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, 20 insertions, 0 deletions

diff --git a/src/threadlistmodel.h b/src/threadlistmodel.h
index bed099d..fc7f65a 100644
--- a/src/threadlistmodel.h
+++ b/src/threadlistmodel.h
@@ -20,6 +20,7 @@
 
 #include <QAbstractItemModel>
 #include <QColor>
+#include <QHash>
 #include <QVector>
 
 #include "tagcolors.h"
@@ -450,7 +451,26 @@ private:
     /// than claiming the union as one message's.
     static ThreadNode nodeFor(const ThreadSummary &summary);
 
+    /// The top-level row holding a thread or a message, or -1.
+    ///
+    /// Answered from a hash rather than a walk, because a bulk action asks
+    /// once per message and a walk per message made archiving ten thousand
+    /// rows quadratic in the lookups alone (item 211). The FIRST row in list
+    /// order wins, which is the row every linear walk here used to stop at,
+    /// so the two are interchangeable; a flat view can hold one thread on
+    /// several rows and still answers with the first.
+    int rowForThread(const QString &threadId) const;
+    int rowForMessage(const QString &messageId) const;
+    void rebuildIndex() const;
+
     QVector<ThreadNode> m_threads;
+    // Rebuilt lazily on the next lookup after anything renumbers rows or
+    // changes which ids a node carries. Every structural change signals, and
+    // the two in-place id changes (reconcile, setThreadMessages) mark it by
+    // hand.
+    mutable QHash<QString, int> m_rowByThread;
+    mutable QHash<QString, int> m_rowByMessage;
+    mutable bool m_indexStale = true;
     const TagColors *m_tagColors = nullptr;
     QString m_dateFormat;
     QStringList m_forwardPrefixes;