import: rewrite less history during purge

We do not need to rewrite old commits unaffected by the object_id
purge, only newer commits.  This was a state management bug :x

We will also return the new commit ID of rewritten history to
aid in incremental indexing of mirrors for the next change.

1 files changed, 2 insertions, 1 deletions

diff --git a/t/v2writable.t b/t/v2writable.t
index 2f839776..e49c06b9 100644
--- a/t/v2writable.t
+++ b/t/v2writable.t
@@ -248,7 +248,8 @@ EOF
 {
         ok($im->add($mime), 'add message to be purged');
         local $SIG{__WARN__} = sub {};
-        ok($im->purge($mime), 'purged message');
+        ok(my $cmts = $im->purge($mime), 'purged message');
+        like($cmts->[0], qr/\A[a-f0-9]{40}\z/, 'purge returned current commit');
         $im->done;
 }