fix(listing): snapshot asynchronous cache cleanup inputs

Capture the metacache peer before launching cleanup and pass listing
options by value. The parent can clear its cache ID without changing the
background RPC lookup or racing with its reads of shared request state.

Publish complete immutable disk snapshots through atomic.Value in the
listing fixtures instead of replacing getDisks after requests start.
Add a real peer RPC regression for cleanup using the original cache ID;
reverting the options copy reproduces both the race and an empty RPC ID.

Verified the final 18-test listing race suite, 30 repetitions of the real
peer regression, formatting checks and make lint. Prior runtime evidence
retains its original e90cb206 source identity.

Refs: https://github.com/pgsty/silo/issues/218
Refs: https://github.com/pgsty/silo/pull/239
Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/metacache-server-pool.go

@@ -191,19 +191,19 @@ func (z *erasureServerPools) listPath(ctx context.Context, o *listPathOptions) (
 			return entries, err
 		}
 		entries.truncate(0)
-		go func() {
-			rpc := globalNotificationSys.restClientFromHash(pathJoin(o.Bucket, o.Prefix))
+		rpc := globalNotificationSys.restClientFromHash(pathJoin(o.Bucket, o.Prefix))
+		go func(o listPathOptions) {
 			if rpc != nil {
 				ctx, cancel := context.WithTimeout(GlobalContext, 5*time.Second)
 				defer cancel()
-				c, err := rpc.GetMetacacheListing(ctx, *o)
+				c, err := rpc.GetMetacacheListing(ctx, o)
 				if err == nil {
 					c.error = "no longer used"
 					c.status = scanStateError
 					rpc.UpdateMetacacheListing(ctx, *c)
 				}
 			}
-		}()
+		}(*o)
 		o.ID = ""
 	}