feat(worker): load a thread as a reply tree with per-message depth

loadThread could not be extended to do this. It walks
notmuch_query_search_messages, and a message obtained that way returns NULL from
notmuch_message_get_replies (notmuch.h:1617-1628), so that walk cannot produce
reply depth at all. The tree comes from notmuch_thread_get_toplevel_messages
instead, and the pane keeps the flat list it wants.

walkReplies takes raw notmuch_message_t*, against this file's rule that every
handle is RAII-owned. Messages reached through a thread are freed with it
(notmuch.h:1637), so an NmMessage wrapper would destroy memory the thread frees
again. The NmThread in the caller is what keeps them alive.

Every message in the thread gets a node regardless of the query: the list is
where the reply count is read, and hiding unmatched replies would make that
count disagree with the rows under it.

Both tests mutation-checked. Flattening depth fails the depth assertion, and
skipping the thread walk fails it too, so neither passes against the two
mistakes the notmuch API invites.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/types.h b/src/types.h
index 6b2ca4c..ef822b9 100644
--- a/src/types.h
+++ b/src/types.h
@@ -124,5 +124,6 @@ struct DatabaseStats
 
 Q_DECLARE_METATYPE(ThreadSummary)
 Q_DECLARE_METATYPE(MessageRef)
+Q_DECLARE_METATYPE(MessageNode)
 Q_DECLARE_METATYPE(TagChange)
 Q_DECLARE_METATYPE(DatabaseStats)