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, 29 insertions, 0 deletions

diff --git a/src/keymap.cpp b/src/keymap.cpp
index f6ef6a4..c731bbb 100644
--- a/src/keymap.cpp
+++ b/src/keymap.cpp
@@ -37,6 +37,21 @@ QStringList KeyMap::knownActions()
         QStringLiteral("edit_tags"),
         QStringLiteral("tag_rules"),
         QStringLiteral("flag"),
+        // The whole-thread counterparts (item 108). The names above act on the
+        // message a row displays; these act on its entire thread. Separate
+        // names rather than a scope flag, because a name is what a user writes
+        // in [keys]: giving `delete` new semantics would silently change an
+        // existing config, and renaming it would break one that mentions it.
+        //
+        // Unbound by default. They are reached through the "Whole thread"
+        // submenu, and inventing five more default chords for actions most
+        // users will rarely want is worse than leaving them to bind what they
+        // use.
+        QStringLiteral("archive_thread"),
+        QStringLiteral("delete_thread"),
+        QStringLiteral("spam_thread"),
+        QStringLiteral("toggle_unread_thread"),
+        QStringLiteral("flag_thread"),
         QStringLiteral("focus_query"),
         QStringLiteral("complete_query"),
         QStringLiteral("save_query"),
@@ -90,6 +105,20 @@ QList<QPair<QString, QString>> KeyMap::defaultBindings()
         // action takes the harder chord rather than the easier one.
         { QStringLiteral("Ctrl+Shift+U"), QStringLiteral("mark_all_read") },
         { QStringLiteral("Ctrl+I"),       QStringLiteral("flag") },
+        // The whole-thread tier (item 108), one modifier out from each
+        // message-scoped twin: Ctrl+D deletes the message a row displays,
+        // Ctrl+Alt+D deletes its conversation.
+        //
+        // Ctrl+ALT, not Ctrl+Shift. The obvious pairing is taken twice over:
+        // Ctrl+Shift+S is `spam` and Ctrl+Shift+U is `mark_all_read`, both
+        // shipped and both in users' fingers. Reusing either would silently
+        // change what an existing key does, which is the same objection that
+        // made these separate action names rather than a flag on the old ones.
+        { QStringLiteral("Ctrl+Alt+E"),   QStringLiteral("archive_thread") },
+        { QStringLiteral("Ctrl+Alt+D"),   QStringLiteral("delete_thread") },
+        { QStringLiteral("Ctrl+Alt+S"),   QStringLiteral("spam_thread") },
+        { QStringLiteral("Ctrl+Alt+U"),   QStringLiteral("toggle_unread_thread") },
+        { QStringLiteral("Ctrl+Alt+I"),   QStringLiteral("flag_thread") },
         { QStringLiteral("Ctrl+T"),       QStringLiteral("edit_tags") },
         // Shifted against Ctrl+T for the same reason Ctrl+Shift+U is shifted
         // against Ctrl+U: this is the standing version of tagging, applied to