Hold what mounts a missing disk, and say entries the mesh could not take out (hq ADR 0325 re-review)

A container was still created over an unmounted mount point, so its writes landed on
the filesystem below; a folder moved to another disk was kept on the old warrant; and
entries left by a drop or a move that could not run lived only in a log line. Every
container mounting an access whose disk is away now waits, the warrant holds only for
the filesystem it was carried out on (the wait names the new one, path-free), entries
left on a filesystem are recorded per mount and taken out when it is back, and every
leftover is said as unhealthy until it is. A hung stat is shared per path, and a
widened mask takes from other entries only the bits it adds.

internal/link/messages.go

@@ -309,6 +309,11 @@ const KindDirectory = "directory"
 // it yet or its disk is not there (§7), unhealthy otherwise — root's data on its placed filesystem among it (§12).
 const KindAccess = "access"
 
+// KindKeptEntries is the mesh's entries on a shared folder that nobody wants and that could not be taken out yet
+// (novox/hq ADR 0325 §8): a folder no access names whose disk is away, or entries left on a filesystem no longer at
+// a folder. Unhealthy, said under the access that last named it, until the drop walk has run.
+const KindKeptEntries = "kept-entries"
+
 // ReasonUsedAsFound starts the reason of a directory used as found.
 const ReasonUsedAsFound = "used as found:"
 
@@ -445,6 +450,9 @@ type AccessWait struct {
 	Access string `json:"access"`
 	Part   string `json:"part"`
 	What   string `json:"what"`
+	// Placed names, with no path, the filesystem the folder is on now, on a wait for the operator's word: a warrant
+	// given for another filesystem (the folder moved) does not answer it, and the controller asks again.
+	Placed string `json:"placed,omitempty"`
 }
 
 // KeptEntry is one user of a kept folder as its listing says it.