mounts: clear a failed mount of its own whose source was away, and the failure of a unit it takes over, so neither is said as the machine's own failed unit (hq ADR 0263 rules 4 and 6)

modules/mounts/README.md

@@ -42,6 +42,14 @@ an autofs mount, so nothing writes into the empty directory under it.
 | an SMB source | `//<host>/<share>`, `Type=cifs` | `credentials=<file>,iocharset=utf8,_netdev,nofail,uid=…,gid=…` | 10 |
 | a disk | `/dev/disk/by-uuid/<uuid>`; the mount `BindsTo=` the disk's device | `nofail` | 10 |
 
+A mount of the module's own that failed because its source was not there — an occasional source that is
+off, or a node's share whose server is away, tried when someone opened the mount point — is cleared
+(`systemctl reset-failed`) by `apply` within five seconds, and so is the failure a unit of the same name
+carried before the module wrote it (the unit fstab's generator makes until the line is adopted). The module
+says such a share as `absent` or `unreachable`; left failed, the unit would also be said as a failed unit of
+the machine's own, with a notification each time it is touched. A mount that failed while its source answers
+is left failed: that is a fault, and the share is said `failed`.
+
 A share is read-only when the setting says `:ro` or the sharing machine exports it read-only. A
 read-write share is mounted hard, so a write is never dropped while the server is away.