The existing multi-disk EC integration test asserts on shard counts. Counting
cannot tell a healthy volume from one a repair reassembled out of the wrong
inputs — both have fourteen shards. This drives the real shell commands
(ec.encode, ec.balance, ec.rebuild) against a live three-node, four-disk
cluster and reads the stored bytes back after every step, so a rebuild that
produced fourteen plausible-but-wrong shards fails here.
An 8 KB random payload is stored, then encoded, balanced, damaged (two shard
files removed and the servers restarted so the master relearns the reduced
set from disk), and rebuilt. The rebuild output matches the shape of the
support case that motivated this — "rebuildOneEcVolume", "missing shard N.0",
"copied N.1 from ..." — and the payload is verified identical after each of
upload, encode, balance, shard loss, and rebuild.
Two ordering facts the test pins, both of which cost real debugging time:
ec.rebuild is driven by the master's topology, not disk truth, so shards must
be relearned (via restart) before a repair can target the right set; and the
shell lock is dropped when the restart disconnects the master, so it has to be
retaken before the rebuild.
