over: ensure old, merged {tid} is really gone

We must use the result of link_refs() since it can trigger
merge_threads() and invalidate $old_tid.  In case
merge_threads() isn't triggered, link_refs() will return
$old_tid anyways.

When rethreading and allocating new {tid}, we also must update
the row where the now-expired {tid} came from to ensure only the
new {tid} is seen when reindexing subsequent messages in
history.  Otherwise, every subsequently reindexed+rethreaded
message could end up getting a new {tid}.

Reported-by: Kyle Meyer <kyle@kyleam.com>
Link: https://public-inbox.org/meta/87360nlc44.fsf@kyleam.com/
(cherry picked from commit 9356ec0cc5afc95a8fd398ddf898942ef0acdb74)

1 files changed, 1 insertions, 0 deletions

diff --git a/MANIFEST b/MANIFEST
index f3620de4..6c1cdecc 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -354,6 +354,7 @@ t/solver_git.t
 t/spamcheck_spamc.t
 t/spawn.t
 t/thread-cycle.t
+t/thread-index-gap.t
 t/time.t
 t/uri_imap.t
 t/utf8.eml