feat: snapshot the pending changes as rows

Item 119, first half: the data the list behind the unsynced-changes count
is built from, with no dialog and no worker, so the rules it has to follow
are testable on their own.

pendingChangeSnapshot() gathers the three queues the count sums into
PendingChange rows. Two properties are the whole point.

Scope follows the ACTION, not the storage. A held thread edit stays one
thread row, because a `*_thread` action made it and reporting its messages
instead would claim the user acted on each one; a netted tag edit and a held
move are message rows. The queues already encode that distinction, so
nothing is expanded and nothing is escalated.

The rows are grouped by id, so a message with several outstanding actions
appears once with its actions beneath it, which is the layout the user
asked for. The sort is stable, so those actions keep the order they were
made in; QHash has none of its own, and without it the list would reshuffle
between openings.

A snapshot, taken once and frozen. Subjects are empty here and filled by the
resolve step to come.

m_pendingTagEdits gains the action name beside the direction it already
kept. The direction alone was enough to count with; a list has to say what
each change was, and only the action that made it knows. It is carried from
TagChange::description rather than derived from the tag, so there is no
second table of tag names to labels to drift from the first.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P88Q3MCSCSQxKDy7pmXh9F

1 files changed, 38 insertions, 4 deletions

diff --git a/src/mainwindow.h b/src/mainwindow.h
index 25a9a7f..532a5ea 100644
--- a/src/mainwindow.h
+++ b/src/mainwindow.h
@@ -105,6 +105,24 @@ public:
     /// the worker, which test_mainwindow has no database to drive.
     bool hasEditAwaitingSend() const { return !m_heldEdits.isEmpty(); }
 
+    /// Every outstanding change, as rows, for the list behind the count.
+    ///
+    /// A SNAPSHOT: taken once when the user opens the list and never refreshed
+    /// under them. Subjects are empty here, filled by the resolve step, so
+    /// this is testable with no worker and no database.
+    ///
+    /// Scope follows the ACTION. The three queues already encode it: a held
+    /// thread edit carries thread ids because a `*_thread` action made it,
+    /// while a netted tag edit and a held move both carry message ids. Nothing
+    /// is expanded, and nothing is escalated.
+    /// Net changes the index holds that a sync has not carried over.
+    ///
+    /// Public beside pendingChangeSnapshot(), which must agree with it: the
+    /// count the user clicks is the count the list has to account for.
+    int pendingEditCount() const;
+
+    QVector<PendingChange> pendingChangeSnapshot() const;
+
     /// Whether the undo stack still holds anything. Exposed so a test can show
     /// that a rejected write did not take unrelated history down with it.
     bool canUndo() const { return m_undoStack.canUndo(); }
@@ -853,11 +871,14 @@ private:
 
     /// Records one confirmed (message, tag) change, cancelling it against an
     /// opposite change already outstanding for the same pair.
+    ///
+    /// `action` is the name the user would recognise, carried through so the
+    /// list behind the count can say what each change was. It is the
+    /// TagChange's own description rather than anything derived from the tag.
     void recordPendingEdit(const QString &messageId, const QString &tag,
-                           bool added);
+                           bool added, const QString &action);
+
 
-    /// Net changes the index holds that a sync has not carried over.
-    int pendingEditCount() const;
 
     /// Shows or hides the "syncing" state: the progress bar and a disabled
     /// Sync button.
@@ -1539,7 +1560,20 @@ private:
     /// value true for added and false for removed; a pair that reverts is
     /// erased rather than stored, so an edit and its inverse leave nothing
     /// behind and the map cannot grow without bound.
-    QHash<QString, bool> m_pendingTagEdits;
+    /// What one pending (message, tag) edit is: its direction, and the name of
+    /// the action that made it.
+    ///
+    /// The direction alone was enough while this only had to be counted. The
+    /// list behind the count (item 119) has to SAY what each change was, and
+    /// only the action that made it knows: `+deleted` is a Delete and
+    /// `-unread` is a Mark read, but deriving that here would be a second
+    /// table of tag names to labels, drifting from the one the actions already
+    /// pass as TagChange::description.
+    struct PendingEdit {
+        bool added = false;
+        QString action;  ///< Translated, from TagChange::description.
+    };
+    QHash<QString, PendingEdit> m_pendingTagEdits;
 
     /// Marks the open thread read once it has been on screen long enough.
     ///