ssh-client keeps ~/.ssh to what it knows: sweep every other path into a kept folder (issue 1017, ADR 0415)

ssh-client owns ~/.ssh, but treated every file it did not place as found, so a
predecessor's drop-in and old copies stayed there for weeks. Its process now
sweeps at start and every ten minutes: keys at any depth (and links to them),
authorized_keys, authorized_keys2 and sockets stay, and a folder holding one is
gone into; everything else moves to ~/.local/state/ssh-client/retired/<UTC
time>/, a folder never shared with another sweep, with a list beside it, which
ssh_client_check shows. Nothing is deleted.

modules/ssh-client/cmd/ssh-client-tools/main.go

@@ -52,7 +52,8 @@ func tools(c *Client) []stdio.Tool {
 		{
 			Name: "ssh_client_check",
 			Description: "Everything about ~/.ssh worth a look: modes of the directory and every file, private keys with no passphrase or weak or old, the mesh's region first with its include, " +
-				"duplicate hosts, known_hosts entries for the mesh's machines that are missing or stale (scanned live unless scan is false), authorized keys without a comment, and debris. Says what it did not check.",
+				"duplicate hosts, known_hosts entries for the mesh's machines that are missing or stale (scanned live unless scan is false), authorized keys without a comment, " +
+				"and what the sweep moved out of ~/.ssh because this module does not know it, with where each lies now (ADR 0415). Says what it did not check.",
 			Input: map[string]any{"scan": map[string]any{"type": "boolean", "description": "ask each of the mesh's machines for its host key now (default true; 5 s each, in parallel)"}},
 			Run:   func(args map[string]any) (any, error) { return c.Check(ctx, flag(args, "scan", true)) },
 		},
@@ -149,10 +150,20 @@ func startKeeper() {
 	if node == "" || err != nil || c.Home == "" {
 		return
 	}
+	go keepSwept(c)
 	k := &KeyKeeper{Home: c.Home, Node: node, Account: u.Username, Run: ExecRunner, State: keysState{}, Now: time.Now}
 	k.Keep(context.Background(), func(f string, a ...any) { fmt.Fprintf(os.Stderr, "[ssh-client] "+f+"\n", a...) })
 }
 
+// keepSwept sweeps ~/.ssh (sweep.go) now and every KeyRound.
+func keepSwept(c *Client) {
+	say := func(f string, a ...any) { fmt.Fprintf(os.Stderr, "[ssh-client] "+f+"\n", a...) }
+	for {
+		c.SweepOnce(time.Now(), say)
+		time.Sleep(KeyRound)
+	}
+}
+
 type keysState struct{}
 
 func (keysState) Put(key string, value any) error {