fix: keep bulk tag actions linear, and say when they land

Select all on a 10k-row search, then Archive, froze the window with one
CPU pinned. gdb on the live process showed the UI thread cubic before the
write was ever sent: each optimistic row write emitted dataChanged, whose
handler refreshed the action labels by walking the whole selection, and
each step of that walk looked the message up with a linear scan of every
thread.

ThreadListModel now answers id lookups from a lazily rebuilt hash,
invalidated by its own structural signals and by hand at the two in-place
id changes. MainWindow::batchModelWrites() holds the label refresh while a
loop of optimistic writes runs, then refreshes once. Two list membership
tests became sets.

The announcement also used to fade on a timer whether or not the write
had landed. It now reads "applying" until a round trip through the
worker's queue says the write has run, then "done". An error takes the
label back from a late "done".

Item 211.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/mainwindow.h b/src/mainwindow.h
index 87ed171..868964a 100644
--- a/src/mainwindow.h
+++ b/src/mainwindow.h
@@ -1179,6 +1179,10 @@ private:
     /// something, the same rule refreshUnreadAction() applies to the label.
     void refreshTrashActions();
 
+    /// Runs a loop of optimistic model writes with the dataChanged-driven
+    /// action refresh held, then refreshes once (item 211).
+    void batchModelWrites(const std::function<void()> &writes);
+
     /// Whether every selected row's file already sits in its account's trash
     /// folder. Empty selection answers false.
     ///
@@ -1209,6 +1213,8 @@ private:
     /// for exit has finished. Stops closeEvent asking a second time, and is
     /// what lets the deferred close through.
     bool m_closeApproved = false;
+    bool m_batchingModelWrites = false;   ///< see batchModelWrites()
+    quint64 m_announceTicket = 0;   ///< see announceAction()
 
     /// True while a sync started by the exit prompt is running. The window
     /// stays open until it finishes: killing the process mid-sync is exactly