fix(media): order the sidecar reap only where the view is mounted

Every apply and rollback printed "next: scripts/media-view.sh reap", but on
Dankserver there is nothing to reap: the metadata view has never been installed
(`media-view.sh status` -> NOT MOUNTED, `/var/lib/media-meta` absent) and the
live quadlets still bind the array read-only. All three relayout arms tonight
issued that order — 242,084 moves — and it pointed at a directory that does not
exist. Where no overlay is mounted the servers bind the array itself, so the
sidecars moved with the media.

`--metadata-view` (default /var/lib/media-meta/view) names the overlay and the
note now rides only when that path is a mountpoint. Red first: two new cases in
tests/media_relayout.bats (apply and rollback); the shared helper names a real
mountpoint so the pre-existing presence assertion keeps its meaning. 37 ok.

tests/media_relayout.bats

@@ -374,7 +374,10 @@ PY
 # apply_plan — plan, then apply for real; the journal goes in the tmpdir.
 apply_plan() {
     JOURNAL="$BATS_TEST_TMPDIR/journal.jsonl"
-    run python3 "$APPLY" apply --plan "$OUT" --root "$LIB" --journal "$JOURNAL" --apply
+    # `/` is always a mountpoint, so the overlay note behaves as it does on a
+    # host that runs the metadata view.
+    run python3 "$APPLY" apply --plan "$OUT" --root "$LIB" \
+        --journal "$JOURNAL" --metadata-view / --apply
 }
 
 @test "a run without --apply says what it would do and touches nothing" {
@@ -409,6 +412,32 @@ print(sum(1 for l in open(sys.argv[1]) if json.loads(l).get("op") == "move"))' "
     [ "$status" -eq 0 ]
 }
 
+# The overlay note is only true where the metadata view is really mounted. On a
+# host whose media servers bind the array directly (dankserver today: both
+# quadlets mount /mnt/entropy, /var/lib/media-meta does not exist) the sidecars
+# moved with the media, and "next: run reap" is an order that cannot be carried
+# out. --metadata-view is how the caller names that path; the default is the
+# host's view path, and the note rides only when it is a mountpoint.
+@test "an apply with no mounted metadata view does not order a reap" {
+    plan
+    JOURNAL="$BATS_TEST_TMPDIR/journal.jsonl"
+    run python3 "$APPLY" apply --plan "$OUT" --root "$LIB" --journal "$JOURNAL" --apply
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"moved"* ]]
+    [[ "$output" != *"media-view.sh reap"* ]]
+}
+
+@test "a rollback with no mounted metadata view does not order a reap" {
+    plan
+    JOURNAL="$BATS_TEST_TMPDIR/journal.jsonl"
+    run python3 "$APPLY" apply --plan "$OUT" --root "$LIB" --journal "$JOURNAL" --apply
+    [ "$status" -eq 0 ]
+    run python3 "$APPLY" rollback --journal "$JOURNAL" --root "$LIB" --apply
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"rolled back"* ]]
+    [[ "$output" != *"media-view.sh reap"* ]]
+}
+
 @test "a target already holding a different file stops the whole run" {
     plan
     JOURNAL="$BATS_TEST_TMPDIR/journal.jsonl"