feat: add ThreadListModel with batch append

QAbstractTableModel over query results, appended in batches so a large
query paints its first screenful immediately. Tag changes apply locally
for optimistic UI; reverting a failed write means calling applyTagChange
again with added and removed swapped, which the round-trip test pins.

Two additions to the drafted version:

- A ThreadIdRole, so a view's QModelIndex maps back to the thread id the
  worker speaks without every caller reaching around the model.
- data() checks its own row and column bounds. Qt will not hand out an
  out-of-range index and invalidates persistent ones on reset, so this is
  unreachable defence rather than a live path; the test says so instead of
  pretending to cover it.

Verified by mutation that the empty-batch guard, the ThreadIdRole, and the
full-row dataChanged range each fail exactly one test when removed.

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

1 files changed, 50 insertions, 0 deletions

diff --git a/src/threadlistmodel.h b/src/threadlistmodel.h
new file mode 100644
index 0000000..2cf8d2e
--- /dev/null
+++ b/src/threadlistmodel.h
@@ -0,0 +1,50 @@
+#pragma once
+
+#include <QAbstractTableModel>
+#include <QVector>
+
+#include "types.h"
+
+/// Table model over query results, filled in batches so a large query paints
+/// its first screenful immediately.
+class ThreadListModel : public QAbstractTableModel
+{
+    Q_OBJECT
+public:
+    enum Column {
+        DateColumn = 0,
+        AuthorsColumn,
+        SubjectColumn,
+        TagsColumn,
+        ColumnCount,
+    };
+
+    enum Role {
+        /// The thread id behind a row. Views hand out QModelIndexes, but the
+        /// worker speaks thread ids, so the mapping belongs on the model
+        /// rather than in every caller.
+        ThreadIdRole = Qt::UserRole + 1,
+    };
+
+    explicit ThreadListModel(QObject *parent = nullptr);
+
+    int rowCount(const QModelIndex &parent = {}) const override;
+    int columnCount(const QModelIndex &parent = {}) const override;
+    QVariant data(const QModelIndex &index, int role) const override;
+    QVariant headerData(int section, Qt::Orientation orientation,
+                        int role) const override;
+
+    void appendBatch(const QVector<ThreadSummary> &batch);
+    void clear();
+
+    ThreadSummary threadAt(int row) const;
+
+    /// Applies a tag change locally so the UI updates before the worker
+    /// confirms. To revert a failed write, call again with added and removed
+    /// swapped.
+    void applyTagChange(const QString &threadId, const QStringList &added,
+                        const QStringList &removed);
+
+private:
+    QVector<ThreadSummary> m_threads;
+};