feat(ui): act on the message a row displays, not its whole thread

A thread's card has rendered one message since item 66, but every tag
action still acted on the entire conversation. Delete, Archive,
Important, Mark spam and Toggle unread now act on the message the card
shows; the whole-thread versions move to a "Whole thread" submenu in the
Message menu and the thread list's context menu, on Ctrl+Alt+<key>.

Closes items 87, 88, 105, 106, 107, 108, 109, 110 and 111.

The defects fixed along the way, several found by reading rather than by
report:

- threadAt(current.row()) answered about the wrong thread for a reply
  row, because a tree numbers rows per parent. The audit found four live
  sites, not the one reported: Delete and Toggle unread each chose their
  DIRECTION from an unrelated thread, and the tag dialog counted the
  wrong thread's tags. threadFor(index) replaces them.

- A message-scoped write made no optimistic model update and no reply
  row carried a doomed cue, so acting on a reply moved the pending-edit
  count and changed nothing on screen.

- Both toggles read the state of a reply's THREAD, which a
  message-scoped write never changes, so they were one-way: the second
  press re-sent a tag the message already had.

- flushHeldEdits() re-sent only thread-scoped edits, so a tag change
  made on one message during a sync was applied to the row, counted as
  unsynced, and then dropped without ever being written.

- applyTagChange() updated a thread's summary but not its loaded
  replies, leaving an expanded thread's rows describing a state the
  database no longer held.

- A thread's first message is not among its children, so both
  message-scoped lookups missed it: acting on a root card repainted
  nothing and emptied the message pane's chip row.

- ThreadSummary::tags is notmuch's union over the thread, so a card
  standing for one message drew tags belonging to its siblings. The
  worker now reads that message's own tags in the walk that already
  finds its id, so the split is known before a row is ever opened.

The card shows both tiers: its own message's tags at full size, the rest
of the conversation's smaller and muted, so nothing appears to vanish
when a row is selected.

Auto mark-read is message-scoped as a result, and now arms for a reply,
which it never did. With maildir.synchronize_flags on, the old
thread-wide write reached the server for mail that had never been
displayed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/types.h b/src/types.h
index f4eaeba..409ce79 100644
--- a/src/types.h
+++ b/src/types.h
@@ -48,6 +48,20 @@ struct ThreadSummary
     /// with recipients; the two have nothing in common but their position here.
     QString firstMessageId;
 
+    /// The tags of that ONE message, as opposed to `tags` above, which is
+    /// notmuch's union over the whole thread.
+    ///
+    /// A card stands for one message but sits above a conversation, and shows
+    /// both: its own tags at full size, the thread's others smaller (item
+    /// 111). Without this the split is unknown until the row is opened and the
+    /// message loads, so every chip renders as the card's own and then shrinks
+    /// on selection, which is what the user reported.
+    ///
+    /// Free, for the same reason `firstMessageId` is: the walk that finds that
+    /// message is already happening and this reads the INDEX, not the message
+    /// file. Do not move it behind a flag by analogy with `recipients`.
+    QStringList firstMessageTags;
+
     /// Who the thread's messages were sent TO, summarised for one line.
     ///
     /// Empty unless the query asked for it, and that is a performance
@@ -140,6 +154,15 @@ struct MessageNode
     {
         return tags.contains(QStringLiteral("attachment"));
     }
+
+    bool isDeleted() const { return tags.contains(QStringLiteral("deleted")); }
+    bool isSpam() const { return tags.contains(QStringLiteral("spam")); }
+
+    /// True while the message is tagged for removal, exactly as the thread
+    /// predicate of the same name. A reply carries its own fate: a
+    /// message-scoped Delete tags one message, and the reply's row is the only
+    /// place the user can see that happen.
+    bool isDoomed() const { return isDeleted() || isSpam(); }
 };
 
 /// What an action is about to touch, resolved from the selection.