unit it referenced stopped being
shipped.